Zinc bis(dihydrogen phosphate)

Endpoint summary

Additional information

In this dossier, the endpoint exposure related observations in humans is not addressed by substance-specific information, but instead by a weight of evidence approach based on collected information for all zinc substances of the zinc category. The assessment of the effects in humans of zinc and its substances is related to the assumption that once inorganic zinc compounds or zinc metal become bioavailable, this will be in the form of the divalent zinc cation. Further assuming that the anion of such inorganic zinc compounds can be regarded as “inert” with regard to repeated dose toxicity, the subsequent discussion focuses on the zinc cation. Further information on the read-across approach are given in the report attached to IUCLID section 13.2.

 

Human data - Epidemiological studies, RDT oral exposure

 

Epidemiological studies, RDT oral exposure - Controlled studies with volunteers

The study by Ghaffari et al. 2014 represents a randomized, double-blind, placebo-controlled clinical trial in zinc-deficient children with asthma and the effects of zinc supplementation on the health status of the patients.
345 patients attending the public outpatient allergy clinic at Mazandaran University of Medical Sciences (Iran) between August 2010 and May 2011 were assessed for eligibility, 30 did not meet the inclusion criteria, 10 declined to participate and 5 were excluded for other reasons. The remaining 300 patients were enrolled in the clinical trial and randomized to either the case (n=155) or the control group (n=145). All patients in this study were using fixed inhaled steroids (moderate dose of fluticasone).
The patients’ clinical data were assessed. Clinical symptoms (cough, wheezing, dyspnoea), spirometry indices and serum zinc and IgE levels were recorded before and after the intervention. Pulmonary function testing was performed for forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and FEV1/FVC. A 5 mL sample of blood was taken from all patients for serum zinc analysis. Complete blood count, eosinophil count and serum total IgE level was performed.
Patients judged to have moderate asthma with associated zinc deficiency (<70 μg/dL) were randomized to the intervention (zinc supplements, 50 mg/day) or control (placebo) group. Patients were blind to the treatment for 8 weeks.
Data were analysed for the 144 cases and 140 controls who completed the study. The mean serum zinc level was 61.8 (SD 7.3) μg/dL and 60.9 (SD 4.3) μg/dL in the case and control groups, respectively, before treatment. After treatment, the serum mean levels of zinc increased statistically significantly (P<0.001) to 129 (SD 20.4) μg/dL in the case group compared with 63 (SD 8.6) μg/dL in the controls. There was no significant difference in IgE levels in both groups before and after treatment.
There were significant improvements in the case group compared with the control group in all the clinical symptoms evaluated: cough (p=0.003), wheezing (p<0.001) and dyspnoea (p<0.001). Zinc supplementation had a significant effective on all parameters of spirometry (p<0.01 or 0.001).
In this randomized, double-blind, placebo-controlled clinical trial it was shown that zinc supplementation at 50 mg/day in children with moderate asthma with zinc deficiency significantly improved both clinical symptoms and lung function.
This well designed and adequately reported clinical trial revealed a positive effect of zinc supplementation on the clinical symptoms of children patients with zinc deficiency and supports the evidence of the important role of a balanced zinc supplementation and status for the health of patients.

In this community-based, double-blind, placebo-controlled, cluster randomised trial by Somé et al. 2015, the effects of different amounts and sources of zinc on the frequency of diarrhoea, malaria, fever and respiratory tract infections (RTI) in young children was assessed.
This community-based trial (iLiNS-Zinc study) was conducted in 2 435 children of 9 months of age between April 2010 and July 2012 in rural southwestern Burkina Faso. Children were eligible if they were 8.80–9.99 months old, a permanent resident of Dandé health district, and their caregivers planned to be available during the study period and accepted home visits for data collection. Children were excluded when they had haemoglobin (Hb) concentration <50 g/L, weight-for-length <70% of the National Center of Health Statistics (NCHS) reference median, bipedal oedema, other severe illness requiring hospital referral, a congenital abnormality or chronic medical condition, allergy towards peanuts or history of anaphylaxis or serious allergic reactions. During the enrolment visit, length and weight were measured and all children were screened for malaria parasites.

Participants were randomly assigned at the concession level to receive daily 1 of 4 interventions for 9 months: (1) 20 g small-quantity lipid-based nutrient supplement (SQ-LNS) without zinc and placebo tablet, (2) 20 g SQ-LNS with 5 mg zinc and placebo tablet, (3) 20 g SQ-LNS with 10 mg zinc and placebo tablet or (4) 20 g SQ-LNS without zinc and 5 mg zinc tablet. Participants were visited weekly in their homes for morbidity surveillance for 9 months. Field data collectors used a structured questionnaire to collect a weekly morbidity history, including the child’s general state, appetite, number of semiliquid/liquid stools, presence of blood or mucus in stools, vomiting, fever, signs of respiratory tract infections, and any treatment received by the child either from study staff members or outside the study. As a quality control measure, auricular temperature was also measured once per month for all children. Children with uncomplicated diarrhoea and malaria received treatment from the study field workers in the community. Children were referred to the nearest health clinic for any danger signs (convulsions, lethargy or coma, persistent vomiting or inability to eat or drink), diarrhoea and malaria with complications, suspicion of lower respiratory tract infection, and any other symptoms requiring medical attention. Anthropometric measurements (weight and length) were performed at baseline when children were 9 months old. Weight-for-length z-score (WLZ), weight-for-age z-score (WAZ) and length-for-age z-score (LAZ) were calculated. Data on feeding practices and child dietary intake were collected at baseline using a food frequency questionnaire. Demographic and socioeconomic data were collected within 2 weeks after enrolment.

A total of 3 402 children were initially contacted, of whom 3 220 eligible children of consenting families were enrolled in the study. Of these, 2 435 children resided in randomly assigned intervention communities. The present dose–response trial aimed to determine the optimal amount of zinc to include in SQ-LNS for the prevention of common childhood infections. No impact was found of adding either 5 or 10 mg zinc to the daily portion of SQ-LNS, or of providing 5 mg zinc/day as a dispersible tablet on the incidence, longitudinal prevalence or duration of diarrhoea, malaria, fever or respiratory tract infections in children 9–18 months of age, compared with SQ-LNS without zinc. It was previously reported from this study subjects that 35.2% of the children had initial plasma zinc concentrations <65 mg/L, and there was a high prevalence of stunting, so the study population did have a high risk of zinc deficiency. Inadequate zinc absorption from SQ-LNS and insufficient adherence to the dispersible tablets were described as possible explanations for the absence of any detectable effects of additional zinc in the study population. There was no evidence to suggest that the addition of 5 or 10 mg zinc to SQ-LNS produced adverse effects. There was no increase in the incidence, prevalence or duration of any of the diseases of interest in the LNS-Zn5 or LNS-Zn10 groups compared with the negative and positive control groups.

In this well conducted and reported community-based, double-blind, placebo-controlled, cluster randomised trial, no evidence of an effects of different amounts and sources of zinc on the frequency of diarrhoea, malaria, fever and respiratory tract infections (RTI) in young children could be observed, although a large portion of the participants were diagnosed to be zinc deficient. However, it could not be ruled out that inadequate zinc absorption from SQ-LNS and insufficient adherence to the dispersible tablets are possible explanations for the absence of any detectable effect.

In a double-blind cross-over trial 47 healthy volunteers (26 females and 21 men) ingested zinc sulphate capsules containing 220 mg zinc sulphate, three times a day with each meal (resulting in a total daily dose of 150 mg Zn which equals approximately 2.1 and 2.5 mg Zn/kg bw /day for males and females, respectively) for six weeks. Plasma zinc and copper levels, plasma cholesterol, plasma low-density-lipoprotein (LDL) and high-density-lipoprotein (HDL) cholesterol, serum ceruloplasmin and erythrocyte superoxide dismutase (ESOD) were determined. In 84% of the women and 18% of the men symptoms were reported which included headaches, nausea, vomiting, loss of appetite and abdominal cramps. The study authors reported that the gastric discomfort went together with lower body weights and taking the capsules with small meals (breakfast or morning tea) or no food. Plasma zinc levels rose significantly in both men and women (36% and 57%, respectively). Plasma copper levels did not change significantly. Total plasma cholesterol and HDL were unchanged in both sexes. In females the LDL cholesterol decreased significantly from 2.38 to 2.17 mmol/L. In females a decrease was also found in serum ceruloplasmin (13% reduction) and in ESOD (20% reduction) (Samman and Roberts, 1987, 1988). The symptoms described in this study could not be observed in the other investigations available, even when the zinc dose was partly higher.

Hooper et al. (1980) examined the effect of oral zinc administration on human lipoprotein values. Twelve healthy adult men were given oral doses of 440 mg zinc sulphate/day (equals approximate 2.3 mg Zn/kg bw/day in the form of two zinc sulphate capsules containing 220 mg zinc sulphate (80 mg elemental zinc per capsule resulting in a total daily dose of 160 mg Zn), each capsule to be eaten with a main meal for 35 days. Fasting lipid levels were determined on a weekly basis and continued two weeks after zinc supplementation stopped, with a final determination at 16 weeks after start of the experiment. HDL cholesterol levels were decreased by 25% at the 7th week, but had returned to baseline levels at 16 weeks. Total serum cholesterol, triglyceride and LDL cholesterol levels were not changed. There is a discrepancy between the dosimetric data in the Samman and Roberts study (1987/1988) as compared to the Hooper et al. study (1980). In the first study, a daily dose of 660 mg zinc sulphate was declared to be equivalent to a dose of 150 mg Zn per day, while in the second study a daily dose of 440 mg zinc sulphate was stated to have resulted in a daily dose of 160 mg Zn. This discrepancy can only be explained by assuming that in the Samman and Roberts study zinc sulphate was administered in the form of the heptahydrate, while in the Hooper et al. study the monohydrate has been used. As this is not clearly stated in either of the two studies, the dosimetric data which are presented here are the same as those given in the respective publications.

Chandra (1984) examined the effect of zinc on immune response and serum lipoproteins. Zinc sulphate was administered twice daily for six weeks to 11 adult men for a total (extra) intake of 300 mg elemental zinc/day (i.e., approximately 4.3 mg Zn/kg bw/day). Dietary zinc intake amounted to ca 11 mg/person/day. No side effects were observed in any of the volunteers. After four and after six weeks of treatment, there was a significant increase in the serum zinc level and a reduction in lymphocyte stimulation response to phytohaemagglutinin (PHA). A slight increase of LDL with a simultaneous significant decrease in HDL cholesterol level was observed.

In two studies, the side-effects of zinc administration as a medication in the treatment chronic leg ulcers were investigated. In a double-blind trial, 13 humans received 200 mg zinc sulphate (i.e., approximately 135 mg Zn) three times a day for 18 weeks, while 14 humans received a placebo. No signs of nephrotoxicity associated with the zinc treatment were reported, but the study was not sufficiently documented to fully appreciate the relevance of its result (Hallbook and Lanner, 1972). In a study of Greaves and Skillen (1970) no indications for haematotoxicity, hepatotoxicity or nephrotoxicity, was determined by several clinical biochemical and haematological parameters, were seen in 18 humans after administration of 220 mg zinc sulphate (i.e., approximately 150 mg Zn) 3 times a day for 16-26 weeks.

In a 12-week double blind study Black et al. (1988) administered zinc gluconate tablets to 2 groups of healthy male volunteers for 12 weeks at doses equivalent to 50 or 75 mg zinc/kg bw/day (i.e., approximately 0.71 and 1.1 mg Zn/kg bw/day). A control group received a placebo tablet. No changes in serum cholesterol, triglyceride, and LDL and very-low-density-lipoprotein (VLDL) cholesterol levels were observed.

In a 10-week single-blind oral study conducted by Yadrick et al., (1989), 9 healthy female volunteers were given 50 mg Zn/day in form of zinc gluconate (i.e., approximately 0.83 mg Zn/kg bw/day) and 9 other healthy female volunteers were given 50 mg Zn /day plus (as zinc gluconate) 50 mg iron (as iron sulphate monohydrate) in two daily doses via their diet to investigate the effect of zinc supplementation on iron, copper and zinc status. The subjects served as their own controls. In both groups the erythrocyte superoxide dismutase (ESOD) activity was significantly reduced with 47% after 10 weeks. In the zinc supplemented group, significant decreases in haematocrit (by 4%) and serum ferritin levels (with 23%) were seen after 10 weeks, whereas the haemoglobin levels were unchanged. In the zinc iron supplemented group, serum ferritin levels were significantly increased by approximately 25%, whereas the haematocrit and haemoglobin levels were unchanged. The ceruloplasmin concentration, another indicator for copper status besides ESOD, was not altered in both groups, but the serum zinc concentration was significantly increased. The NOAEL in this study was less than 0.83 mg Zn/kg bw/day.

A significant decrease of 15% in ESOD activity was reported by Fischer et al., (1984) who administered 50 mg Zn /day in form of zinc gluconate (i.e., approximate 0.71 mg Zn/kg bw/day) divided in two daily doses to 13 healthy young men with assumed mean body weight of 70 kg for 6 weeks in a double-blind study design. The other two indices of copper status, i.e. the ceruloplasmin activity and plasma copper levels were not changed compared to the controls at 2, 4 or 6 weeks, but the serum zinc levels were significantly increased from 2 weeks of supplementation onwards. Serum zinc showed a significant inverse correlation with ESOD activity at 6 weeks.

In a controlled metabolic-unit study by Davis et al., (2000), various indicators of zinc status were measured in 25 healthy postmenopausal women (50–76, average age 64.9 years) to evaluate the usefulness of these indicators as a marker for the functional assessment of zinc status in humans. The subjects were kept under close supervision for 200 days, divided into two 90-day dietary periods, each preceded by a 10-day equilibration period. The subjects received a daily diet with a total energy content of 8.4 MJ (or 2000 kcal). In the equilibration periods the subjects received a diet containing 2 mg copper/day and 9 mg zinc/day. For the 90-day dietary periods the subjects were randomly divided into two groups, one group (n=12) was fed a low copper diet (1 mg Cu/day) and the other group (n=13) a high copper diet (3 mg Cu/day). In the first 90-day dietary period both groups received no zinc supplement (low zinc; 3 mg Zn/day), while in the second 90-day dietary period both groups received a zinc supplement of 50 mg per day (high zinc; 53 mg Zn/day). Zinc was supplemented as zinc gluconate and copper as cupric sulphate. Blood samples were taken (after overnight fasting for 12 hours) during each of the equilibration periods and one to twice monthly during the dietary periods, and analysed for various zinc-status indicators. Zinc concentrations in erythrocytes and erythrocyte membranes, plasma and erythrocyte membrane alkaline phosphatase activities, and erythrocyte membrane 5’nucleotidase activity did not change statistically significantly with the different dietary treatments. Zinc supplementation significantly increased plasma zinc concentrations and activities of mononuclear 5’nucleotidase and extracellular superoxide dismutase (P<0.0001). For all three indicators the effect of zinc supplementation was dependent on the copper intake although this was not statistically significant for plasma zinc. In case of mononuclear 5’nucleotidase activity, the difference caused by zinc supplementation was apparent when subjects were fed high dietary copper (92% change) but not when they were fed low dietary copper (5% change). The effects for plasma zinc and for extracellular superoxide dismutase activity were more apparent when subjects were fed low dietary copper (35 vs. 22% and 21 vs. 8% change, respectively). Independent of copper intake, zinc supplementation caused relatively small increases in free thyroxin (7-8%) and triiodothyronine (7-9%) concentrations, platelet zinc concentrations (10-13%) and bone specific alkaline phosphatase activity (18%) (0.002<P<0.08). The levels of the affected indicators were elevated from the equilibration values at all dietary treatments, with the exception of extracellular superoxide dismutase activity at low copper/low zinc, mononuclear 5’nucleotidase activity at low copper/low zinc, low copper/high zinc and high copper/low zinc, and thyroxin and triiodothyronine concentrations at all dietary treatments. Plasma zinc concentrations were within the normal range for healthy adults (10.7-18.4 mol/L) throughout the low zinc period, but during zinc supplementation 8 out of 23 subjects had plasma zinc concentrations >18.4 mol/L.
Decreased activities upon zinc supplementation were found for plasma 5’nucleotidase activity (P<0.0001), thyroid stimulating hormone concentrations (P<0.07) and erythrocyte superoxide dismutase activity (ESOD; not statistically significant). For these three indicators the decrease was somewhat more apparent when fed high dietary copper (28 vs. 29%, 5 vs. 9%, and 3 vs. 5%, respectively). However, for plasma 5’nucleotidase and ESOD the levels at high dietary copper were higher than at low dietary copper (only at high copper/low zinc the levels were elevated from equilibration values). For thyroid stimulating hormone the levels were depressed from equilibration values at all dietary treatments. Limited data suggested that zinc supplementation in combination with low dietary copper depresses amyloid precursor protein expression in platelets (Davis et al., 2000).

