The assessment of zinc status: a personal view

Zinc supplementation for improving pregnancy and infant outcome

BACKGROUND

It has been suggested that low serum zinc levels may be associated with suboptimal outcomes of pregnancy, such as prolonged labour, atonic postpartum haemorrhage, pregnancy-induced hypertension, preterm labour and post-term pregnancies, although these associations have not yet been established. This is an update of a review first published in 1997 and subsequently updated in 2007, 2012 and 2015.

OBJECTIVES

1. To compare the effects on maternal, fetal, neonatal and infant outcomes in healthy pregnant women receiving zinc supplementation versus no zinc supplementation, or placebo. 2. To assess the above outcomes in a subgroup analysis reviewing studies performed in women who are, or are likely to be, zinc-deficient.

SEARCH METHODS

For this update, we searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (3 July 2020), and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised trials of zinc supplementation versus no zinc supplementation or placebo administration during pregnancy, earlier than 27 weeks' gestation. We excluded quasi-randomised controlled trials. We intended to include studies presented only as abstracts, if they provided enough information or, if necessary, by contacting authors to analyse them against our criteria; we did not find any such studies.

DATA COLLECTION AND ANALYSIS

Three review authors applied the study selection criteria, assessed trial quality and extracted data. When necessary, we contacted study authors for additional information. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

For this update, we included 25 randomised controlled trials (RCTs) involving over 18,000 women and their babies. The overall risk of bias was low in half of the studies. The evidence suggests that zinc supplementation may result in little or no difference in reducing preterm births (risk ratio (RR) 0.87, 95% confidence interval (CI) 0.74 to 1.03; 21 studies, 9851 participants; low-certainty evidence). Further, zinc supplementation may make little or no difference in reducing the risk of stillbirth (RR 1.22, 95% CI 0.80 to 1.88; 7 studies, 3295 participants; low-certainty evidence), or perinatal deaths (RR 1.10, 95% CI 0.81 to 1.51; 2 studies, 2489 participants; low-certainty evidence). It is unclear whether zinc supplementation reduces neonatal death, because the certainty of the evidence is very low. Finally, for other birth outcomes, zinc supplementation may make little or no difference to mean birthweight (MD 13.83, 95% CI -15.81 to 43.46; 22 studies, 7977 participants; low-certainty evidence), and probably makes little or no difference in reducing the risk of low birthweight (RR 0.94, 95% CI 0.79 to 1.13; 17 studies, 7399 participants; moderate-certainty evidence) and small-for-gestational age babies when compared to placebo or no zinc supplementation (RR 1.02, 95% CI 0.92 to 1.12; 9 studies, 5330 participants; moderate-certainty evidence). We did not conduct subgroup analyses, as very few studies used normal zinc populations.

AUTHORS' CONCLUSIONS

There is not enough evidence that zinc supplementation during pregnancy results in improvements in maternal or neonatal outcomes. Future research to address ways of improving the overall nutritional status of pregnant women, particularly in low-income regions, and not looking at zinc in isolation, should be an urgent priority.

Zinc and infant nutrition

Zinc is essential for a wide variety of cellular processes in all cells. It is a critical dietary nutrient, particularly in the early stages of life. In the early neonatal period, adequate sources of zinc can be obtained from breast milk. In rare circumstances, the mammary gland produces zinc deficient milk that is potentially lethal for exclusively breast-fed infants. This can be overcome by zinc supplementation to the infant. Alterations to key zinc transporters provide insights into the mechanisms of cellular zinc homeostasis. The bioavailability of zinc in food depends on the presence of constituents that may complex zinc. In many countries, zinc deficiency is a major health issue due to poor nourishment. Young children are particularly affected. Zinc deficiency can impair immune function and contributes to the global burden of infectious diseases including diarrhoea, pneumonia and malaria. Furthermore, zinc deficiency may extend its influence across generations by inducing epigenetic effects that alter the expression of genes. This review discusses the significance of adequate zinc nutrition in infants, factors that influence zinc nutrition, the consequences of zinc deficiency, including its contribution to the global burden of disease, and addresses some of the knowledge gaps in zinc biology.