In the same dietary experiment as described by Davis et al., (2000) other parameters (i.e. copper-status and iron-status indicators) were investigated to study the effect of moderately excessive and deficient intakes of zinc on copper metabolism and utilization in humans fed low and luxuriant amounts of copper (Milne et al., 2001). For that purpose, urine and faeces were collected during the last 78 days of each 90-day dietary period and copper and zinc were determined (in faeces in 6-day composite samples). Once weekly blood was sampled (after overnight fasting for 12 hours), and blood samples were analysed for various copper-status and iron-status indicators. Women fed low copper were in negative copper balance. Zinc intake (low or high) did not alter this. Women fed high copper were put into negative copper balance by low zinc. Upon transition to high zinc, women fed high copper came into positive copper balance, which apparently was the result of a lower amount of dietary copper lost in the faeces; urinary copper was not affected. The zinc balance reflected dietary zinc intake (more positive with increased zinc intake) and was not significantly affected by copper intake.
Copper-status indicators were variably affected by dietary treatment. The concentrations of serum ceruloplasmin (enzymatically determined), HDL and VLDL cholesterol, triglycerides and red blood cell zinc did not change statistically significantly with the different dietary treatments.
Independent of zinc intake, plasma copper concentrations were significantly lower on low dietary copper than on high dietary copper (P<0.07). Although plasma copper concentrations were depressed from equilibration values at all dietary treatments, the depression was less for high than for low dietary copper (P<0.03).
Independent of copper intake, zinc supplementation caused increases in the concentrations of serum ceruloplasmin (immunochemically determined; 4-8%, P<0.05) and plasma zinc (19-32%, P<0.0001) and in platelet cytochrome c oxidase activity (on a platelet number basis; 19-27%, P<0.0007), and decreases in the concentrations of red blood cell copper (8-16%, P<0.0008) and whole blood glutathione (8-12%, P<0.009) and in the activities of specific ceruloplasmin (defined as the ratio between enzymatic and immunoreactive ceruloplasmin; 8-11%, P<0.0003) and erythrocyte glutathione peroxidase (11-15%, P<0.002). The levels of these indicators were elevated from equilibration values at all dietary treatments, with the exception of serum immunoreactive ceruloplasmin concentration (reduced at all dietary treatments), platelet cytochrome c oxidase activity (reduced at high copper/low zinc), specific ceruloplasmin activity and whole blood glutathione concentration (essentially at equilibration values at low copper/high zinc and high copper/high zinc), and red blood cell copper concentration (essentially at equilibration value at low copper/low zinc and reduced at low copper/high zinc).

Zinc supplementation significantly decreased ESOD activity (5-7%, P<0.03) as well as the concentrations of total cholesterol (3-4%, P<0.005) and LDL cholesterol (2-6%, P<0.003), but not by much. The effect on ESOD was dependent on copper intake (P<0.0001): compared to equilibration values, ESOD activity decreased on low copper but increased on high copper. Total cholesterol and LDL cholesterol concentrations were significantly higher on low dietary copper than on high dietary copper (P<0.02 and P<0.03, respectively). This suggests a dependency on copper intake, but it should be noted that women fed low copper had higher equilibration values for both indicators than women fed high copper. The authors stated that measured indicators of iron status (serum iron, haemoglobin, haematocrit and percent transferrin saturation) were unaffected by dietary treatment (no data presented), with the exception of haemoglobin, which was lower on high zinc than on low zinc in both the low and high copper groups. The drop in haemoglobin occurred especially during the last month of zinc supplementation, possibly due to the frequent blood sampling. Data from another two volunteers (one on a low copper diet and one on a high copper diet) were not included, because they were using an adhesive containing extremely high amounts of zinc for their false teeth.

 

Epidemiological studies, RDT oral exposure - Case-control studies
Mahabir et al. 2006 conducted an evaluation in an ongoing case–control study in which the associations between dietary and supplemental intakes of zinc, selenium and copper, and the risk for lung cancer was investigated.

The study population consisted of 1 676 patients (recruited from The University of Texas M. D. Anderson Cancer Center, Houston) with lung cancer (cases) and 1 676 healthy controls selected from the control database to be frequency matched by age (>5 years). All participants completed a personal interview to obtain information on demographic factors and smoking and drinking history. History of emphysema was based on the subject reporting a physician’s diagnosis of emphysema. Family history of cancer was defined as a first-degree relative ever being diagnosed with cancer. Dietary data were collected from a modified version of the 135-item National Cancer Institute’s health habits and history questionnaire (HHHQ) and food frequency questionnaire, and nutrient intake was calculated.

Overall, cases and controls did not differ by ethnicity, but men were overrepresented in cases (53.8%) versus controls (49.5%). Cases compared to controls had fewer never smokers and former smokers, but more current smokers. Cases also reported higher pack-years of smoking than controls (p<0.0001). Cases also generally had lower BMI than controls (p<0.0001). Total caloric intake was similar in cases and controls. Overall and by gender, cases compared to controls had significantly lower dietary zinc (men: 11.08 vs. 11.67 mg/d; women: 8.73 vs. 9.09 mg/d) and copper (men: 1.32 vs. 1.43 mg/d; women: 1.10 vs. 1.18 mg/d) intakes. Differences in selenium intake were not statistically significant.

When the dietary intakes of zinc, copper and selenium were analysed separately, increasing zinc (from <7.59 to >12.31 mg/d) and copper intakes were associated with lower risk of lung cancer, whereas selenium showed non-significant risk reductions only in the highest quartile of intake. Overall, increased dietary intake of zinc was associated with a monotonically decreasing risk of lung cancer, with a 20, 36 and 43% significant reduction in risk with increasing quartile of intake. These associations were similar for both men and women, but significant only in men.

Subgroup analyses defined by age (<60 and >60 years), BMI (<25 and >25), smoking status (current, former and never smokers) and alcohol intake categories (non-drinkers, light drinkers and moderate–heavy drinkers) was conducted. There were significant (p<0.05) trends for decreased risk with increased dietary zinc intakes in both age strata. Among the younger subjects (<60 years), those in the highest quartile of dietary zinc intake had a 46% reduced risk when compared with a 40% reduced risk in older subjects (>60 years). A significant inverse trend (p 5 0.007) was observed among subjects with BMI >25, corresponding to a 21, 39 and 42% reduction in risk for the second, third and fourth quartiles of dietary zinc intake, respectively. There was a decreased risk among the lighter subjects (BMI <25), but these were not statistically significant. The protective effect of zinc was largely restricted to the current smokers, for whom the highest quartile of zinc intake was associated with a 64% reduced risk. Higher dietary zinc intake was associated with a significant trend (p =0.009) for decreased risk only in the lowest tertile of pack-years (<30) For drinking categories, a significant (p=0.0005) protective dose effect for dietary zinc intake was observed only among light drinkers. Dietary zinc intake was associated with a significant trend for reduced risk among those who did not use vitamin/mineral supplements, and borderline significant trend (p=0.09) for reduced risk among users of vitamin/mineral supplements. The highest quartile of zinc intake among nonusers was associated with a significant 69% reduced risk versus a 44% reduction in risk in users. Higher levels of dietary zinc were associated with significant trends (p<0.05) for reduced risk only among subjects who reported no prior diagnosis of emphysema.

In this study conducted in an ongoing case–control study, multiple logistic regression analysis showed that the odds ratios (OR) and 95% confidence intervals (CI) of lung cancer for all subjects by increasing quartiles of dietary zinc intake were 1.0, 0.80 (0.65–0.99), 0.64 (0.51–0.81), 0.57 (0.42–0.75), respectively; similar results were found for men. Protective trends (p<0.05) against lung cancer with increased dietary zinc intake were also found for all ages, BMI >25, current smokers, pack-years <30, light drinkers and participants without emphysema. Results suggest that dietary zinc and copper intakes are associated with reduced risk of lung cancer. This evaluation conducted in an ongoing case–control study revealed evidence of a protective effect of dietary zinc intake, in combination with copper (and selenium) against lung cancer by increasing levels of zinc intake in a case-control study. The study supports the evidence of a protective role of adequate zinc levels with respect to the risk of lung cancer.

 

 

Epidemiological studies, RDT oral exposure - Cohort/Longitudinal studies
The cohort (longitudinal) study by Pilz et al. 2008 was designed to evaluate whether low zinc concentrations are associated with total, cardiovascular and non-cardiovascular mortality in patients referred to coronary angiography.

The LURIC study was designed to evaluate the environmental and genetic risk factors for atherosclerosis and related metabolic diseases. Baseline examinations were performed from July 1997 to January 2000 and included 3316 Caucasians who were referred to coronary angiography at the Heart Centre of the Ludwigshafen General Hospital, Southwest Germany. Inclusion criteria were clinical stability with the exception of acute coronary syndromes, the availability of a coronary angiogram and German ancestry. Blood collection was performed after a 10–h overnight fast in the early morning before coronary angiography. Routine clinical parameters were measured immediately. Serum zinc concentrations were determined as part of the baseline measurements on a weekly basis. N-terminal pro-B-type natriuretic peptide, an established and clinically used parameter to assess cardiovascular risk and myocardial dysfunction, and high-sensitive C-reactive protein, retinol and a-tocopherol were measured. In the follow up, information about vital status was obtained from local person registries. Medical records of local hospitals, death certificates and autopsy data were used to classify the causes of death into cardiovascular and non-cardiovascular.

Zinc values were available in all 3 316 subjects and baseline characteristics were stratified by serum zinc in 4 quartiles (<780 µg/l to >960 µg/l). Beer and wine consumption evaluated by a questionnaire at baseline (four categories: never, sometimes, regular and often) were not significantly associated with serum zinc quartiles. 2.4% of the present study subjects took vitamin supplements and their serum zinc concentrations were not significantly different when compared with the other study subjects.

Eighteen patients were lost during the follow-up period and were therefore excluded from the analyses. In the remaining study cohort of 3 298 patients, 769 (23% of the study population) had died, after a median time of follow-up of 7.75 years. In 24 of the deceased patients, sufficient information to classify their causes of death could not be obtained and they were thus included in the analyses for total mortality but excluded from the analyses for cardiovascular and non-cardiovascular mortality. From the 3 274 study participants who were followed up for differentiated mortality analyses, 484 (15%) died due to cardiovascular causes and 261 (8%) due to non-cardiovascular causes. Statistical analysis revealed that the risk for total, cardiovascular and non-cardiovascular mortality significantly increased across serum zinc quartiles (P<0.001) with lowest cumulative survival in the first quartile.

Unadjusted hazard ratios (HR) for total mortality for the first compared with the fourth zinc quartile (HR set to 1.0 as reference) and the per quartile decrease were 2.36 (CI 1.91-2.92; P<0.001) and 1.35 (CI 1.26-1.44; P<0.001), respectively. Accordingly, unadjusted HR were 2.12 (CI 1.63-2.77; P<0.001) and 1.30 (CI 1.19-1.41; P<0.001) for cardiovascular mortality and 3.09 (CI 2.11-4.52; P<0.001) and 1.49 (CI 1.33-1.68; P<0.001) for non-cardiovascular mortality. HR for total and cardiovascular mortality remained highly significant even after adjustment for several possible confounders. In the analyses of cardiovascular mortality, significance was lost when the first was compared with the fourth zinc quartile in the fully adjusted model but remained significant for decreasing zinc quartiles as a continuous variable (p=0.038). Unadjusted and fully adjusted (according to model 3) HR of individuals with serum zinc concentrations below 700 mg/l (n=379) compared with those in the fourth zinc quartile (<960 µg/l) were 3.12 (CI 2.46-3.95; P<0.001) and 2.03 (CI 1.54-2.68, P<0.001) for total mortality, 2.85 (CI 2.12-3.84, P<0.001) and 1.50 (CI 1.04-2.17, P=0.030) for cardiovascular mortality and 3.97 (CI 2.60-6.05; P<0.001) and 3.22 (CI 1.97-5.27, P<0.001) for non-cardiovascular mortality.

In this large, well-defined cohort study in patients referred to coronary angiography, zinc deficiency at baseline was associated with total, cardiovascular and non-cardiovascular mortality. After careful adjustments for several cardiovascular risk factors and possible confounders related to zinc metabolism, low serum zinc concentrations remained an independent and highly significant predictor for total and non-cardiovascular mortality.

Mortality analyses was carefully adjusted for several factors that may contribute to the reduced zinc concentrations in the ageing population (low dietary intake, malabsorption or comorbidities e.g. inflammatory and metabolic diseases) in order to reduce the probability that the association between zinc and mortality was only observed due to medical conditions with a secondary decline of serum zinc concentrations, a process that might partially occur due to a redistribution of plasma zinc to other tissues (e.g. in inflammatory diseases). However, low serum zinc remained a significant predictor of mortality even after these adjustments, suggesting that zinc deficiency may directly contribute to a reduced life expectancy.

In a large, well-defined cohort study in patients referred to coronary angiography, evidence was found that zinc deficiency was associated with mortality (total, cardiovascular and non-cardiovascular). This was also seen when adjusted was conducted for several confounding factors. The results of this study support the evidence that low serum zinc levels may directly contribute to a reduced life expectancy not only in the patient population investigated in this study and contribute to the evidence of a protective role of adequate zinc levels with respect to life expectancy.

 

Epidemiological studies, RDT oral exposure - Cross-sectional studies
In this cross-sectional epidemiological study by Feng et al. 2015, the potential association between 23 urinary metals and altered heart rate variability (HRV) among residents of an urban community in Wuhan, China was examined.
A cross-sectional analysis of 23 urinary metals and 5-min HRV indices (SDNN, standard deviation of normal-to-normal intervals; r-MSSD, root mean square of successive differences in adjacent normal-to-normal intervals; LF, low frequency; HF, high frequency; TP, total power) using baseline data from a prospective cohort study conducted from April 2011 through May 2011 was conducted on 2 004 adult residents of Wuhan.

Of 3 698 invited community residents, 3 053 (82.6%) individuals agreed to participate in qualitative face-to-face interviews and physical examination and provided baseline blood and urine samples and questionnaire data concerning demographic information, occupational and environmental exposures, family and personal diseases, medication use, smoking, alcohol use, diet, and socioeconomic status. Several individuals were excluded, and the final study sample consisted of 2 004 individuals.

Spot urine samples were collected from participants and stored frozen until analysis for urinary metals and creatinine within 6 months. HRV indices of participants were measured after urine sample collection. Five measures of HRV including both time and frequency domain outcomes were included in this analysis. The time domain variables included the standard deviation of all normal R-R intervals (SDNN) and the root mean of square of successive differences between adjacent normal NN intervals (r-MSSD). The frequency domain parameters included low-frequency power (LF, 0.04–0.15 Hz), high-frequency power (HF, 0.15–0.40 Hz), and total power (TP, 0.01–0.40 Hz).

The 10-year Framingham risk score (FRS) values were calculated for each individual using age, sex, low-density lipoprotein (LDL), high-density lipoprotein (HDL), blood pressure, diabetes, and smoking status.

The distribution of the 23 urinary metals (standardized and unstandardized for urinary creatinine) revealed that tin, tungsten, and lead concentrations were <LOQ in 37.13%, 2.15%, and 5.39% of samples, respectively, and <0.5% of samples were <LOQ for chromium, cobalt, nickel, and uranium. Concentrations of all other metals were ≥LOQ in all samples. The limits of quantification (LOQ) for the urinary metals were in the range 0.0004–0.292 μg/L. Spearman’s rank correlation analysis revealed that all 23 metals were positively and significantly associated with each other (all p<0.001).

After adjusting for other metals, creatinine, and other covariates, natural log-transformed urine titanium concentration was positively associated with all HRV indices (all p<0.05). Moreover, negative associations between cadmium and r-MSSD, LF, HF, and TP were estimated; between lead and r-MSSD, HF, and TP; and between iron, copper, and arsenic and HF, SDNN, and LF, respectively, based on models adjusted for other metals, creatinine, and covariates (all p<0.10). Several associations differed according to cardiovascular disease risk factors. For example, negative associations between cadmium and r-MSSD were stronger among participants ≤52 years of age (vs. >52), current smokers (vs. nonsmokers), body mass index <25 kg/m2 (vs. ≥25), and among those who were not hypertensive.

In the single-metal linear regression models adjusted for age, sex, smoking status, pack-years, BMI, hypertension, hyperlipidemia, diabetes, and urinary creatinine, titanium, and chromium were positively associated with one or more HRV indices, whereas aluminium, manganese, iron, cobalt, copper, zinc, cadmium, antimony, barium, lead, and uranium were negatively related to one or more HRV parameters (all p<0.05). However, only the associations of manganese, iron, and copper with HF were significant after FDR-adjustment at the 5% alpha level. Zinc was negatively correlated with SDNN, r-MSSD, low frequency and high frequency in the single-metal linear regression models, but the total power was low and the values did not reach statistical significance.

In this cross-sectional epidemiological study population, urine concentrations of several metals were associated with HRV parameters. Zinc was detected below the LOQ, and zinc was negatively related to several HRV parameters, but did not reach statistical significance.

In this epidemiological study, there was no consistent correlation between zinc with several HRV parameters between single and multiple-metal analyses.

In this cross-sectional epidemiological study by Hennigar et al. 2018, serum zinc concentrations in the US population were evaluated to determine factors affecting serum zinc with the use of NHANES (National Health and Nutrition Examination Survey) 2011–2014.
Serum zinc concentrations in the US population were evaluated by the use of NHANES 2011–2012 and 2013–2014 data. Serum zinc data from those individuals aged ≥6 y participating in NHANES 2011–2014 with serum zinc values (approximately one-third of the sample) were used for these analyses. Data for pregnant (n=34) or lactating (n=20) females were analysed separately. The final analytic sample of those aged ≥6 y excluding those who were pregnant, or lactating was 4 347 participants.

Dietary zinc intake was determined, and factors affecting serum zinc were identified with the use of regression models adjusting for sex, age, fasting status, and time of blood draw. ORs were calculated to identify factors associated with the risk of being below the serum zinc cutoff, and the prevalence of low serum zinc in the US was calculated.

Mean dietary and total daily zinc (dietary + supplemental zinc) intakes were at or above the (Estimated Average Requirement) RDA for zinc for all age groups. Children aged 6–8 y consumed approximately twice the RDA for zinc, with the majority of zinc derived from dietary sources. Mean dietary zinc intake in males increased from 11.8 mg/d in those aged 9–13 y to 14.0 mg/d in those aged 19–30 y (P < 0.01) and declined thereafter to 12.0 mg/d in those aged ≥71 y (compared with age 19–30 y, P < 0.01). Mean dietary zinc intake in females did not follow a discernible pattern and varied only slightly across age groups, with a 0.6-mg/d difference between the highest (age 19–50 y) and lowest (ages 14–18 y and ≥71 y) intakes. Mean total daily zinc intake was higher in males than in females (17.3 ± 0.3 and 13.4 ± 0.4 mg/d; P<0.0001) and tended to increase with age in both males and females, from 12.7 to 21.6 mg/d in males and from 10.1 to 14.9 mg/d in females aged 9–13 y compared with those aged ≥71 y (P < 0.01). Pregnant and lactating women consumed less than the RDA for zinc from diet alone; however, both groups consumed approximately twice the RDA with the addition of zinc from supplements.

Serum zinc concentrations were higher in males than in females (P<0.0001). Mean ± SE serum zinc concentrations in males and females were 84.9 ± 0.8 and 80.6 ± 0.6 μg/dL, respectively. Overall, there was no difference in serum zinc in those aged 6–9 y compared with those aged ≥10 y. When separated on the basis of sex and age, serum zinc concentrations increased in males from early childhood to age ∼30 y and declined thereafter with increasing age, but this trend was not significant. Serum zinc concentrations in females were not affected by age. Ethnicity, poverty-income ratio, physical activity, diabetes, and smoking or alcohol use did not affect serum zinc concentrations.

Serum zinc concentrations were 9% lower in afternoon blood draws (P<0.01) and declined even further in evening blood draws (P<0.01) compared with non-fasting morning blood draws; no difference was observed between fasting and non-fasting morning samples. Participants with hypoalbuminemia (serum albumin ≤3.5 g/dL) and females with anaemia (haemoglobin ≤12 g/dL) had significantly lower serum zinc concentrations (P<0.0001 for both). High white blood cell count, hormone or steroid use, and BMI and waist circumference were not associated with serum zinc levels; there was no difference in serum zinc concentrations when the population (male or female) was divided into those consuming less than or greater than the RDA for zinc from diet, supplements, or total zinc.

Pregnant women had lower serum zinc concentrations (P<0.0004) than did age-matched, non-pregnant women. Lactating women had 6% lower serum zinc concentrations; however, due to the low sample size (n=20), this was not significantly different from age-matched, non-lactating women. Serum zinc concentrations did not differ in oral contraceptive users compared with nonusers.

Regression models with serum zinc as the dependent variable indicated that afternoon and evening blood draws (P<0.0001) were negatively associated with serum zinc concentrations and serum albumin (P<0.0001) and haemoglobin (P=0.0048) were positively associated with serum zinc concentrations. Hypoalbuminemia, anaemia in females and pregnancy increased the odds of being below the serum zinc cutoff (P<0.0001) for all. Approximately 3.8% of children (<10 y), 8.6% of males (≥10 y), and 8.2% of females (≥10 y) were below the serum zinc cutoff (children aged <10 y: morning/nonfasting, 65 μg/dL; afternoon 57 μg/dL; females aged ≥10 y: morning/fasting, 70 μg/dL; morning/nonfasting, 66 μg/dL; afternoon, 59 μg/dL; and males aged ≥10 y: morning/fasting, 74 μg/dL; morning/nonfasting, 70 μg/dL; afternoon, 61 μg/dL)

In this epidemiological study on serum zinc concentration in the US population and factors influencing serum zinc levels it was demonstrated that mean serum zinc concentrations were significantly higher in males than in females. Regression models with serum zinc as the dependent variable indicated that afternoon and evening blood draws were negatively associated with serum zinc concentrations and serum albumin and haemoglobin were positively associated with serum zinc concentrations. Hypoalbuminemia, anaemia in females, and pregnancy increased the odd ratio of being below the serum zinc cutoff. Zinc from diet or supplements did not affect serum zinc. Approximately 3.8% of children (<10 y), 8.6% of males (≥10 y), and 8.2% of females (≥10 y) were below the serum zinc cutoff.

This epidemiological study provides an overview on serum zinc levels in the US population and shows that zinc intake from diet or supplementation did not affect serum zinc concentrations in the general population. It was also shown that hypoalbuminemia, anaemia in females, and pregnancy decreased serum zinc levels below the serum zinc cutoff levels recommended by international organizations of supporting the role of adequate zinc homeostasis for the health in specific population subgroups.
Materials and methods as well as results are appropriately described and presented in the publication.

This cross-sectional epidemiological study by Ihedioha et al. 2014 in the Nigerian population was conducted to assess the health risk of zinc, chromium, and nickel from cow meat consumption. Dried meat samples were digested and zinc, chromium, and nickel concentrations were determined with atomic absorption spectrophotometer. Daily intakes of meat were obtained using a semi-quantitative food frequency questionnaire (FFQ) and applied to 755 subjects (adult men and women, pregnant/lactating women, undergraduate students, and school children) between 2007 and 2010.

Weekly intakes of beef consumption were estimated for each subject based on participant body weight data measured by using a bathroom balance. Estimated daily intakes (EDI) of the metals were calculated, and the health risks from consumption of cow meat were assessed using the target hazard quotient (THQ), which is the ratio of determined dose of a pollutant to a reference dose level.

In the meat samples, the highest concentration of zinc was observed in liver, followed by muscle. The lowest concentration of zinc was measured in intestine samples. The highest total daily consumption rate of cow meat was recorded for pregnant/lactating women while the lowest consumption rate was recorded for school children. For adult men, tripe was the most important source of zinc followed by intestine. For undergraduate students, muscle was the largest source of zinc and for schoolchildren it was liver.

The total daily intakes (µg/person/day) of zinc, nickel, and chromium from cow meat consumption were highest for pregnant/lactating women and lowest for schoolchildren. The estimated daily intakes (EDI) ranges for zinc were 10 496–13 459 µg/person/day. Estimated daily intake for zinc was 15–30% of provisional maximum tolerable daily intake (PMTDI: 1000 mg/kg body weight). The THQs for zinc were: adult men (0.56), adult women (0.57), pregnant/lactating women (0.47), undergraduate students (0.58), and schoolchildren (0.96) indicating no health risk.

In this epidemiological study in the Nigerian population to assess the health risk of zinc, chromium, and nickel from cow meat consumption, it was shown that the estimated daily intake for zinc was 15–30% of provisional maximum tolerable daily intake, and the target hazard quotient (THQ) for zinc were within WHO/FAO limit. There was no evidence of possible health risk to consumers with regard to zinc (and nickel). Chromium intakes were above recommended daily intake (RDI).

The results of this epidemiological study to assess the health risk of metals including zinc showed that intake of zinc from meat consumption results in levels within the recommended limits of international organizations and were not associated with a health risk.
Materials and methods as well as results are appropriately described and presented in the publication.

 

In this cross-sectional epidemiological study by Jung et al. 2015 in subjects from the rural areas of South Korea, the cross-sectional relationships of inflammatory markers with dietary zinc intake and serum zinc levels was investigated in healthy men and women aged 40 and older.

A group of 1 055 subjects (404 men, 651 women) was included in dietary zinc analysis while another group of 695 subjects (263 men, 432 women) was included in serum zinc analysis. Serum cytokines (IL-6, TNF-α) and CRP were measured as inflammatory markers.

Average zinc intake calculated from food frequency questionnaire (FFQ) were 9.6 mg/d for men and 8.0 mg/d for women on the study population. Serum zinc level of the present study subjects were 89.9–119.9 μg/dL for men and 91.8–118.3 μg/dL for women of the Korean population. There was no correlation between dietary zinc intake and serum zinc levels. Inflammatory markers were not associated with dietary zinc intake but showed significant inverse associations with serum zinc levels. A significant relation between serum zinc levels with all three inflammatory markers (IL-6: p=0.0236, TNF-α: p=0.0017, and CRP: p=0.0301) was found in women. In men only IL-6 (p=0.0191) was significantly associated with serum zinc levels showing an inverse linear trend, and CRP was lowest in the highest tertile of serum zinc level, and there was no relation for TNF-α. Serum zinc had only a small contribution to total variation of all inflammatory markers (<10%).

In this epidemiological study in the Korean population, it could be demonstrated that serum zinc levels may inversely be related to inflammatory markers (IL-6, TNF-α, and CRP). A relatively stronger linear trend between serum zinc levels and inflammatory markers was found in women than in men. Although, no significantly different results of the dietary zinc intake in relation to inflammatory markers were observed, the results indicate that serum zinc levels could be partially responsible for lower inflammation processes in terms of acute inflammation. However, no causal relationship between zinc status and inflammatory markers could be obtained from this cross-sectional study.

This epidemiological study in subjects from the rural areas of South Korea showed some, although weak, evidence that serum zinc levels could be partially responsible for lower acute inflammatory processes, particularly in woman. The study supports the evidence of a protective role of adequate zinc levels with respect susceptibility to inflammatory markers in the study population.
Materials and methods as well as results are appropriately described and presented in the publication.

 

In this cross-sectional epidemiological study by Kim et al. 2018 investigated the association between mineral intake (calcium, phosphorus, sodium, potassium, iron, and zinc) and chronic kidney disease (CKD) by using the Korean Health Examinee (HEXA) cohort data.

The Health Examinee (HEXA) cohort of the Korean Genome and Epidemiologic Study (KoGES) was used for the study. Mineral intake was assessed by a food frequency questionnaire for 159 711 participants. CKD was defined as an estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m2. Dietary intake of each mineral was divided into quartiles and the quartile including recommended dietary allowance (RDA) or adequate intake (AI) of each mineral was used as a reference. The association between the quartile of mineral intakes and CKD was assessed by using polytomous logistic regression models.

Height and weight were measured, and body mass index (BMI) was calculated. Blood pressure was measured with sphygmomanometers after rest. Blood and urine samples were obtained from each participant after >8 h of fasting and serum creatinine levels were determined.

Of the 159 711 participants, 3 053 (1.9%) were classified as having CKD. Participants with CKD were more likely to be older, male, smokers who exercised more, were single (unmarried), had lower education levels (below middle school), had a monthly household income lower than 1 500 000 KRW, lower protein and total cholesterol levels, and a history of hypertension and diabetes mellitus.

When the mineral intake was divided into quartiles, the lowest quartiles of mineral intake (<5.86 mg/day for zinc) were associated with increased odds of advanced CKD compared with the reference quartiles (the third-highest quartile for zinc: 7.38–9.35 mg/day), which included values for the recommended dietary allowance (RDA) or adequate intake (AI), for phosphorus, potassium, iron, and zinc (OR = 1.52; 95% CI: 1.02–2.26).

When the analysis was stratified by hypertensive and non-hypertensive groups, the associations between mineral intake and CKD were only observed in the hypertensive groups. This result also showed that 5 126 subjects had diabetes mellitus among the hypertensive patients. However, when the analysis was stratified by diabetes mellitus status, the associations between mineral intake and CKD were observed in both diabetes mellitus and non-diabetes mellitus groups, and the patterns of the association were similar.

In this epidemiological study using the Korean Health Examinee (HEXA) cohort data, the lowest quartiles of phosphorus, potassium, iron and zinc were associated with higher odds for advanced CKD compared with the references. The present study suggests that an inadequate intake of some minerals (including zinc) may be associated with CKD occurrence in the general population.

This epidemiological study in subjects from the Korean Health Examinee (HEXA) cohort showed evidence that serum zinc levels (beside other minerals) below the reference values were associated with a risk of CKD in the general population. The study supports the evidence of a protective role of adequate zinc levels with respect susceptibility to CKD in the general population. Materials and methods as well as results are appropriately described and presented in the publication.

 

In this cross-sectional epidemiological study by Yang et al. 2010, a cross-sectional analysis of a prospective cohort baseline study was performed to evaluate the relationship between dietary Zn intake and the risk of atherosclerosis in adult Koreans free of clinical cardiovascular disease (CVD).

The Korean Multi-Rural Communities Cohort Study in was initiated in 2004 to construct a genomic cohort and identify risk factors for CVD. As baseline, 7 818 subjects aged >40 years were recruited from the centres located in Yangpyeong, Namwon and Goryeong between January 2005 and November 2007. A total of 4 564 subjects aged 40–89 years were included in the final data analysis.

A structured questionnaire, including information on demographics, education, smoking, alcohol intake, exercise, medical history and female reproductive history, was administered. Height and weight were measured and BMI calculated as. Waist circumference and blood pressure was measured and systolic and diastolic blood pressure were recorded. Blood samples were collected in the morning after at least 8 h of fasting, and plasma total cholesterol, TAG, glucose and HDL-cholesterol were measured on the same day, LDL-cholesterol was calculated.

Dietary data were collected using a food-based questionnaire (FFQ). Measurement of intima-media thickness (IMT) of the common carotid artery was conducted with the subject in the supine position using high-resolution B-mode ultrasound.

Men made up 40.2% of the total number of subjects. The mean ages of men and women were 61.3 and 59.7 years, respectively. The proportion of the subjects aged >65 years was 38.5% of the total number of subjects. The proportions of the subjects whose BMI was >25 kg/m2 were 31.9% of the men and 36.1% of the women, respectively. The proportion of postmenopausal women was 78.4 %. Men were more likely to have a higher education, and to be current smokers and current drinkers than women. Means of total daily energy intakes were 7261.8 kJ (1736.6 kcal) for men and 6370.7 kJ (1523.5 kcal) for women. Means of daily Zn intake for men and women were 6.1 and 6.0 mg/d after adjustment for total energy intake by the residual method.

The median Zn intakes of the first, second, third, fourth and fifth quintiles were 5.00, 5.48, 5.85, 6.29 and 7.19 mg/d, respectively. Age, total energy intake, carbohydrate and proportion of current smokers decreased across the Zn intake groups. The proportions of higher education, current drinkers, regular exercise, waist circumference, serum HDL-cholesterol, and intakes of alcohol, protein, fat, b-carotene, vitamin C, folate, vitamin E, fibre and cholesterol increased across Zn intake groups.

The middle-aged (<65 years) and the elderly (>65 years) populations showed similar median Zn intakes. Means of IMT in the elderly population were higher than those in the middle-aged population. After adjustment for age, sex, education, alcohol intake, smoking, regular exercise, waist circumference, HDL-cholesterol, dietary adjusted IMT mean in the first quintile of Zn intake group was significantly higher than that in the fifth quintile group among the total subjects.

When subclinical atherosclerosis was defined by <80th percentile value of IMT (0.8232 mm), 10.4% of the middle-aged population and 35.7% of the elderly population were classified as having subclinical atherosclerosis. After adjustment for potential confounders in the third model, Zn intake was inversely related to subclinical atherosclerosis (5th v. 1st quintile, OR 0.64, CI 0.45-0.90, P=0.069). In the middle-aged population, a significant inverse correlation between Zn intake and subclinical atherosclerosis was found in the third model (5th v. 1st quintile, OR 0.44, CI 0.26-0.76, P=0.048). However, no significant relation was found in the elderly population.

When subclinical atherosclerosis was defined by >1mm of IMT, 1.6% of the middle-aged population and 7.9% of the elderly population were classified as having subclinical atherosclerosis. Zn intake was inversely correlated with the risk of subclinical atherosclerosis after adjusting for potential confounders (5th v. 1st quintile, OR 0.34, CI 0.16-0.70, P=0.005). The elderly subjects showed an inverse relationship between Zn intake and the risk of subclinical atherosclerosis (5th v. 1st quintile, OR 0.33, CI 0.14-0.77, P=0.013). No significant correlations were found in middle-aged adult subjects.