Zinc supplementation for improving pregnancy and infant outcome

BACKGROUND

It has been suggested that low serum zinc levels may be associated with suboptimal outcomes of pregnancy such as prolonged labour, atonic postpartum haemorrhage, pregnancy-induced hypertension, preterm labour and post-term pregnancies, although many of these associations have not yet been established.

OBJECTIVES

To assess the effects of zinc supplementation in pregnancy on maternal, fetal, neonatal and infant outcomes.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 October 2014) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised trials of zinc supplementation in pregnancy. We excluded quasi-randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Three review authors applied the study selection criteria, assessed trial quality and extracted data. When necessary, we contacted study authors for additional information. The quality of the evidence was assessed using GRADE.

MAIN RESULTS

We included 21 randomised controlled trials (RCTs) reported in 54 papers involving over 17,000 women and their babies. One trial did not contribute data. Trials were generally at low risk of bias. Zinc supplementation resulted in a small reduction in preterm birth (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.76 to 0.97 in 16 RCTs; 16 trials of 7637 women). This was not accompanied by a similar reduction in numbers of babies with low birthweight (RR 0.93, 95% CI 0.78 to 1.12; 14 trials of 5643 women). No clear differences were seen between the zinc and no zinc groups for any of the other primary maternal or neonatal outcomes, except for induction of labour in a single trial. No differing patterns were evident in the subgroups of women with low versus normal zinc and nutrition levels or in women who complied with their treatment versus those who did not. The GRADE quality of the evidence was moderate for preterm birth, small-for-gestational age, and low birthweight, and low for stillbirth or neonatal death and birthweight.

AUTHORS' CONCLUSIONS

The evidence for a 14% relative reduction in preterm birth for zinc compared with placebo was primarily represented by trials involving women of low income and this has some relevance in areas of high perinatal mortality. There was no convincing evidence that zinc supplementation during pregnancy results in other useful and important benefits. Since the preterm association could well reflect poor nutrition, studies to address ways of improving the overall nutritional status of populations in impoverished areas, rather than focusing on micronutrient and or zinc supplementation in isolation, should be an urgent priority.

Oral zinc for arterial and venous leg ulcers

BACKGROUND

Leg ulcers affect up to one percent of people at some time in their life. Leg ulceration is chronic in nature and ulcers may be present for months or even years without healing. After healing there is a high risk of recurrence. Treatments include wound dressings alongside the treatment of underlying medical problems such as poor blood supply, infection and poor nutrition.

OBJECTIVES

To assess the effectiveness of oral zinc in healing arterial or venous leg ulcers.

SEARCH METHODS

For this seventh update we searched The Cochrane Wounds Group Specialised Register (searched 02 September 2014) and The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 8). In the original version of the review a company manufacturing zinc sulphate tablets was asked for references to relevant trials.

SELECTION CRITERIA

Randomised controlled trials comparing oral zinc sulphate with placebo or no treatment in people with arterial or venous leg ulcers were eligible for inclusion. There were no restrictions on date or language of publication. The main outcome measure used was complete healing of the ulcers. Trials were eligible for inclusion if they measured ulcer healing objectively by documenting time to complete healing, proportion of ulcers healed during the study, or healing rates of ulcers.

DATA COLLECTION AND ANALYSIS

All data extraction and assessment of trial quality was done by both authors independently.

MAIN RESULTS

Six small trials (183 participants) were eligible for inclusion. Four trials considered people with venous ulcers, one trial involved people with arterial ulcers and one people with mixed aetiology ulcers. Serum zinc was measured in four trials and four trials compared oral zinc sulphate with placebo in people with venous ulcers; pooling these trials indicated no statistically significant difference between the two groups for healing (RR 1.22, 95%CI 0.88 to 1.68). Overall, there is no evidence that oral zinc increases the healing of arterial or venous leg ulcers.