In this epidemiological study to determine the relationship between dietary Zn intake and IMT, an indicator of subclinical atherosclerosis it could be demonstrated that after adjustment for potential confounders, the mean carotid IMT in the low Zn intake group was higher than that in the high Zn intake group, and Zn intake was inversely related to subclinical atherosclerosis. Thus. in persons free of clinical CVD, dietary Zn intake was inversely correlated with subclinical atherosclerosis. Inadequate intake of Zn was related to high IMT and high risk of subclinical atherosclerosis.

The findings of this epidemiological study suggest that adequate intake of Zn may have a beneficial effect in reducing the risk of atherosclerosis in the rural middle-aged adult and elderly populations in Korea. This study contributes to the evidence of a protective role of adequate zinc intake with respect to the risk of atherosclerosis. Materials and methods as well as results are appropriately described and presented in the publication

 

In this cross-sectional epidemiological study by Ananthakrishnan et al. 2015, Zinc intake and risk of Crohn's disease (CD) and ulcerative colitis (UC) was evaluated in two large prospective cohorts of women in the USA.

Data from 170 776 women from the Nurses Health Study I and Nurses Health Study II, who were followed for 26 years were analysed for the association between dietary and supplemental intakes of zinc and the incidence of CD and UC. The NHS I, established in 1976, recruited 121 700 female registered nurses between the ages of 30 and 55 years. The NHS II, initiated in 1989, recruited a younger cohort of 116 686 female registered nurses between the ages of 25 and 42 years at enrolment. Zinc intake was assessed using semi-quantitative food frequency questionnaires (SFFQ) administered every 4 years. Participants were also asked about consumption of multivitamins and zinc supplements including brand, dose, duration and frequency of use. Nutrient intakes were calculated by multiplying the frequency of the food consumed and the nutrient content of specific portion sizes based on tables provided by the Department of Agriculture. Nutrient intakes were adjusted for total energy intake by the residual method. Total intake of zinc included that consumed from diet and through supplements and multivitamins.

Incidents of CD and UC were ascertained by medical record review. Participants of both NHS I and NHS II were asked to self-report a diagnosis of CD or UC. Participants reporting this diagnosis were sent a supplemental questionnaire ascertaining history of disease in greater detail including date of diagnosis, disease complications and need for specific medications and surgery. The final cohort consisted of 269 incident cases of CD and 338 cases of UC. Other potential lifestyle influences on IBD including smoking, use of menopausal hormone therapy or oral contraceptives, and non-steroidal anti-inflammatory drugs were gathered biennially. Physical activity was assessed every 4 years as reported previously. Body mass index (BMI) was calculated by dividing weight by the square of height. The final cohort included 76 738 women from NHS and 94 071 women from NHS II. Over 3 317 550 person-years (p-y) of follow-up, 269 incident cases of CD (incidence 8 per 100 000 p-y) and 338 cases of UC (incidence 10 per 100 000 p-y) were identified. Zinc intake at baseline ranged from a median of 9.0 mg/day among women in the lowest quintile to 27.0 mg/day among women in the highest quintile.

There were no significant differences in age distribution across the quintiles; most women were of Caucasian ethnicity. A similar proportion of women in each quintile had a history of smoking and use of oral contraceptives or menopausal hormone replacement therapy. There was a higher proportion of women with a BMI of >30 in the highest quintile when compared with those in the lowest quintile of zinc intake. Women in the highest quintile of zinc intake also had greater protein intake but were similar in their consumption of total calories and fat and had similar levels of physical activity. Total zinc intake comprised almost exclusively dietary zinc in the lowest three quintiles of intake, whereas zinc intake from supplements comprised a larger proportion of total intake in women belonging to the highest quintile.

Women in higher quintiles of total zinc intake had reduced risk of CD. Compared with a CD incidence of 11 per 100 000 p-y in the quintile with the lowest zinc intake, the incidence of CD was 6 per 100 000 p-y in the third and fourth quintiles and 8 per 100 000 p-y in the highest quintile of intake. Adjusting for potential confounders, women in the third (HR 0.60, CI, 0.40 – 0.89), fourth (HR 0.57, CI 0.38 – 0.86) and fifth (HR 0.74, CI 0.50 – 1.10) quintiles had lower risk of CD (P=0.003). The reduction in risk with increasing zinc intake was seen up to a daily intake of 15 mg/day, after which the risk reduction reached a plateau. Compared with individuals with intake of zinc less than the recommended daily allowance (8 mg/day), those with intake of 8–16 mg/day (HR 0.69, 0.44 – 1.08) and >16 mg/day (HR 0.52, 0.32 – 0.86) had a reduced risk of CD. There was a stronger inverse association with dietary zinc intake than for zinc intake from supplements. Compared with women in the lowest quintile of dietary zinc, women in the highest quintile had a reduced risk of CD (HR 0.63, 0.43 – 0.93; P=0.04). Neither dietary zinc nor supplemental zinc intake modified risk of UC.

In this epidemiological study in in two large prospective cohorts of women in the USA it was demonstrated that compared with women with the lowest quintile of Zn intake, the multivariate hazard ratios (HR) for CD were 0.92 for women in the second quintile of intake, 0.60 for the third quintile, 0.57 for fourth quintile and 0.74 for the highest quintile. The association was stronger for dietary zinc than for zinc intake from supplements. Neither dietary nor supplemental zinc modified risk of UC.

In this cross-sectional study in woman, intake of zinc was inversely associated with risk of CD but not UC. The results of this study support the evidence that low zinc intake from the diet may increase the risk of woman for CD and contribute to the evidence of a protective role of adequate zinc levels with respect to autoimmune diseases such as CD.
Materials and methods as well as results are appropriately described and presented in the publication.

In this cross-sectional study by Nakamura et al. 2019, the association between the intake of six minerals and mental disorders was investigated in a cross-sectional study among the Japanese working population. Data from the Eating Habit and Well-being (Eat-Well) study in Japanese workers were used and a total of 2 089 individuals were included in the final analyses. A questionnaire survey for workers was conducted between December 2013 and February 2014 in employees of 43 small- and medium-sized manufacturing companies in Shizuoka, Japan. Kessler’s six-item psychological distress scale (K6) was used to detect depression and anxiety symptoms. Depression and anxiety symptoms were identified with a cut-off point of 13+ based on previous Western and Asian studies.

The validated food frequency questionnaire (FFQ) developed for Japanese adults was used to assess diet as an exposure variable. Energy and mineral intake were calculated based on the Standard Tables of Food Composition in Japan, and the energy-adjusted mineral intake was obtained by adjusting the total energy intake using a nutrient residual model. Data on smoking, alcohol drinking, work schedule (i.e., shift working or day working), medications for hypertension, hyperlipidaemia, and diabetes, and body mass index (BMI) were obtained by a self-administered questionnaire.

The prevalence of depression and anxiety symptoms identified by a K6 score of 13+ was 6.9% among the 2 089 participants, 8.1% among 1 453 men and 4.2% among 636 women. Participants with depression and anxiety symptoms (K6, 13+) were more likely to be younger and to have a lower dietary intake of minerals and vitamins. Mean zinc (copper, and manganese) intake in participants with a K6 score <13 was 7.8 mg (1.2 mg and 3.9 mg) per day, respectively, and the intake in participants with a K6 score >13 was 7.4 mg (1.1 mg, and 3.5) mg per day, respectively.

However, BMI, medications for hypertension, hyperlipidaemia, diabetes, smoking, alcohol drinking, shift working, total energy and polyunsaturated fatty acids (PUFA) intake were not associated with depression and anxiety symptoms.

The lowest quartiles of zinc, copper, and manganese intake showed a statistically high age- and sex-adjusted OR compared to the highest quartiles. When smoking, alcohol drinking, BMI, work schedule, and intakes of folic acid, vitamin C, B6, B12, and PUFA were further adjusted for in Model 2, all associations between depression and anxiety symptoms and zinc, copper, and manganese intake remained statistically significant (zinc: OR, 1.91, 95% CI, 1.05–3.49). When further adjustments were made in Model 3 for medications for hypertension, hyperlipidaemia, and diabetes, OR for copper intake remained significant, but those for zinc and manganese intakes were slightly reduced and showed marginal significance (zinc: OR, 1.66, 95% CI, 0.89–3.09).

Furthermore, the trend analyses for the association between depression and anxiety symptoms and zinc, copper, and manganese intake were also statistically significant in all models. When the analyses were stratified by sex, the results were not substantially changed, although some results did not reach statistical significance, and the ORs were higher in women than in men in Model 1. After further adjustments, the multivariable-adjusted ORs of zinc and manganese intake tended to be lower than the age- and sex-adjusted ORs in men, and the multivariable-adjusted ORs for copper and manganese intakes tended to be higher than the age- and sex-adjusted ORs in women. When the analyses were stratified by age, the results did not change substantially, although the multivariable-adjusted OR for zinc intake showed an insignificant association with depression and anxiety symptoms in participants aged >40 years. The lowest quartiles of calcium, magnesium, and iron intake were not associated with mental disorders.

The intakes of the various minerals were broadly highly correlated among each other, with the exception of manganese intake. The combination analysis of high or low intake of zinc, copper, and manganese showed that low zinc and low copper intake, even with low or high manganese intake, had 3 times higher ORs for depression and anxiety symptoms compared to high zinc, high copper, and high manganese intake.

The results of this cross-sectional study in Japanese workers supported the inverse association between dietary zinc, copper, and manganese intake and depression and anxiety symptoms, independent of other dietary, lifestyle, and occupational factors, in the Japanese working population. The lowest quartiles of zinc, copper, and manganese intakes were associated with mental disorders. Furthermore, the simultaneous low intake of zinc and copper seemed to have an additive effect on this association.

This cross-sectional study revealed evidence that low intake of zinc, copper, and manganese were associated with mental disorders in Japanese workers. The study showed an association between zinc deficiency and mental disorders and supports the protective role of adequate zinc levels for mental health.

 

 

Epidemiological studies, RDT oral exposure - Meta-analysis
In this study, a systematic review and meta-analysis (Fernandez-Cao et al. 2019) was conducted to assess the association between dietary, supplementary, and total zinc intake, as well as serum/plasma and whole blood zinc concentration and the risk of Type 2 Diabetes mellitus (DM). The protocol for this systematic review and meta-analysis of observational studies was registered in PROSPERO (2015: CRD42015020178). The study was conducted in accordance with the Meta-Analyses of Observational Studies in Epidemiology (MOOSE) criteria statement.

From each manuscript selected for inclusion, the following data were extracted: study identification (first author’s name, year of publication, and name of the project), study characteristics (study design, period of follow-up, measure of association, adjustment variables, quality score, country, geographic regions, geographic area, sample base, matched design, sample size for each group and total, zinc assessment method, zinc quantiles adjusted for energy, ascertainment of T2DM, percentage of T2DM subjects, effect size, and 95% confidence interval (CI) for the most adjusted model), and study population (age, gender, ethnicity, area of residence—dietary, supplementary and total zinc intake, as well as serum, plasma, and whole blood zinc concentration—BMI, fasting glucose levels, stage of diabetes). To incorporate relevant data in forms other than the mean and standard deviation, such as median and the interquartile range, estimation methods were applied, which are valid for both normal and skewed data. When covariates of interest were expressed as a range, the midpoint of the range was assumed. If any of the data were missing, the authors were contacted for additional data. From 12 136 publications, 16 studies were selected. No association between supplementary or total zinc intake from both diet and supplementation and T2DM was observed. A direct relationship was found between serum/plasma zinc levels and T2DM. A moderately high dietary zinc intake, in relation to the Dietary Reference Intake (DRI), could reduce the risk of T2DM by 13%, and up to 41% in rural areas. Conversely, elevated serum/plasma zinc concentration was associated with an increased risk of T2DM by 64%, suggesting disturbances in zinc homeostasis.

Findings from this systematic review and meta-analysis revealed a potential protective effect of a moderately high dietary zinc intake, related to the DRI (adult men: 11 mg/day and women: 8 mg/day), on the risk of T2DM. These data seem to suggest that a dietary zinc intake within or slightly above the DRI could have a protective role on the risk of T2DM, but not when intake is very high. In addition, T2DM prevalence may be also a confounding factor for this association, being stronger when the prevalence is low, weak when it is moderate, and disappearing with a high prevalence. Conversely, no associations were observed between total or supplementary zinc intake and T2DM. In addition, an elevated serum/plasma zinc concentration was associated with an increased risk of T2DM in the general population. Meanwhile, high whole blood zinc concentration could be associated with T2DM, likely only at an early phase of the diabetes disease.

The results of this very comprehensive systemic review and meta-analysis support the evidence of protective effect of a moderately high dietary zinc intake on the risk of T2DM and an association between elevated serum/plasma zinc concentration and an increased risk of T2DM in the general population. The study supports that zinc plays an important role for the health of the general population and that supplementation of zinc needs to be balanced with respect to its protective role versus potential risks of high zinc intake.

 

 

Epidemiological studies, RDT oral exposure - Other human studies
A total 5 publications were identified to assess the effects of zinc deficiency and supplementation on the health status of children with asthma (Ghaffari et al. 2014), the associations between dietary/supplemental intakes of zinc (selenium and copper) and the risk for lung cancer (Mahabir et al. 2006), the association between the intake of six minerals (including zinc) and mental disorders (Nakamura et al. 2019), the relationship between low zinc concentrations with (non ) cardiovascular mortality (Pilz et al. 2008) and the effects of different amounts and sources of zinc on the frequency of diarrhoea, malaria, fever and respiratory tract infections (RTI) of children (Somé et al. 2015).

In a randomized, double-blind, placebo-controlled clinical trial (Ghaffari et al. 2014) conducted in patients of the public outpatient allergy clinic at Mazandaran University of Medical Sciences (Iran) it was shown that zinc supplementation at 50 mg/day in zinc deficient children (63 ± 8.6 μg/dL) with moderate asthma significantly improved both clinical symptoms and lung function in the case group (129 ± 20.4 μg/dL).

An ongoing case–control study (Mahabir et al. 2006) was assessed for the associations between dietary and supplemental intakes of zinc, selenium and copper, and the risk for lung cancer in patients from The University of Texas M. D. Anderson Cancer Center (Houston, USA) with lung cancer (cases) and healthy controls. The results indicated that when the dietary intakes of zinc, copper and selenium were analysed separately, increasing zinc (from <7.59 to >12.31 mg/d) and copper intakes were associated with lower risk of lung cancer, whereas selenium showed non-significant risk reductions only in the highest quartile of intake. Overall, increased dietary intake of zinc (and copper) was associated with a monotonically decreasing risk of lung cancer.

In a cross-sectional study (Nakamura et al. 2019), the association between the intake of six minerals (including zinc) and mental disorders was investigated among the Japanese working population. The results showed an inverse association between dietary zinc, copper, and manganese intake and depression and anxiety symptoms, independent of other dietary, lifestyle, and occupational factors, in this population. The lowest quartiles of zinc (7.4 mg/day), copper, and manganese intakes were associated with mental disorders (K6 score 13+). Furthermore, the simultaneous low intake of zinc and copper seemed to have an additive effect on this association.

A cohort study (Pilz et al. 2008) was designed to evaluate whether low zinc concentrations were associated with total, cardiovascular and non-cardiovascular mortality in patients referred to coronary angiography at the Heart Centre of the Ludwigshafen General Hospital, Southwest Germany. It was demonstrated that the risk for total, cardiovascular and non-cardiovascular mortality statistically significantly increased across the 4 serum zinc quartiles (<780 µg/l to >960 µg/l) with lowest cumulative survival in the first quartile. The hazard ratio for total and cardiovascular mortality remained highly significant even after adjustment for several possible confounders. The study data revealed that zinc deficiency was associated with total, cardiovascular and non-cardiovascular mortality.

In a community-based cluster randomised trial (Somé et al. 2015), the effects of different amounts and sources of zinc on the frequency of diarrhoea, malaria, fever and respiratory tract infections (RTI) in young children in rural southwestern Burkina Faso was assessed. However, in this trial, no evidence of an effects of different amounts and sources of zinc on these symptoms could be observed, although a large portion of the participants were diagnosed to be zinc deficient. The authors stated that it could not be ruled out that inadequate zinc absorption from SQ-LNS and insufficient adherence to the dispersible tablets were responsible for the absence of any detectable effect.