AUTHORS' CONCLUSIONS

Oral zinc sulphate does not appear to aid the healing of arterial and venous leg ulcers, however all included studies were small and at unclear risk of bias (due to poor reporting).

Zinc deficiency and its inherited disorders -a review

Zinc is an essential trace element required by all living organisms because of its critical roles both as a structural component of proteins and as a cofactor in enzyme catalysis. The importance of zinc in human metabolism is illustrated by the effects of zinc deficiency, which include a diminished immune response, reduced healing and neurological disorders. Furthermore, nutritional zinc deficiency can be fatal in newborn or growing animals. While zinc deficiency is commonly caused by dietary factors, several inherited defects of zinc deficiency have been identified. Acrodermatitis enteropathica is the most commonly described inherited condition found in humans. In several of the few cases that have been reported, this disorder is associated with mutations in the hZIP4 gene, a member of the SLC39 family, whose members encode membranebound putative zinc transporters. Mutations in other members of this family or in different genes may account for other cases of acrodermatitis in which defects in hZIP4 have not been detected. Another inherited form of zinc deficiency occurs in the lethal milk mouse, where a mutation in ZnT4 gene, a member of the SLC30 family of transmembrane proteins results in impaired secretion of zinc into milk from the mammary gland. A similar disorder to the lethal milk mouse occurs in humans. In the few cases studied, no changes in ZnT4 orthologue, hZnT4, were detected. This, and the presence of several minor phenotypic differences between the zinc deficiency in humans and mice, suggests that the human condition is caused by defects in genes that are yet to be identified. Taking into account the fact that there are no definitive tests for zinc deficiency and that this disorder can go undiagnosed, plus the recent identification of multiple members of the SCL30 and SLC39, it is likely that mutations in other genes may underlie additional inherited disorders of zinc deficiency.

Oral zinc for arterial and venous leg ulcers

BACKGROUND

Leg ulcers affect up to one percent of people at some time in their life. Leg ulceration is chronic in nature with ulcers being present for months and in some cases years without healing, and with a high risk of recurrence. Management approaches include dressings and the treatment of underlying medical problems such as malnutrition, lack of minerals and vitamins, poor blood supply or infection.

OBJECTIVES

To assess the effectiveness of oral zinc in healing arterial or venous leg ulcers.

SEARCH METHODS

For this sixth update we searched The Cochrane Wounds Group Specialised Register (searched 17 May 2012); The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 5); Ovid MEDLINE (2010 to May Week 2 2012); Ovid MEDLINE (In-Process & Other Non-Indexed Citations May 16, 2012); Ovid EMBASE (2010 to 2012 Week 19); and EBSCO CINAHL (2010 to May 2 2012). In the original version of the review a company manufacturing zinc sulphate tablets was asked for references to relevant trials.

SELECTION CRITERIA

Randomised controlled trials comparing oral zinc sulphate with placebo or no treatment in people with arterial or venous leg ulcers were eligible for inclusion. There were no restrictions on date or language of publication. The main outcome measure used was complete healing of the ulcers. Trials were eligible for inclusion if they measured ulcer healing objectively by documenting time to complete healing, proportion of ulcers healed during the study, or healing rates of ulcers.

DATA COLLECTION AND ANALYSIS

All data extraction and assessment of trial quality were done by both authors independently.

MAIN RESULTS

Six small trials (183 participants) were eligible for inclusion. Four trials considered people with venous ulcers, one trial arterial ulcers and one people with mixed ulcers. In four trials, serum zinc was measured at baseline or during the trial. Pooling the four trials that compared oral zinc sulphate with placebo in people with venous ulcers showed no statistically significant difference between the two group (RR 1.22, 95%CI 0.88 to 1.68). Overall, there was no evidence of a beneficial effect of treatment with zinc sulphate on the number of ulcers healed.

AUTHORS' CONCLUSIONS

Oral zinc sulphate does not appear to aid healing of arterial and venous leg ulcers, however all included studies were small and of mediocre quality.