 

 

Human data - Epidemiological studies, RDT inhalation exposure
A human inhalation study with volunteers was performed to investigate on the systemic (Monsé, C. et al., 2018) and local (airway) (Monsé, C. et al., 2019) toxicity after exposition to self-synthesised zinc oxide nanoparticles. Sixteen young healthy subjects (eight males and eight females) were exposed to zinc oxide nanoparticles at concentration levels of 0 (sham), 0.5, 1.0, and 2.0 mg/m³ (analytical concentration) for four hours, with two weeks intervals for each subject. The subjects were generally at rest, excepts for four 30-minute intervals of moderate physical activity on a cycle ergometer. All examinations were conducted before the start (two to six weeks) of the exposure schedule (baseline test) as well as directly before (except for sputum parameters), immediately after, and 24 hours after each exposure. Moreover, a final test was performed two to six weeks after the last exposition to investigate on reversibility of potential effects. The subjects answered a questionnaire addressing flu-like symptoms, local airway effects (throat irritation and cough), and other question with regard to health status. Moreover, the body temperature, fractional exhaled nitric oxide, and lung function were examined. Blood was collected and analysed with regard to inflammation markers (blood cell counts, C-reactive protein (CRP), Serum amyloid A (SAA), Club cell protein (CC16), and IL-6) and coagulation (prothrombin F 1.2, endothelial microparticles, fibrinogen, and D-dimers). The zinc levels in blood and urine were monitored via ICP-MS. Moreover, induced sputum samples were obtained and analysed for inflammation biomarkers (IL-8, IL-6, and Substance P), oxidative stress markers (8-isoprostane (8-iso-PGF2α)), markers of structural remodelling (Tissue inhibitors of metalloproteinases (TIMP-1) and Matrix metalloproteinase (MMP-9)), and total protein level, as well as differential and total cell count.

Concentration-dependent increases in symptoms, body temperature, acute phase proteins, i.e. SAA and CRP, and neutrophils in blood were detected after zinc oxide inhalation. Significant effects were detected with zinc oxide concentrations of 1.0 mg/m³ or higher, with the most sensitive parameters being inflammatory markers in blood. Zinc oxide exposure had no effect on CC16, IL-6, and clotting factors in blood. The zinc level in blood and urine were unaffected by zinc oxide inhalation at any concentration tested. The questionnaire revealed flu-like symptoms at and above exposure to 1 mg/m³ zinc oxide. Moreover, there was a tendency for mild symptoms of airway irritation (throat irritation and cough) without showing a concentration-response relationship. The sputum parameters analysis revealed statistically significantly increased levels of MMP-9 (all concentrations), TIMP-1 (all concentrations), neutrophils (0.5 and 2.0 mg/m³), IL-8 (0.5 and 2.0 mg/m³), total protein (2.0 mg/m³), and IL-6 (1.0 and 2.0 mg/m³), when compared to the sham exposure values. However, the responses did not show concentration dependency. Moreover, effects on lung function parameters and FeNO were not observed. The final test showed full reversibility of the effects observed. Calculation of the deposition rates indicated tracheobronchial, inhalable, and alveolar deposition (combined) rates of 78%, 74%, and 66% as well as alveolar deposition of rates of 48%, 47%, and 44% estimated for the exposure to 0.5, 1.0, and 2.0 mg/m³, respectively. Based on the findings, the authors defined the NOEL for systemic inflammation to be between 0.5 and 1.0 mg/m³ based on pronounced effects on acute phase proteins and neutrophils. The NOEL for the reversible concentration-independent changes of parameters for inflammatory processes in the airways is considered to be below 0.5 mg/m³ based on the increase of inflammation biomarkers in sputum.

The human inhalation study with volunteers presented herein is generally reasonably well-described and conducted. However, the study showed some weaknesses. The parameters were recorded only at a low number of time points, and thus, some effects could have been missed due to maximum effects at other time points than recorded. Moreover, the study using the highest zinc oxide concentration levels (2.0 mg/m³) was not blinded, which could have potentially influenced the parameters recorded, especially with regard to the questionnaire, based on the nocebo-effect. Notably, four (25%) of the subjects did not indicate symptoms at any time point, some of the effects showed intra-individual inconsistencies, and most of the subjects (62.5%) indicated symptoms without zinc oxide exposure questioning the relevance of the findings presented. Especially the flu-like symptoms were similar comparing the pre- and post-sham exposure and the pre- and post-zinc oxide exposure group (2.0 mg/m³). Furthermore, most of the parameters assessed (e.g. biomarkers in blood and sputum) show large inter-individual variability and the relatively low sample size could have affected the results in both directions. In addition, reference values are for the most parameters assessed not available. Noteworthy, the systemic effects reported might have been affected by unadjusted environmental zinc exposure levels (e.g. zinc in diet). Moreover, the local effects did not show a concentration-response relationship, and thus, causality could not be demonstrated. The description of the exposure conditions lacks details.

In an ecological study using registry data (Lavigne et al. 2019), the long-term associations between metal components of particulate matter (PM) and mortality and lung cancer incidence were evaluated in a population in England. A land use regression (LUR) models was developed and used to predict PM10 and PM2.5 elemental composition for the study population. In the analyses, copper (Cu), iron (Fe) and zinc (Zn) in the PM10 fraction and copper and iron in the PM2.5 fraction were used, all linked to non-tailpipe emissions. Results showed statistically significant associations with PM metal concentrations for cardiovascular and respiratory mortality but not lung cancer incidence. Poisson regression suggested copper in the PM2.5 fraction had a statistically significant association with increased cardiovascular mortality risk, and PM10 zinc with respiratory mortality risk. However, metal exposures were highly correlated in this study and it is thus difficult to definitively attribute an association with one metal element.

Human data - Epidemiological studies, RDT dermal exposure
The safety of repeated application of agglomerated zinc oxide (ZnO) NPs applied to the skin of 5 healthy human volunteers (Mohammed et al. 2019) over 5 days at the University of Queensland, USA showed that repeated application of ZnO NPs, as used in global sunscreen products, appears to be safe, with no evidence of ZnO NP penetration into the viable epidermis nor toxicity in the underlying viable epidermis. It was associated with the release and penetration of zinc ions into the skin, but this did not appear to cause local toxicity.

 

 

Human data - Epidemiological studies, carcinogenicity
A study was conducted to determine the excess in lung cancer mortality associated with residence in an old-zinc mining and smelting area in the US (Neuberger et al. 1982). The age- and sex-adjusted mortality rates were compared to state and national rates. Age and sex specific lung cancer mortality rates were calculated for white individuals by county in Missouri (1968-1977) and Kansas (1973-1977) and then age adjusted. Additional lung cancer data were obtained from the Environmental Protection Agency (EPA) for Oklahoma, Kansas, and Missouri. Data were combined for the three counties to form one 'super-county.' The analysis determined that lung cancer mortality was elevated in the region. Quantification of inhabitant’s exposure to zinc was not part of the study. The authors mentioned several possible causes for the increased lung cancer rates such as smoking habits, occupational exposure (e.g. in mining and associated activities) and residence. Ore contaminants were arsenic, cadmium, iron, sulphur, germanium and radioactivity. Tuberculosis and silicosis were commonly seen among the region’s inhabitants. From this study any conclusion on a possible association between exposure to environmental levels of zinc and the increased lung cancer rate cannot be drawn.

A study was conducted to determine the relationship between supplemental zinc intake and prostate cancer risk among the participants in the Health Professionals Follow-Up Study (Leitzmann et al. 2003). The study was approved by the institutional review board on the use of human subjects in research of the Harvard School of Public Health. Follow-Up study was initiated in 51,529 male health professionals aged 40 to 75 years and follow-up questionnaires mailed biennially to cohort members to update information on newly diagnosed illnesses. Dietary intake was assessed with the use of a 131-item semi quantitative food-frequency questionnaire. Supplemental zinc provided 32% of total zinc intake representing the major source of zinc. Compared with nonusers, men who consumed supplemental zinc also consumed more multivitamins, supplemental calcium, supplemental vitamin E, lycopene, copper, iron, folate, and fish, but had lower intakes of red meat, and were slightly less likely to have had a history of prostate specific antigen screening. Non significant associations between supplemental zinc intakes at doses less than or equal to 100 mg/d and the risk of prostate cancer. However, compared with nonusers, men who consumed more than 100 mg/d of supplemental zinc had a relative risk of advanced prostate cancer of 2.29 (95% confidence interval = 1.06 to 4.95; Ptrend = .003), and men who took supplemental zinc for 10 or more years had a relative risk of 2.37 (95% confidence interval = 1.42 to 3.95; Ptrend <.001).Residual confounding by supplemental calcium intake or some unmeasured correlate of zinc supplement use cannot be ruled out, so the finding that chronic zinc oversupply may play a role in prostate carcinogenesis, warrant further investigation. Supplemental zinc intake at doses of up to 100 mg/d was not associated with prostate cancer risk. However, excessively high supplemental zinc intake may be associated with an increased risk of advanced prostate cancer.

A population based case-control study was conducted to examine association of dietary supplement use (including zinc) with prostate cancer risk in King County, Washington (Kristal et al. 1999). 697 incident prostate cancer cases (ages 40–64 yr) identified from the Puget Sound Surveillance, Epidemiology and End Results program registry and 666 controls recruited from the same overall population using random-digit dialing sampling. Participants reported their frequency of use of three types of multivitamins and single supplements of vitamins A, C, and E, calcium, iron, and zinc over the 2 yr before diagnosis. Logistic regression analyses controlled for age, race, education, family history of prostate cancer, body mass index, number of prostate-specific antigen tests in the previous 5 yr, and dietary fat intake. Although zinc use was rare, there was a borderline statistically significant 45 % reduction in risk of prostate cancer among those using zinc daily, with a significant test for trend. Adjusted odds ratios (95% confidence limits) for the contrast of ≥7/wk versus no use was 0.55. When cases were stratified by stage of disease at diagnosis, there was no suggestion of different effects among participants with early (stages A and B) and advanced (stages C and D) disease. When stratified by histopathological grade, somewhat stronger protective effect was observed in higher-grade disease, although trends were similar in both groups. The results of this study indicate that use of individual supplement of zinc may be protective against prostate cancer.

A population based case-control study was conducted to determine the association of dietary zinc level and brain tumour development (Dimitropoulouet al. 2008). The study was conducted between 2001 and 2004 in UK, comprising of adults aged 18–69 yr. Dietary information was collected from 637 cases diagnosed with a glioma or meningioma, and 876 controls. Data were obtained from a self-completed FFQ. Multivariate logistic regression analysis was conducted, adjusting for socio-demographic factors, season of questionnaire return, multivitamin supplementation and energy intake. Although a weak protective effect was observed for the third quartile of intake (normal compared with low intake) in the meningioma group, this was limited to the specific brain tumour subtype and quartile, and was not significant after also adjusting for intake of other elements. Overall there was no significant effect of zinc intake. In conclusion, no association or dose–response relationship was observed between increased vs. low zinc intake and risk of glioma or meningioma.

In a multicentre hospital based case-control study on prostate cancer, an association between high zinc intake and prostate cancer risk, particularly for advanced cancers was evaluated (Gallus et al. 2007). The study was conducted between 1991and 2002 in 1294 (cases) and 1451 (control). Zinc intake was computed from a valid and reproducible food frequency questionnaire, with the use of an Italian food composition database. Odds ratios (OR) of dietary intake of zinc and the corresponding 95% confidence intervals (CI) were estimated by unconditional multiple logistic regression models, after allowance for several covariates, including total energy. Compared with the lowest quintile, the OR for the highest quintile was 1.56 (95% CI, 1.07–2.26), with a significant trend in risk (p = 0.04). The trend in risk was significant for advanced cancers only, the OR being 2.02 (95% CI, 1.14–3.59) for prostate cancers with a high Gleason score. In this case-control study, a direct association between high zinc intake and prostate cancer risk, particularly for advanced cancers was observed and thus excluded the favorable effect of zinc on prostate carcinogenesis.

A cohort study was conducted on male workers exposed for at least one year in zinc refineries, to determine if the refinery operation is associated with any excess mortality patterns (Logue et al. 1982). Employees were incorporated in the study when they had worked in the electrolytic department for at least one year. Age-adjusted Standardized Mortality Ratio’s were calculated on the basis of comparison with the mortality rates for the entire population for the year 1970. Of the 1247 workers who were exposed to “zinc” (either alone or in combination with “copper”), 88 died before the end of the follow-up. For 12 of these, the cause of death could not be retrieved. 143 workers were lost to follow-up entirely. Cancer rates were only analysed for the entire cohort of refinery workers (i.e. all 4802 participants). Overall SMRs were calculated to be 92 for the cohort and 83 for the subgroup of zinc refinery workers. Significantly high cause-specific SMRs were as follows: (1) cerebrovascular disease (CBVD) for the cohort; (2) all cancers, cancer of the digestive tract, and CBVD for the copper subgroup; (3) all cancers, cancer of the respiratory tract, and CBVD for one plant that demonstrated a significantly high overall SMR. The significant excess of cancer deaths among the study cohort was largely due to the plant that exhibited the significantly high overall mortality rate, but lack of smoking data qualifies this finding. An association between cancer mortality and employment in zinc and/or copper refinery was not found, under the study conditions. A conclusion about any association between cancer mortality and zinc exposure cannot be drawn, because cancer mortality for “zinc”-workers was not analysed separately from cancer mortality for “copper”-workers.

A case-control study was conducted for analysing the association of prostatic cancer with the intake of particular nutrients, namely fat, vitamins A and C and zinc (Kolonel et al. 1988). A total of 452 cases of prostatic cancer, identified through the population based Hawaii Tumour Registry during the period 1977-1983, and 899 age-matched population controls were interviewed on the island of Oahu from 1981 to 1983. All interviews of the subjects, who comprised five different ethnic groups (Caucasian, Japanese, Chinese, Philipino, Hawaiian) were conducted in the home by use of a quantitative dietary history method. Usual weekly intake of fat, zinc, and vitamins A and C, including supplements, was determined for each subject. Among men 70 years or older, but not among younger men, the mean weekly consumption of saturated fat, carotenes, and zinc, adjusted for age and ethnicity, was greater for cases than for controls. In a multiple logistic regression analysis, the odds ratio for the highest quartile of fat intake among the older men was 1.7 (95% confidence interval (CL) 1.0-2.8). The corresponding odds ratios were 1.6 (95% CL1.0-2.5) for carotenes, 1.4 (95% CL 0.9-2.3) for total vitamin C, and 1.7 (95% CL 1.1-2.7) for total zinc. There were significant linear trends in the odds ratios for saturated fat and zinc, but no synergistic interactions among the nutrients. The results suggest that several different components of the diet may contribute independently to the risk of prostatic cancer in elderly men.

 

 

Epidemiological studies, oral exposure - Conclusion
Several publications support the evidence of the important role of a balanced zinc supplementation and homoeostasis for the health of patients and/or specific population groups.

It could be demonstrated that adequate zinc levels/intake were associated with a protective role on inflammatory markers (Jung et al. 2015) or the risk of chronic kidney disease (Kim et al. 2018) as well as the risk of atherosclerosis in Korean study populations (Yang et al. 2010), and was associated with a reduced risk of Crohn’s disease in woman in the USA (Ananthakrishnan et al. 2015). Zinc supplementation improved the clinical symptoms of children patients from the University of Medical Sciences in Iran with asthma and zinc deficiency (Ghaffari et al. 2014), and it was shown in a meta-analysis that dietary zinc intake within or slightly above the Dietary Reference Intake (DRI) could have a protective role on the risk of T2DM (Fernandez-Cao et al. 2019) However, elevated serum/plasma zinc concentrations were associated with an increased risk of T2DM. A protective effect of increasing levels of dietary zinc intake, in combination with copper (and selenium) on lung cancer could also be demonstrated in lung cancer patients from The University of Texas (Mahabir et al. 2006). In addition, it was shown in Japanese workers that low intake of zinc (copper, and manganese) was associated with mental disorders (Nakamura et al. 2019), and that in a specific group of patients referred to coronary angiography at the Ludwigshafen General Hospital, Germany (Pilz et al. 2008), zinc deficiency was found to be associated with total, cardiovascular and non-cardiovascular mortality. However, there was also evidence that different amounts and sources of zinc had no protective effect on the frequency of diarrhoea, malaria, fever and respiratory tract infections (RTI) in young children in Africa without or with zinc deficiency (Somé et al. 2015). Others showed no association between zinc intake from cow meat consumption and health risk in a Nigerian population (Ihedioha et al. 2014), or no consistent correlation between urinary zinc levels with several HRV parameters in China (Feng et al. 2015). An evaluation of serum zinc concentrations in the US population (Hennigar et al. 2018) showed that several factors may influence serum zinc levels including the time point of blood collection during the day, gender, haematological (haemoglobin) or clinical chemistry parameters (albumin) as well as anaemia and pregnancy in females.

With respect to dermal exposure it was demonstrated in human volunteers at the University of Queensland that repeated application of ZnO NPs, appears to be safe, with no evidence of ZnO NP penetration or toxicity in the viable epidermis (Mohammed et al. 2019).

Poisson regression analysis conducted in ecological study in England (Lavigne et al. 2019), suggested copper in the PM2.5 fraction had statistically significant association with increased cardiovascular mortality risk, and PM10 zinc with respiratory mortality risk. However, metal exposures were highly correlated in this study and it is thus difficult to definitively attribute an association with one metal element.

In the human studies described above, the effects of high or moderately high dietary zinc on several indicators known to be associated with copper status have been investigated. These indicators included plasma zinc and copper concentrations, cholesterol and lipoprotein cholesterol concentrations, and several enzyme activities (e.g. ESOD and ceruloplasmin). Effects of zinc on the latter are thought to precede changes in plasma and tissue levels of the elements, given the primary role of zinc as a component of different enzymes. In humans supplemented with zinc, plasma zinc concentration was elevated, while plasma copper concentration was not affected. In the earlier studies by Samman and Roberts (1987/1988), Yadrick et al., (1989) and Fischer et al. (1984) reductions in ESOD activity were found upon zinc supplementation. This was thought to be associated with copper deficiency, as was the reduction in ceruloplasmin activity found by Samman and Roberts (1987/1988). In the more recent and more sophisticated studies by Davis et al., (2000) and Milne et al., (2001), however, only very small reductions in ESOD activity were observed that did not correlate with changes in copper balance. The clinical significance of this ESOD reduction is questionable, because the findings in these studies on more specific copper deprivation signs (i.e., decreased serum ceruloplasmin and platelet cytochrome c oxidase) indicate that sub-optimal intake of zinc was more effective than a moderately high intake of zinc in inducing changes associated with a decreased copper status in postmenopausal women. It might also be that the small decrease in ESOD activity with high zinc intake was not caused by an interference with copper metabolism, but was more reflective of reduced oxidative stress given the serum glutathione and erythrocyte glutathione peroxidase findings. However, one can only conclude from the Grand Forks studies (Davis et al., 2000; Milne et al., 2001) that very subtle changes were induced by the different dietary treatments.

From various studies (e.g. Fischer et al., 1990; Barnett and King, 1995; Verhagen et al., 1996 and Puscas et al., 1999), it can be concluded that ESOD activities in healthy human volunteers may show a coefficient of variation of at least 10 to 20%. Although it is impossible to compare the absolute ESOD activities as reported by these authors to those from the Grand Forks studies, due to methodological differences, the relative changes in activities as reported by Davis et al., (2000) and Milne et al., (2001) can be compared to the coefficient of variation of ESOD activity, showing that the changes found in the Grand Forks studies are within the range of natural variation. In addition, Fischer et al., (1990) have demonstrated that in a large group of male and female human volunteers of different ages, ceruloplasmin and serum copper levels were highly correlated, but that no correlation between serum copper concentration and ESOD could be established. ESOD activity was independent of sex, age, pre/post-menopausal status, oestrogen use (including that in post-menopausal women), smoking or drinking habits, or level of physical exercise.

The general function of ESOD, also within red blood cells, is to catalyse the dismutation of superoxide anion radicals to hydrogen peroxide and oxygen, thus preventing damage of cell constituents and structures by this radical intermediate generated during the oxygen transport function. Concentrations of superoxide anion radicals are in the order of 0.01 – 0.001 nmol/l under non-pathological conditions. Hydrogen peroxide, on the other hand, is destroyed by catalase being present in high amounts within erythrocytes resulting in concentrations between 1 and 100 nmol/L. According to our knowledge there are only few measured data available showing a direct relationship between changes of intracellular concentrations of free radicals and tissue damage.

Assuming that there is a considerable reduction of the ESOD activity then higher concentration of superoxide radical anions should occur in red blood cells which may lead to destructive effects. Such effects should be detectable, e.g. by changes in haematological parameters (e.g., increased haemolysis, decreased number of erythrocytes, increase in reticulo¬cytes). However, such findings have not been observed in any study. In the Grand Forks studies (Milne et al., 2001) haematocrit, serum iron, and transferrin saturation were unaffected by a dose of 50 mg Zn/day leading to a 3-7% reduction of ESOD activity. Yadrick et al., (1989) reported a 47% decrease of ESOD activity after giving 50 mg Zn/day over 10 weeks However, this decrease of ESOD is accompanied by a small decrease in haematocrit value. The subtle changes in clinical-biochemical parameters, as reported in the Grand Forks studies, are hardly indicative for zinc-induced perturbations of the copper homeostasis. These biochemical changes do not lead to detectable deterioration of red blood cell functioning. Therefore, these changes are also of marginal biological significance, if any. Hence, it is concluded that in women supplemented with zinc, a dose of 50 mg Zn/day is the NOAEL.

From the newly evaluated data it can be concluded that lower zinc intake (below the RDI ~ <8 mg/day) or low serum zinc levels (<78 µg/dl) were associated with several risk including mental disorders, lung cancer, cardiovascular and non-cardiovascular mortality, subclinical atherosclerosis or chronic kidney disease. Intake of zinc was inversely associated with risk of CD; compared with individuals with intake of zinc less than the recommended daily allowance (8 mg/day), those with intake of 8–16 mg/day and >16 mg/day had a reduced risk of CD.

While supplementation with 50 mg/day was positively associated with the improvement of asthma symptoms in children, moderately high dietary zinc intake, in relation to the Dietary Reference Intake (11 mg/day for men; 8 mg/day for woman), could reduce the risk of T2DM. Higher serum zinc levels (89.9–119.9 μg/dL for men; 91.8–118.3 μg/dL for women) were shown to be partially responsible for lower acute inflammatory processes, particularly in woman.

However, it was also reported that higher zinc intake and elevated serum/plasma zinc concentrations were associated with an increased risk of T2DM (type II diabetes mellitus).

 

Epidemiological studies, inhalation exposure – Conclusion
The available data are limited, with merely one study in sixteen health volunteers is available. The studies investigate on the systemic (Monsé, C. et al., 2018) and local (airway) (Monsé, C. et al., 2019) toxicity after inhalation exposure towards self-synthesised zinc oxide nanoparticles at concentration levels of 0 (sham), 0.5, 1.0, and 2.0 mg/m³ (analytical concentration) for four hours, with two weeks intervals for each subject. The results of these studies are difficult to interpret, due to a number of methodological and reporting deficiencies as reported above. Consequently, the study is of little relevance for the hazard assessment of the zinc category.

 

Epidemiological studies, Effects on fertility/Developmental toxicity - Cross-sectional studies

The aim of this observational study (Bédard et al. 2018) was to investigate the associations between maternal intake of dietary antioxidants in pregnancy and childhood respiratory and atopic outcomes (including lung function). The ALSPAC is a population-based birth cohort that recruited 14 541 predominantly white pregnant female resident in Avon, UK with expected dates of delivery from April 1, 1991 to December 31, 1992. These pregnancies resulted in 13 613 singletons who were alive at 1 year of age. The cohort has been followed since birth with annual questionnaires and, since age 7 years, with objective measures in annual research clinics. Data on maternal diet in pregnancy were collected by a food frequency questionnaire (FFQ) sent out at 32 weeks gestation to mothers, covering all the main foods consumed in Britain. The questionnaire included questions about the weekly frequency of consumption of 43 food groups and food items. The FFQ was used to estimate daily nutrient intakes for each female, by multiplying the daily frequency of consumption of a food by the nutrient content of a standard portion of that food and summing this for all the foods consumed. Daily intakes of vitamins C and E, zinc, selenium, and carotene were estimated in this way. A maternal dietary antioxidant score was derived for each mother by adding the intake quartile for each of the five antioxidant nutrients, thus ranging from 5 to 20. Information on the child’s intake of antioxidants at 3 years, and maternal and paternal antioxidant intake at 4 years post-partum, was collected using a similar FFQ. Maternal smoking habits during the 3 months before pregnancy and at several time-points during pregnancy were recorded using self-reported questionnaires. For genotypes of interest, maternal DNA was a mixture of samples extracted from blood collected during pregnancy and from lymphoblastoid cell lines. The majority of the children’s DNA samples were extracted from cord blood or venous blood collected at age 7 years, with a small number extracted from venous blood collected at 43–61 months. The GSTT1 and GSTM1 gene deletion genotyping was performed using a real-time PCR. Two single nucleotide polymorphisms (SNPs) were typed in mothers and children by LGC Genomics (formerly KBiosciences, Hoddesdon, UK), using a competitive allele-specific PCR system (KASPar): a SNP in GSTP1 (G313A, Ile105Val, rs1695) and a SNP in GPX4 (glutathione peroxidase 4; rs713041, at position 718). Potential confounding factors that are known (from existing literature) to be associated with one or more of the outcomes of interest were selected: maternal age at delivery, sex of child, multiple pregnancy, season of birth, maternal history of atopic diseases (hay fever, asthma, eczema, allergies, or attacks of wheezing with whistling on the chest or attacks of breathlessness in the past 2 years), parity, highest educational qualification, housing tenure, financial difficulties, ethnicity, breast feeding duration and maternal factors during pregnancy (smoking status, anxiety score (Crown–Crisp Experiential Index), paracetamol use, antibiotic use, infections (urinary infection, influenza, rubella, thrush, genital herpes, other), supplement use and total energy intake (kJ·day−1)).
Of the 13 972 singletons and twins alive at 1 year of age, information on maternal diet during pregnancy was available for 12 078, of whom there was information on at least one of the outcomes of interest for 8 915 children. Maternal zinc intake during pregnancy in these population was 8.3 ± 2.4 mg/day. In this large, population-based, birth cohort study, it was demonstrated that a higher maternal zinc intake during pregnancy was associated, in a dose–response fashion, with higher FEV1 (forced expiratory volume in 1 s) and FVC (forced vital capacity) in the offspring, after controlling for potential confounders (difference in age-, height- and sex-adjusted SD units per quartile increase in maternal dietary zinc intake β 0.05 (95% CI 0.01–0.08); p=0.01 and 0.05 (95% CI 0.02–0.09); p=0.005, respectively). In addition, a weak evidence for an interaction between maternal zinc intake during pregnancy and maternal glutathione S-transferase (GSTM1) genotype on childhood FVC was found. The significant associations observed between maternal zinc intake and the maternal antioxidant score and childhood FEV1 and FVC also remained unattenuated after adjusting for child dietary zinc intake and antioxidant score, respectively, at age 3 years. Post hoc analyses of the associations between maternal zinc intake and childhood FEV1 and FVC at 15 years (n=3669) showed similar findings to those observed at 8 years. The graded nature of the associations between maternal zinc intake and lung function is in keeping with a causal effect on lung growth and development, and persistence of the association from childhood to adolescence strengthens causal inference further. While we also found positive associations between the maternal antioxidant score during pregnancy (derived from five antioxidant nutrients) and childhood lung function, these were largely explained by maternal zinc intake. A surprising observation was the lack of interaction between maternal intake of antioxidants and maternal smoking on childhood outcomes. No evidence to support a possible protective effect of maternal intake of vitamin E, zinc, fruits and vegetables during pregnancy on childhood asthma and atopy, nor were the other antioxidant nutrients associated with these outcomes. A plausible explanation for the associations observed between maternal zinc intake during pregnancy and childhood lung function, and especially FVC, was suggested to be that pre-natal zinc status influences growth and development of foetal lungs which is supported by the observation that zinc deficiency has been associated with impaired foetal lung growth in rats. The results of the study showed that a higher maternal intake of zinc during pregnancy may improve lung function, and especially FVC, in the offspring.
In total, 927 term newborns (503 males and 424 females) and their mothers were recruited. The median cord serum concentrations of Zn and Se were 794.3 µg/L and 63.1 µg/L, respectively. NBNA score was associated with maternal age, maternal education, paternal education, paternal occupation and household incomes. An independent relationship between Log10 (Lg)Zn or LgSe and NBNA scores adjusting for maternal age, gestational age, gender, maternal education, paternal education, maternal occupation, paternal occupation, and family incomes was shown. A non-linear relationship was observed between cord serum Zn or Se and NBNA score. NBNA score decreased with increasing Zn levels after the turning point (LgZn = 2.9, Zn = 794.3 µg/L). The threshold effect of LgZn on NBNA scores was significant after adjusting for potential confounders. Additionally, an invert U-shape with a threshold Se of 100 µg/L (LgSe = 2.0) was observed between cord serum Se and NBNA. The threshold effect of LgSe on NBNA scores was also significant after adjusting for potential confounders.
In this this epidemiological multi-centre study the effects of different levels of prenatal zinc (Zn) and selenium (Se) on foetal neurobehavioural development in neonates was investigated 927 mother-newborn pairs. A nonlinear relationship was observed between cord serum Zn and NBNA after adjusting for potential confounders. The results indicated that high level cord serum Zn had adverse effects on NBNA score, and both low and high levels of cord serum Se had adverse effects on NBNA score. A threshold effect of cord serum Zn and Se based on the neonatal neurodevelopment assessment was shown. The median level of cord serum Zn (794.3 µg/L) in the study was lower than the level reported in Arctic Canada (1097 µg/L) and similar to the level reported in Indian (727.7 µg/L). As to Se, the median cord serum Se level in our study (63.1 µg/L) was lower than Iran (124.80 µg/L) and similar to that reported in Baltimore in USA (69 µg/L). NBNA score decreased with increasing Zn levels after 794.3 µg/L. Additionally, an invert U-shape with a threshold Se of 100 µg/L was observed between cord serum Se and NBNA. High levels of both Zn and Se mainly had adverse effects on behaviour and passive tone (p< 0.001)
The study supports the evidence of an effect of serum cord Zn and Se levels on neurobehavioural development in neonates. High levels of both Zn and Se mainly adversely affected neonatal behaviour. However, dietary Zn and Se intakes in mothers were not investigated and the outcome of the study cannot be related to Zn alone, and need to be seen in the context with Se levels and may be also with other elements not investigated in the study.

In this this epidemiological multi-centre study (Yang et al. 2013) the effects of different levels of prenatal zinc (Zn) and selenium (Se) on foetal neuro-behavioural development in neonates was investigated. This multicentre study recruited 927 healthy pregnant women who came to the hospital to deliver a term (37–42 weeks of gestation) singleton infant in 10 maternity hospitals in Shanghai, China, from 2008 to 2009. Neonatal Behavioural Neurological Assessment (NBNA) was conducted when the infants were 3 days old. NBNA assesses functional abilities, most reflexes and responses, and stability of behavioural status during the examination. It contains five clusters: behaviour (six items), passive tone (four items), active tone (four items), primary reflexes (three items), and general assessment (three items). Each item has three levels (0, 1 and 2). Twenty items have a maximal total score of 40. Umbilical cord blood was collected and serum Zn and Se concentration were measured
In total, 927 term newborns (503 males and 424 females) and their mothers were recruited. The median cord serum concentrations of Zn and Se were 794.3 µg/L and 63.1 µg/L, respectively. NBNA score was associated with maternal age, maternal education, paternal education, paternal occupation and household incomes. An independent relationship between Log10 (Lg)Zn or LgSe and NBNA scores adjusting for maternal age, gestational age, gender, maternal education, paternal education, maternal occupation, paternal occupation, and family incomes was shown. A non-linear relationship was observed between cord serum Zn or Se and NBNA score. NBNA score decreased with increasing Zn levels after the turning point (LgZn = 2.9, Zn = 794.3 µg/L). The threshold effect of LgZn on NBNA scores was significant after adjusting for potential confounders. Additionally, an invert U-shape with a threshold Se of 100 µg/L (LgSe = 2.0) was observed between cord serum Se and NBNA. The threshold effect of LgSe on NBNA scores was also significant after adjusting for potential confounders.
In this this epidemiological multi-centre study the effects of different levels of prenatal zinc (Zn) and selenium (Se) on foetal neuro-behavioural development in neonates was investigated 927 mother-newborn pairs. A nonlinear relationship was observed between cord serum Zn and NBNA after adjusting for potential confounders. The results indicated that high level cord serum Zn had adverse effects on NBNA score, and both low and high levels of cord serum Se had adverse effects on NBNA score. A threshold effect of cord serum Zn and Se based on the neonatal neurodevelopment assessment was shown. The median level of cord serum Zn (794.3 µg/L) in the study was lower than the level reported in Arctic Canada (1097 µg/L) and similar to the level reported in Indian (727.7 µg/L). As to Se, the median cord serum Se level in our study (63.1 µg/L) was lower than Iran (124.80 µg/L) and similar to that reported in Baltimore in USA (69 µg/L). NBNA score decreased with increasing Zn levels after 794.3 µg/L. Additionally, an invert U-shape with a threshold Se of 100 µg/L was observed between cord serum Se and NBNA. High levels of both Zn and Se mainly had adverse effects on behaviour and passive tone (p< 0.001)
The study supports the evidence of an effect of serum cord Zn and Se levels on neuro-behavioural development in neonates. High levels of both Zn and Se mainly adversely affected neonatal behaviour. However, dietary Zn and Se intakes in mothers were not investigated and the outocome of the study cannot be related to Zn alone, and need to be seen in the context with Se levels and may be also with other elements not investigated in the study.