Zinc supplementation for improving pregnancy and infant outcome

BACKGROUND

It has been suggested that low serum zinc levels may be associated with suboptimal outcomes of pregnancy such as prolonged labour, atonic postpartum haemorrhage, pregnancy-induced hypertension, preterm labour and post-term pregnancies, although many of these associations have not yet been established.

OBJECTIVES

To assess the effects of zinc supplementation in pregnancy on maternal, fetal, neonatal and infant outcomes.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 September 2011) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised trials of zinc supplementation in pregnancy. We excluded quasi-randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Three review authors applied the study selection criteria, assessed trial quality and extracted data. When necessary, we contacted study authors for additional information.

MAIN RESULTS

We included 20 randomised controlled trials (RCTs) reported in 51 papers involving over 15,000 women and their babies. Trials were generally at low risk of bias. Zinc supplementation resulted in a small but significant reduction in preterm birth (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.76 to 0.97 in 16 RCTs; 16 trials of 7637 women). This was not accompanied by a similar reduction in numbers of babies with low birthweight (RR 0.93, 95% CI 0.78 to 1.12; 14 trials of 5643 women). No significant differences were seen between the zinc and no zinc groups for any of the other primary maternal or neonatal outcomes, except for induction of labour in a single trial. No differing patterns were evident in the subgroups of women with low versus normal zinc and nutrition levels or in women who complied with their treatment versus those who did not.

AUTHORS' CONCLUSIONS

The evidence for a 14% relative reduction in preterm birth for zinc compared with placebo was primarily represented by trials involving women of low income and this has some relevance in areas of high perinatal mortality. There was no convincing evidence that zinc supplementation during pregnancy results in other useful and important benefits. Since the preterm association could well reflect poor nutrition, studies to address ways of improving the overall nutritional status of populations in impoverished areas, rather than focusing on micronutrient and or zinc supplementation in isolation, should be an urgent priority.

Chromium, selenium, and zinc multimineral enriched yeast supplementation ameliorates diabetes symptom in streptozocin-induced mice

Chromium, selenium, and zinc malnutrition has been implicated in the pathogenesis of diabetic mellitus. This study aims to investigate the effects of novel multiminerals-enriched yeast (MMEY) which are minerals supplementation containing elevated levels of chromium, selenium, and zinc simultaneously in a diabetic animal model. Streptozocin-induced diabetic male Balb/c mice (n = 80) were randomly divided into diabetes control group and three treatment groups. They were administrated oral gavages with low, medium, or high doses of MMEY, respectively. Meanwhile, healthy male Balb/c mice (n = 40) of the same body weight were randomly assigned into normal control group and high dose of MMEY control group. After 8 weeks duration of treatment, the animals were sacrificed by cervical dislocation. Serum glucose concentrations, lipid profiles, oxidative/antioxidant, and immunity status were determined. No significant adverse effects were observed in the high-dose MMEY control group. Treatment of the diabetic mice with medium- or high-dose MMEY significantly decreased serum glucose, triglyceride, total cholesterol, and malondialdehyde and increased high-density lipoprotein cholesterol, glutathione, and the activities of superoxide dismutase and glutathione peroxidase. In addition, MMEY ameliorated the pathological damage of the pancreatic islets, elevated the thymus or spleen coefficient, and increased the expressions of interleukin-2 and -4 in spleen lymphocytes compared with unsupplemented diabetic mice. In conclusion, these results indicate that supplemental MMEY inhibits hyperglycemia, abates oxidative stress, modulates disorders of lipid metabolism, and reduces the impairment of immune function in diabetic mice; especially notable are the protective effects of medium doses of MMEY on the islet cells of diabetic mice.