In this observational study (de Jong et al. 2002), the prevalence of anaemia and suboptimal iron and zinc status in pregnant women from three geographical regions (mountain, coast, city) of Zamboanga del Sur province was assessed. The study was carried out from October 1999 to May 2000 in three different geographical areas (city, mountain, coast) in the province of Zamboanga del Sur, the Philippines. The survey areas were selected on the basis of the 1995–97 health statistics of the province that indicated a high prevalence of premature births.
For phase I of the study, a total of 305 pregnant women at 24.1 ± 0.6 weeks of gestation (mean ± SD) were identified. Consenting women were included in the study if they were aged between 15 and 45 years, and if they had a normal, single pregnancy. Anthropometric, biochemical, general health and sociodemographic data were obtained at 24 weeks of gestation. Self-reported data were collected on prenatal dietary supplement use and pre-pregnancy weight. Health personnel registered birth outcome and also measured infant birthweight after delivery. For phase II of the study, a convenience sample of 127 women was selected from the initial sample of 305 women. A second nutritional assessment involving anthropometric, biochemical and clinical assessment was performed on this subsample at 36 weeks of gestation. Birth outcome and infant weight after delivery were also obtained in this subsample. Blood samples were collected from all women at 24 weeks of gestation and in a subsample of women at 36 weeks of gestation (n = 127). Haemoglobin analyses (cyanmethemoglobin method) and white blood cell count (WBCC) were performed. Serum ferritin was assayed, and the level of C-reactive protein as well as zinc in serum was measured. Hair samples were collected from the occipital portion of the scalp and analysed for zinc. Selected anthropometric measurements (height, weight, mid-upper arm circumference (MUAC), fundal height) were carried out in duplicate on the women at 24 weeks of gestation and on a subsample at 36 weeks of gestation, and self-reported pre-pregnancy weights were recorded. From delivery up to a maximum of 5 days after delivery, the birthweights of the infants were measured by the health personnel in charge. A general questionnaire, containing questions on age, sociodemographic variables, use of vitamin and mineral supplements and medications, medical and obstetrical history and, for the subsample, type of diet (i.e., maize or rice as a staple food) was completed by each woman.
With respect to the biochemical iron indices and serum zinc results at 24 weeks of gestation, no relevant differences existed among the three geographical areas nor between the rice versus maize eaters. The prevalence of biochemical parameters below specific cut-off levels was not significantly different among the three areas either. Of the total group, 34% had serum ferritin concentrations less than 12 μg/L, with or without anaemia. Likewise, in the whole group, the prevalence of anaemia was also 34% (with or without low serum ferritin values), based on a cut-off value for haemoglobin specific for the second trimester (i.e., <105 g/L). However, when the non-gestational appropriate WHO cut-off value of 110 g/L was applied, 51% of the women were classified as anaemic. Haemoglobin and serum zinc were significantly correlated at 24 weeks (p<0.001; n = 271), but not at 36 weeks of gestation (p<0.21; n = 84). No significant gestational age-related differences were observed for serum zinc concentrations. The mean birthweight in the total group (phase I) was 3074 ± 408 g (n = 250). The prevalence of low birthweight (i.e., <2500 g) was 5% in the total group. There were no statistically significant differences in birthweight among the three different areas, nor between the maize and rice eaters. No significant associations between maternal weight gain and infant birthweight (P > 0.28), or between (changes in) biochemical iron and zinc parameters and infant birthweight (P > 0.16) were apparent. However, a statistically significant difference (P = 0.05) in birthweight (3003 g vs 3114 g) was observed when women were classified as anaemic versus non-anaemic (cut-off point of 105 g/L). Women with serum zinc values below 7.1 μmol/L tended to have infants with a lower birthweight (2965 g) compared to women with serum zinc values above the cut-off (3077 g), but this trend was not significant (P = 0.14). Serum zinc at 24 weeks approached significance (P = 0.07).
In this study, the prevalence of anaemia and suboptimal iron and zinc status in pregnant women from three geographical regions (mountain, coast, city) of Zamboanga del Sur province at 24 weeks and again at 36 weeks of gestation were assessed. No differences existed for biochemical indices or birthweight among the three regions, or between women consuming maize or rice-based diets. Women with low haemoglobin (P = 0.05) and low serum zinc (P = 0.14) values at 24 weeks gestation had infants with lower birthweights than those with values ≥ 105 g/L and ≥ 7.1 μmol/L, respectively.
The results of this study support the evidence that lower maternal zinc status during pregnancy is associated with lower birth weight of infants. However, in this study the correlation was not significant.

Samples from the ongoing Navajo Birth Cohort Study (NBCS) in pregnant woman were chosen to investigate the association between environmental metal exposure (to uranium mine waste affects) and oxidative stress biomarkers, and to determine whether serum zinc moderates the effects of these exposures (Dashner-Titus et al. 2019).

Materials and Methods: In 2013, recruitment of pregnant women for the NBCS study between 14 and 45 years of age who had lived on the Navajo Nation for at least 5 years begun, who were willing to deliver at a participating hospital, and have their child followed up for one year postnatally. At the time of enrolment, a blood and urine sample was collected from the participant. Socioeconomic, demographic, and lifestyle information was also collected in the home shortly after enrolment. A subset of the maternal enrolment urine samples was selected for oxidative stress analysis, which forms the basis of this investigation. For the present study, urine samples from participants were stratified by serum zinc concentration above and below the WHO level of sufficiency of 70 μg/dL.

The sample population was limited to individuals who also had their enrolment urine sample analyzed for uranium, total arsenic, arsenous (III) acid (arsenite, AsIII), and dimethylarsinic acid (DMA). Then 66 urine samples from each zinc group were randomly selected for inclusion in the present study out of 204 women enrolled in the trial at that time.

Urinary total arsenic, AsIII, DMA, uranium and serum zinc, were measured by ICP-DRC-MS. Oxidative stress biomarkers as measured by HPLC-Tandem Mass Spectrometry included 8-iso-PGF2α as a well-regarded marker for detection of chemical lipid peroxidation. PGF2α was also detected and the and the prostaglandin ratio calculated.

Results: All 132 participants included in this study were pregnant women between the ages of 16 to 42 with a median age of 26.8 years old. Analysis of survey information indicated that 38.6% of women had education beyond high school, 57.6% were unemployed and 43.2% had an annual household income below $20,000 at the time of study enrolment. The majority of women (59.8%) were taking vitamin supplements and were overweight or obese based on pre-pregnancy BMI (52.2%). Current cigarette smoking is negligible among the pregnant women (<1%) which is consistent with low tobacco usage overall in the Navajo population. However, other exposures such as wood or coal heating or use of ceremonial tobacco were noted as potential contributors to oxidative stress.

Of the 132 individuals in the sample population, urinary metals were detected among 132 (100%) for urinary total arsenic, 105 (79.5%) for urinary DMA, 88 (66.7%) for urinary AsIII, and 128 for urinary uranium (97.0%). Serum zinc was detected in all 132 (100%) individuals from the sample population. The median concentration for serum zinc was 67 μg/dL and median concentrations for urinary total arsenic, DMA, AsIII, and uranium were 5.5 μg/g, 4.3 μg/g, 0.41 μg/g, and 0.016 μg/g creatinine respectively. Serum concentrations of zinc were lower in NBCS participants when compared to National Health and Nutrition Examination Survey (NHANES) (p-value<0.001).

Concentrations of urinary AsIII and serum zinc decreased from the 1st to 3rd trimester while concentrations of urinary uranium, total arsenic, and DMA remained stable. No significant difference in urinary uranium or arsenic concentrations between the low versus high zinc groups were observed suggesting that zinc status did not influence urinary metal levels. The median concentration for the high zinc group was 78 μg/dL, which is similar to the NHANES values of 80 μg/dL and above the WHO sufficiency standard of 70 μg/dL. The median for the low zinc group was 48 μg/dL and well below the NHANES values and zinc sufficiency standard. The high and low zinc groups did not differ in the demographic characteristics with the exception of smoker classification. There were more Never Smokers and fewer Former Smokers in the low zinc group. Additionally, the high zinc group included more women who enrolled in the NBCS during the 1st trimester and low zinc group had more women enrol during the 3rd trimester.

Of the oxidative stress biomarkers measured in this study, PGF2α and the prostaglandin ratio, but not 8-iso-PGF2α, were significantly different based on pregnancy trimester. When only zinc is considered, comparison between the low and high zinc status subsets revealed no difference in the oxidative stress biomarkers 8-iso-PGF2α or the prostaglandin ratio. In a univariable analysis of the linear regression model there were no significant associations with environmental metals and 8-iso-PGF2α. A multivariable analysis revealed significant main effects and interaction effects between total arsenic and low zinc on the 8-iso-PGF2α outcome. It was observed that the association between total arsenic and oxidative stress was modified by zinc group. Specifically, arsenic was positively associated with increased 8-iso-PGF2α for the high serum zinc group, but not for the low serum zinc group. In terms of the mediation effect of zinc on the association or metal/metalloids with oxidative stress, the causal mediation analysis yielded no significant results of zinc mediation.

Summary: It was hypothesized for this cohort study (NBCS) in pregnant woman that the zinc status would have an impact on metal-associated oxidative stress based on the antioxidant properties of zinc. However, no definitive evidence that zinc mediated the arsenic effect with regard to the oxidative stress biomarker 8-iso-PGF2α was obtained. Despite established antioxidant properties of zinc, zinc was not found to have causal mediation of the effects of the other metals on oxidative stress.

Evaluation and Reliability: The results of this cohort study in pregnant woman are not useful in a regulatory context. An effect of the antioxidant properties of zinc on metal-associated oxidative stress could not be demonstrated.

 

 

Epidemiological studies, Effects on fertility/Developmental toxicity - Controlled clinical trial

This study of Caulfield et al. 2010 represents a double-blind, randomized, controlled clinical trial in children which received prenatal zinc supplementation via their mothers. A double-blind, randomized, controlled trial of prenatal zinc supplementation was conducted among women receiving prenatal care at Centro Materno Infantil San Jose, in Villa El Salvador, Lima, Peru. When the children were approaching 54 mo of age, they were located to evaluate their health, nutritional status, developmental outcomes and autonomic functioning. 242 women were enrolled in the study at 10–14 wk of gestation and were randomized within strata (based on week of gestation and parity) to receive daily supplements containing 60 mg iron (as ferrous sulfate) and 250 mg folic acid, with or without an additional 25 mg zinc (as zinc sulfate).
Of the 242 women enrolled in the trial, 222 (90.1%) completed the protocol and 195 (80.6%) were included in the formal analysis, 94 in the zinc group and 101 in the control group (19). For those analyses, the data from 27 mother-infant pairs with obstetrical or medical complications were excluded, but for the follow-up study an attempt was made to locate 10 of these mothers who had completed the protocol and whose babies survived the neonatal period and were free of congenital malformations. From this pool of 205 eligible participants, evaluations were conducted for 184 (90%) children, 86 whose mothers had received zinc supplements during pregnancy, and 98 whose mothers had not. When the children reached 54 mo of age, the study physician conducted a physical exam, which included an assessment of their diet and nutritional status. From this examination, the mean arterial pressure as [diastolic pressure + (systolic pressure 2 diastolic pressure)/3] was calculated, and body size in terms of both BMI [weight (kg)/height (m2)] as well as body surface area [BSA = 0.024265(height in cm0.3964) (weight in kg0.5378)] was characterized, the latter being more related to cardiac function measures. Each child’s haemoglobin concentration and plasma zinc concentration as a measure of zinc status were measured. Haemoglobin concentration is available for almost all children, but information on plasma zinc concentration only for a subset of 115 children (those with earlier birth dates). Relevant history on postnatal morbidity, infant feeding, growth, and development were also recorded based on maternal report and abstraction from clinic records. Over 2 sessions, child heart rate (HR) data were derived telemetrically using 2 paediatric electrodes embedded in a belt secured on the child’s chest under a shirt. R-waves were collected, amplified, and timed by a commercially available apparatus (Mini-Logger 2000, Mini Mitter). Five minutes of electrocardiogram (ECG) data were collected with the child sitting quietly to characterize baseline values immediately followed by a series of tasks designed to evaluate child developmental outcomes. Five cardiac measures were derived to reflect the spectrum of current analysis methods: 1) heart period (HP), the intervals between R-waves (ms); 2) range of HP; 3) HP variability (HPV), SD of HP within epochs (i.e. time-independent variability); 4) mean square of successive differences (MSSD), a time-dependent method of analysing variation in successive HP; and 5) vagal tone (V). Following the baseline record, child developmental outcome was assessed using the Spanish adaptation of a standard intelligence test (Wechsler Preschool and Primary Scale of Intelligence) and a comprehensive protocol for studying multiple facets of cognitive and behavioural functioning developed at the Child and Family Research Section of the U.S. Eunice Kennedy Shriver National Institute of Child Health and Human Development and adapted for this age group of Latin American children.
At follow-up, most children were characterized by their mother as healthy overall, but almost 30% in each group had a cold on the first day of testing. There were no differences in child weight, height, BMI, BSA, or anaemia between groups. Using the cut-off point of 9.9 mmol/L for zinc deficiency there were no differences between the zinc (21.8%) and control (13.3%) groups (p=0.23). The only difference between groups noted was a somewhat lower mean diastolic blood pressure among children whose mothers received supplemental zinc during pregnancy (P<0.10). Children whose mothers consumed supplemental zinc (along with iron and folic acid) had greater HP (that is, slower HR), greater range, and more variability in HP as assessed by either the time-independent method (HPV) or the time-dependent one (MSSD), and higher V compared with children of women in the iron and folic acid only supplement group (P<0.05). Correlations across the 10 measurement periods (baseline and 9 cognitive segments) for each of the 4 HR variables ranged from 0.43 to 0.94 (P<0.05), indicating moderate to high degrees of stability for cardiac measures for individual children over time. Results indicate that children in the maternal zinc supplementation group continued to have longer HP (slower HR) and higher time independent and -dependent indicators of variability (HPV and MSSD) during challenge afforded by testing. The differences in V and range neared significance (P = 0.08). There were no treatment group differences in plasma zinc concentration at follow-up. However, plasma zinc concentrations were significantly and positively associated with HP (r = 0.210) and range (0.209) and tended to be associated with MSSD (0.167; P= 0.07). Adjustment for concurrent plasma zinc concentration did not alter conclusions regarding supplement type differences in the cardiac measures during baseline.
In this study, consistent effects of prenatal zinc supplementation on measures of autonomic functioning indexed by cardiac patterns in early childhood were found. Detected differences in HR and its patterning were evident both during an undisturbed baseline period as well as during an extended period of challenge afforded by a battery of complex developmental tests. The results support the interpretation that inadequate maternal intake of zinc during pregnancy alters the development of autonomic regulation in the developing foetus, which reach into childhood. In addition, prenatal zinc supplementation influenced parasympathetic control during cognitive testing, suggesting that zinc sufficiency during the most intensive period of autonomic nervous system development exerts long-term influences on parasympathetic control during cognitive challenge.
The results of this double-blind, randomized, controlled clinical trial in children which received prenatal zinc supplementation via their mothers supports the evidence of a positive effect of prenatal zinc supplementation on the development autonomic nervous system in utero.

 

 

Epidemiological studies, Effects on fertility/Developmental toxicity - Meta analysis

In this publication Liu et al. 2018, the effects of zinc supplementation on child growth was systematically reviewed and meta-analysed from randomised controlled trials. To evaluate the effects of preventive zinc supplementation for 3 months or longer during pregnancy or in children up to age 5 years on pregnancy outcomes and child growth, a literature search was conducted in PubMed, EMBASE, Cochrane Library, Web of Science, and trial registries for eligible trials up to October 10, 2017. Findings were pooled using random effects meta-analysis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, with heterogeneity assessed by I2 and τ2 statistic, stratified analyses, and meta-regression, and publication bias by Egger’s and Begg’s tests.

The exposure of interest was zinc supplementation during pregnancy, in infants (up to 24 months), or in children (up to 5 years). For endpoints measured at birth, the growth outcomes of interest were birth weight and low birth weight (LBW, defined as birth weight < 2500 g). For outcomes measured in children, the growth outcomes of interest were height, weight, corresponding Z-scores including height-for-age (HAZ), weight-for-age (WAZ), and weight-for-height (WHZ), and the risk of stunting wasting, and underweight. Seventy-eight trials with 34 352 unique participants were identified, including 13 167pregnant mothers (24 trials) and 20 412 infants <2 years old (47 trials), and 773 children aged 2 years or older (7 trials) who received supplementation. The results showed that maternal zinc supplementation did not significantly increase birth weight or decrease the risk of low birth weight. Zinc supplementation after birth increased height, weight, and weight-for-age Z-score, but not height-for-age Z-score or weight-for-height Z score. Child age at zinc supplementation appeared to modify the effects on height (P=0.002) and HAZ (P=0.06), with larger effects of supplementation starting at age >2 years. No significant effects of supplementation were found on the risk of stunting, underweight or wasting.
The current meta-analysis indicates that zinc supplementation in infants and during early childhood, but not pregnancy, increases specific growth outcomes including height, weight, and WAZ, with evidence for a potentially stronger effect after 2 years of age. The findings support a role of zinc for certain child growth outcomes in infants and children under five years of age. The identified modest effect size may not justify universal zinc supplementation. However, larger effects may be observable among children with sub-optimal zinc status.
This systematic review and meta-analysis on the effects of zinc supplementation in general supports the evidence of a positive effect of zinc supplementation in young children but not during pregnancy.

 

Epidemiological studies, Effects on fertility/Developmental toxicity - Conclusion

Effects on Fertility, Human information
In reviews by the World Health Organisation in the Environmental Health Criteria for Zinc (WHO, 2001) and by the US Agency for Toxic Substances and Disease Registry in the Toxicity Profile for Zinc (ATSDR, 2005), existing human studies which examined the responses of women to zinc supplementation during pregnancy have been summarised. Studies on large controlled trials that were conducted to investigate the effects of dietary zinc supplementation in healthy pregnant women were peer reviewed. The reviewers concluded that zinc at a rate of 20mg/day and 30 mg/day did not result in any adverse reproductive effects during pregnancy (Hunt et al., 1984; Kynast and Saling et al., 1986). Two exemplar studies are summarised in the following:
A double blind trial was conducted in 56 pregnant women at risk of delivering a small for gestational-age baby to determine the effects of dietary zinc supplementation during the last 15-25 weeks of pregnancy following administration of 22.5 mg zinc/day. No adverse reproductive effects were observed (Simmer et al., 1991).
Pregnant women who received 0.3 mg zinc/kgbw/day as zinc sulphate capsules during the last two trimesters did not exhibit any changes in maternal body weight gain, blood pressure, postpartum haemorrhage or infection, inidicating no adverse reproductive effects (Mahomed et al., 1989).

 

Developmental toxicity, Human information
In establishing the Environmental Health Criteria for Zinc, the World Health Organisation has reviewed and summarised existing human studies examining the responses of women to zinc supplementation during pregnancy. None of the studies indicated any significant effects on the developing foetus (WHO, 2001). Two exemplar studies are summarised in the following:
A study was conducted on pregnant women to determine the effects of nutrients during pregnancy on maternal and foetal outcome. Four hundred fifty women were observed during pregnancy and postpartum. Forty-three variables including 12 laboratory indices of maternal nutrient status were assessed. Maternal plasma zinc levels were inversely correlated with foetal weight. Blood examinations revealed a significant association between the total occurrence of fetomaternal complications or foetal distress, and lowest quartile zinc/albumin and highest quartile folate. Under the study conditions, plasma zinc was determined to be a discriminator for fetomaternal complications only in women in the lowest quartile for plasma zinc (Mukherjee et al., 1984).
A double blind trial was conducted on pregnant women to determine the effects zinc supplementation during pregnancy on maternal and foetal outcome. 494 women booking before 20 week of gestation in a hospital were prescribed either 66 mg zinc sulphate (equivalent to 20 mg elemental zinc, 0.3 mg zinc/kgbw/day) capsules or placebo for once daily use, starting from day of booking till delivery. Various adverse outcomes were tested, including maternal bleeding, hypertension, complications of labour and delivery, gestational age, Apgar scores, and neonatal abnormalities. The main outcome measure was birth weight. There were no differences between the mothers and neonates of the zinc supplemented and placebo group. Under the test conditions, zinc supplementation during pregnancy did not affect maternal or foetal outcome (Mahomed et al., 1989).
In summary, in studies with women receiving zinc supplementation during pregnancies at levels of approximately ≤ 0.3 mg Zn/kg bw/day, no reproductive or developmental effects were observed (WHO, 2001; SCF, 2003). Evidence of zinc toxicity during human pregnancy has not been reported, but this may be due to the fact that very high exposures to zinc in human pregnancy are unusual. In contrast, zinc is necessary for normal growth and development (e. g., gene expression, vitamin metabolism) and therefore it is not surprising that zinc deficiency during pregnancy can cause a variety of adverse effects to the foetus or may result in reduced fertility or delayed sexual maturation in animals as well as in humans (EU RAR, 2004; WHO, 2001).

In 3 human studies with zinc supplementation, the evidence of a positive effect of prenatal Zn supplementation was supported in 2 studies (Bédard et al. 2018, Caulfield et al. 2010), or postnatal zinc supplementation in the third study (Liu et al. 2018). In a cohort study (Dashner-Titus et al. 2019), it could not be demonstrated that different serum zinc levels of mothers hat an effect on oxidative stress biomarkers. The effect of high level of prenatal Zn and Se on foetal neurobehavioural development in neonates was investigated as well (Yang et al. 2013). An association between lower maternal zinc status during pregnancy and lower birth weight of infants could be demonstrated (de Jong et al. 2002).
In an observational cohort study (Bédard et al. 2018), the associations between maternal intake of dietary antioxidants in pregnancy and childhood respiratory and atopic outcomes (including lung function) was investigated. It was demonstrated that a higher maternal zinc intake during pregnancy (8.3 ± 2.4 mg/day) was associated, in a dose–response fashion, with increased lung functions as shown by a higher FEV1 (forced expiratory volume in 1 s) and FVC (forced vital capacity).
A double-blind, randomized, controlled trial (Caulfield et al. 2010) with prenatal daily supplementation by 60 mg iron (as ferrous sulfate) and 250 mg folic acid, with or without an additional 25 mg zinc (as zinc sulfate) was conducted among women and their children to assess the effects on autonomic functions in children at an age of about 54 months. The results indicated a consistent effects of prenatal zinc supplementation on measures of autonomic functioning indexed by cardiac patterns in early childhood. The results support the interpretation that inadequate maternal intake of zinc during pregnancy alters the development of autonomic regulation in the developing foetus, with reach into childhood.
The effects of zinc supplementation on child growth was systematically reviewed from randomised controlled trials by Liu et al. (2018) and a meta-analysis was conducted. The results indicated that zinc supplementation in infants and during early childhood, but not pregnancy, increases specific growth outcomes including height, weight and weight-for-age, with evidence for a potentially stronger effect after 2 years of age.
Another birth cohort study in pregnant woman (Dashner-Titus et al. 2019) was conducted to investigate the association between environmental metal exposure (to uranium mine waste affects) and oxidative stress biomarkers, and to determine whether serum zinc (median concentration of serum zinc was 67 μg/dL) moderates the effects of these exposures. Despite established antioxidant properties of zinc, zinc was not found to have causal mediation of the effects of the other metals on oxidative stress under the conditions of this study
In an epidemiological study (Yang et al. 2013), the effects of different levels of prenatal zinc (Zn) and selenium (Se) on foetal neurobehavioural development in neonates was investigated. The results indicated that a high level of cord serum Zn as well as both low and high levels of cord serum Se had adverse effects on neonatal behavioural neurological assessment (NBNA) scores. The NBNA score decreased with increasing Zn levels after 794.3 mg/L.
In an observational study (de Jong et al. 2002), the prevalence of anaemia and suboptimal iron and zinc status in pregnant women from three geographical regions (mountain, coast, city) of Zamboanga del Sur province at 24 weeks and again at 36 weeks of gestation were assessed. The results indicated that women with low haemoglobin (P = 0.05) and low serum zinc (P = 0.14) values at 24 weeks gestation had infants with lower birthweights than those with values ≥ 105 g/L and ≥ 7.1 μmol/L, respectively.

In the IUCLID endpoint summary (2014) it is stated that in studies with women receiving zinc supplementation during pregnancies at levels of approximately ≤ 0.3 mg Zn/kg bw/day, no reproductive or developmental effects were observed (WHO, 2001; SCF, 2003). In contrast, zinc is necessary for normal growth and development (e.g., gene expression, vitamin metabolism) and therefore it is not surprising that zinc deficiency during pregnancy can cause a variety of adverse effects to the foetus or may result in reduced fertility or delayed sexual maturation in animals as well as in humans (EU RAR, 2004; WHO, 2001).
The newly evaluated data from human epidemiological and cohort studies support the evidence of a positive effect of prenatal and postnatal zinc supplementation on the development of offspring in most publications. However, there might be a threshold of the occurrence of adverse effects in neonates at a certain level of zinc concentrations in the blood of their mothers.

 

 

 

 

 

 

 

 

Human data considered not relevant
Shakoori et al. 2016. Successful management of zinc phosphide poisoning. Indian J Crit Care Med. 2016 Jun; 20(6): 368–370.
- description of a case of massive Zn2P3 poisoning in an 18-year old male related to the formation of PH3 in the luminal tract and not related to zinc - not relevant.

Gellein et al. 2003. Concentrations of Cd, Co, Cu, Fe, Mn, Rb, V, and Zn in Formalin-Fixed Brain Tissue in Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex of Guam Determined by High-Resolution ICP-MS. Biological Trace Element Research. Vol. 96.
– Measurement of different essential and toxic metals including Zn in the brain of amyotrophic lateral sclerosis (ALS) and parkinsonism–dementia complex (PDC) patients – not relevant.

AbdulWahab et al. 2015. Serum zinc concentration in cystic fibrosis patients with CFTR I1234V mutation associated with pancreatic sufficiency. The Clinical Respiratory Journal.
– Mean plasma Zn levels in cystic fibrosis patients belonging to the same Arab tribe – not relevant.

Alipour et al. 2011. Relationship between serum zinc, iron and copper level and apoptosis in human gastric mucosa: A cross-sectional study. Pakistan Journal of Nutrition 10 (10): 919-924.
– No relationship was identified between serum zinc, iron and copper levels and apoptosis (as an early indicator of gastric cancer changes) in human gastric mucosa – not relevant.

Arinola et al. 2018. Household air pollution, levels of micronutrients and heavy metals in cord and maternal blood, and pregnancy outcomes. Int. J. Environ. Res. Public Health 2018, 15, 2891.
- Smoke from kerosene stove was associated with reduced birth weight and micronutrients imbalance in mothers and newborns – not relevant.

Bortey-Sam et al. 2018. Association between human exposure to heavy metals-metalloid and occurrences of respiratory diseases, lipid peroxidation and DNA damage in Kumasi, Ghana.
- Urinary metal/metalloid concentrations were studied in Kumasi residents, and although Zn was most abundant, urinary As was higher in 83% of participants compared to recommended levels – no useful information.

Fluegge 2017. Zinc and Copper Metabolism and Risk of Autism: a reply to Sayehmiri et al. Iran J Child Neurol. SUMMER 2017 Vol 11 No 3.
- Reply to a meta-analysis conducted to explore the relationship between zinc and copper metabolism and autism spectrum disorders (ASD). It is argued that gestational exposures to air pollutants are causative and that the described nutritional phenotypes may be a purposeful compensatory mechanism (and not just a consequence) to counter air pollutant exposures – not relevant

Gutiérrez-Gonzalez et al. 2018. Dietary zinc and risk of prostate cancer in Spain MCC-Spain study. Nutrients 2019;11(18).
- Epidemiological study in a very specific study population of patients with prostate cancer and the association between zinc intake and tumor aggressiveness and extension, as well as genetic susceptibility – not relevant

Herlin et al. 2019. Exploring telomere length in mother-newborn pairs in relation to exposure to multiple toxic metals and potential modifying effects by nutritional factors. BMC Medicine (2019) 17:77.
-Multiple toxic metals were measure in the maternal blood or urine collected during late pregnancy, as well as the placenta and cord blood collected at delivery in a mother–child cohort in northern Argentina. No association was found for zinc. – not relevant

Khabour et al. 2018. Plasma and saliva levels of three metals in waterpipe smokers a case control study. Inhal Toxicol. 2018 May; 30(6): 224–228.
- Waterpipe tobacco smoking is associated with elevated levels of metals (including zinc) in plasma and saliva. – not relevant

Kindgren et al. 2019. Heavy metals in fish and its association with autoimmunity in the development of juvenile idiopathic arthritis A prospective birth cohort study. Pediatric Rheumatology (2019). 17:33.
- The possible influence of early nutrition on later development of Juvenile Idiopathic Arthritis (JIA) was evaluated. Moderate exposure to heavy metals (Al, Cd, Hg and Li but not Zn in cord blood), associated with fish consumption, during pregnancy and early childhood may cause effects on the immune system of the offspring. – not relevant

Long et al. 2019. Zinc Absorption from Micronutrient Powders Is Low in Bangladeshi Toddlers at Risk of Environmental Enteric Dysfunction and May Increase Dietary Zinc Requirements. The Journal of Nutrition, Nutrient Requirements and Optimal Nutrition. January 9, 2019.
- Results of the clinical trial indicate impaired absorption of zinc, which may predispose to zinc deficiency in young children with evidence of enteropathy. – not relevant

Mahmoud et al. 2016. Zinc intake and risk of prostate cancer Case-control study and meta-analysis. PLOS ONE. November 8, 2016.
- The association between self-reported zinc intake and prostate cancer in a hospital-based case-control study of African Americans was investigated and the results compared with previous studies by meta-analysis to summarize the evidence regarding the association between zinc and prostate cancer - no evidence for an association between zinc intake and prostate cancer was found – not relevant

Park et al. 2013. Serum zinc and prostate cancer risk in a nested case-control study: the Multiethnic Cohort. Prostate. 2013 February 15; 73(3): 261–266.
- case-control study nested within the Multiethnic Cohort of African Americans, Native Hawaiians, Japanese Americans, Latinos, and whites in Hawaii and California to evaluate the association between prediagnostic serum zinc and prostate cancer risk - no evidence to support an inverse relationship between serum zinc and prostate cancer risk was found – not relevant

Martin-Moreno et al. 2003. Myocardial infarction risk in relation to zinc concentration in toenails. British Journal of Nutrition (2003), 89, 673–678.
- The association of toenail Zn, which integrates dietary Zn intake over 3 to 12 months, with the risk of a first myocardial infarction was assessed - toenail Zn levels were not significantly associated with acute myocardial infarction – not relevant

Ozsobaci et al.2019. Protective Effects of Zinc on 2.45 GHz Electromagnetic Radiation-Induced Oxidative Stress and Apoptosis in HEK293 Cells. Biological Trace Element Research. 17 July 2019.
- In vitro study in human embryo kidney (HEK) cells – not relevant

Schrag et al. 2011. Iron, zinc and copper in the Alzheimer’s disease brain: a quantitative meta-analysis. Some insight on the influence of citation bias on scientific opinion. Prog Neurobiol. 2011 August; 94(3): 296–306.
- By using meta-analysis and systemic review methodologies a wide-spread misconception could be identified in AD literature that iron, and to a lesser degree zinc and copper, levels are increased in AD brain. The data on zinc levels in the neocortex was heterogeneous and no clear explanation for the heterogeneity could be deduced from the meta-data – no useful information

Smith et al. 2019. Inadequate Zinc Intake in India: Past, Present, and Future. Food and Nutrition Bulletin 2019, Vol. 40(1) 26-40.
- An assessment of the historical prevalence of inadequate zinc intake in India, as well as an estimation of the future prevalence attributable to rising CO2 is described – not relevant

Stenberg and Roth 2015. Zinc is the modulator of the calcium-dependent activation of post-translationally acting thiol-enzymes in autoimmune diseases. Medical Hypotheses 2015. 84(4), 331-335.
- Post‐translational modifications are of potential interest in autoimmune diseases. The in vivo activation of calcium‐dependent thiol‐enzymes catalyzing these alterations, such as the TGs and the PADs, is crucial for this pathway. The hypothesis was postulated that zinc is the modulator of this key function – no useful information

Swaminath et al. 2019. Combined mineral intakes and risk of colorectal cancer in postmenopausal women. Cancer Epidemiol Biomarkers Prev. 2019 February; 28(2): 392–399.
- Higher calcium, magnesium, manganese, zinc, selenium, potassium, and iodine intakes, combined with lower iron, copper, phosphorus, and sodium intakes may be associated with lower risk of colo-rectal cancer; no specific information on zinc – not relevant

Villalpando et al. 2003. Iron, zinc and iodide status in Mexican children under 12 years and women 12-49 years of age. A probabilistic national survey. Salud pública de méxico / vol.45, suplemento 4 de 2003.
- Iron, zinc and iodide deficiency in Mexican children below 12 years and woman of child-bearing potential (WOCBP) and its association with some dietary and socio-demographic variables were explored; no correlation to health status was made – no useful information

Wen et al. 2019. Associations of multiple plasma metals with the risk of ischemic stroke A case-control study. Environment International 125 (2019) 125–134.
- higher plasma concentrations of aluminium, arsenic, and cadmium, and lower concentrations of iron and selenium may increase the risk of IS; no association for zinc – not relevant