Zinc: an essential but elusive nutrient

Zinc is essential for multiple aspects of metabolism. Physiologic signs of zinc depletion are linked with diverse biochemical functions rather than with a specific function, which makes it difficult to identify biomarkers of zinc nutrition. Nutrients, such as zinc, that are required for general metabolism are called type 2 nutrients. Protein and magnesium are examples of other type 2 nutrients. Type 1 nutrients are required for one or more specific functions: examples include iron, vitamin A, iodine, folate, and copper. When dietary zinc is insufficient, a marked reduction in endogenous zinc loss occurs immediately to conserve the nutrient. If zinc balance is not reestablished, other metabolic adjustments occur to mobilize zinc from small body pools. The location of those pools is not known, but all cells probably have a small zinc reserve that includes zinc bound to metallothionein or zinc stored in the Golgi or in other organelles. Plasma zinc is also part of this small zinc pool that is vulnerable to insufficient intakes. Plasma zinc concentrations decline rapidly with severe deficiencies and more moderately with marginal depletion. Unfortunately, plasma zinc concentrations also decrease with a number of conditions (eg, infection, trauma, stress, steroid use, after a meal) due to a metabolic redistribution of zinc from the plasma to the tissues. This redistribution confounds the interpretation of low plasma zinc concentrations. Biomarkers of metabolic zinc redistribution are needed to determine whether this redistribution is the cause of a low plasma zinc rather than poor nutrition. Measures of metallothionein or cellular zinc transporters may fulfill that role.

Zinc supplementation for the treatment or prevention of disease: current status and future perspectives

Zinc is a nutritionally essential trace element, and thus zinc deficiency may severely affect human health. Many studies were published in which the effect of nutritional zinc supplementation on the incidence or severity of a certain disease was investigated. This review summarizes the main observations and aims to evaluate the use of nutritional zinc supplementation for prevention and treatment of human disease.

Zinc supplementation for improving pregnancy and infant outcome

BACKGROUND

It has been suggested that low serum zinc levels may be associated with suboptimal outcomes of pregnancy such as prolonged labour, atonic postpartum haemorrhage, pregnancy-induced hypertension, preterm labour and post-term pregnancies, although many of these associations have not yet been established.

OBJECTIVES

To assess the effects of zinc supplementation in pregnancy on maternal, fetal, neonatal and infant outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (February 2007).

SELECTION CRITERIA

Randomised or quasi-randomised trials of zinc supplementation in pregnancy.

DATA COLLECTION AND ANALYSIS

Two review authors applied the study selection criteria, assessed trial quality and extracted data. When necessary, study authors were contacted for additional information.

MAIN RESULTS

We included 17 randomised controlled trials (RCTs) involving over 9000 women and their babies. Zinc supplementation resulted in a small but significant reduction in preterm birth (relative risk (RR) 0.86, 95% confidence interval (CI) 0.76 to 0.98 in 13 RCTs; 6854 women). This was not accompanied by a similar reduction in numbers of babies with low birthweight (RR 1.05 95% CI 0.94 to 1.17; 11 studies of 4941 women). No significant differences were seen between the zinc and no zinc groups for any of the other primary maternal or neonatal outcomes, except for a small effect favouring zinc for caesarean section (four trials with high heterogeneity) and for induction of labour in a single trial. No differing patterns were evident in the subgroups of women with low versus normal zinc and nutrition levels or in women who complied with their treatment versus those who did not.

AUTHORS' CONCLUSIONS

The 14% relative reduction in preterm birth for zinc compared with placebo was primarily in the group of studies involving women of low income and this has some relevance in areas of high perinatal mortality. There was no convincing evidence that zinc supplementation during pregnancy results in other useful and important benefits. Since the preterm association could well reflect poor nutrition, studies to address ways of improving the overall nutritional status of populations in impoverished areas, rather than focusing on micronutrient and or zinc supplementation in isolation, should be an urgent priority.

Evidence that diabetes mellitus favors impaired metabolism of zinc, copper, and selenium in chronic pancreatitis

Diabetes mellitus, a common complication of chronic pancreatitis, can disturb the metabolism of zinc, copper, and selenium. We analyzed the effects of hyperglycemia, malabsorption, and dietary intake on these factors in 35 men with alcohol-induced chronic pancreatitis complicated by insulin-treated diabetes mellitus (CP-D), 12 men with chronic pancreatitis but no diabetes (nondiabetic CP), 25 men with type 1 diabetes mellitus (type 1 DM), and 20 control subjects. Diabetes due to chronic pancreatitis was associated with decreased plasma zinc and selenium concentrations and with increased urinary copper excretion. Of the chronic pancreatitis patients, 17% had low plasma zinc, and 41% of them had low plasma selenium. None of the type 1 diabetic patients had low plasma concentrations of zinc, but 12% of them had a low selenium concentration. Hyperglycemia, as assessed by fasting plasma glucose and by plasma HbAlc, was responsible for the increased zinc excretion and the decreased superoxide dismutase activity. The perturbations of the copper, selenium, and zinc metabolism were particularly pronounced in subjects with chronic pancreatitis plus diabetes mellitus. We have yet to determine whether the differences in trace-element status contribute to the clinical expression of the disease.

Zinc and the Eye

Zinc, a trace element that influences cell metabolism through a variety of mechanisms, appears to play an integral role in maintaining normal ocular function. This element is present in high concentrations in ocular tissue, particularly in retina and choroid. Zinc deficiency has been shown in a number of species to result in a variety of gross, ultrastructural and electrophysiologic ocular manifestations. The physiological functions for zinc have been studied predominantly in retina and retinal pigment epithelium where zinc is believed to interact with taurine and vitamin A. modify photoreceptor plasma membranes, regulate the light-rhodopsin reaction, modulate synaptic transmission and serve as an antioxidant. Suboptimal zinc status in North America may influence the development and progression of several chronic eye diseases. Zinc supplementation trials and epidemiological studies have produced conflicting results concerning the role of zinc in age-related macular degeneration. Additional well-controlled supplementation trials are indicated to clarify the role of zinc in this disease. Future investigations must also expand our understanding of the mechanisms by which zinc regulates ocular morphology and function.

Assessment of marginal zinc status in humans

The assessment of marginal zinc status is problematic. Currently, there is no universally accepted single measure to assess zinc status in humans. The development of a reliable measure of marginal or moderate zinc status would be useful for a variety of purposes. For example, a simple, yet sensitive and accurate measure of zinc nutritional status is critically needed to further our limited understanding of the possible associations between zinc status and the risk of developing various chronic diseases and in predicting favorable health outcomes in patient populations. A convenient and reliable zinc assessment tool is needed to identify subpopulations who are at a risk of zinc deficiency and as an objective guidepost to determine the need for initiation of zinc supplementation or zinc fortification of the food supply, as well in the refinement of recommendations of dietary zinc allowances. In frank zinc deficiency, clinical signs and static measures of zinc concentrations in a variety of readily available tissues, such as plasma, various blood cell types and hair, may uniformly confirm the presence of depleted body zinc stores. However, in general, the relative insensitivity or imprecision of these measurements has resulted in general disappointment in their use to assess marginal zinc status. Therefore, the search continues to find a useful and reliable marker of marginal zinc deficiency. In an attempt to speculate on possible future developments in the zinc status assessment field, a number of new and potentially promising approaches to this problem are highlighted.

Oral zinc for arterial and venous leg ulcers

BACKGROUND

Leg ulcers affect up to 1 per cent of people at some time in their life. Management includes care of the ulcer using dressings and treatment of underlying medical problems such as malnutrition, lack of minerals, vitamins, poor blood supply or infection.

OBJECTIVES

To assess the effectiveness of oral zinc in healing arterial or venous leg ulcers.

SEARCH STRATEGY

Searches of 19 databases, hand searching of journals and conference proceedings from 1948 onwards, and examination of bibliographies. The company manufacturing zinc sulphate tablets was asked for references to relevant trials.

SELECTION CRITERIA

Randomised controlled trials comparing oral zinc sulphate with placebo or no treatment in patients with arterial or venous leg ulcers. There was no restriction on date or language. The main outcome measure used was complete healing of the ulcers. Trials were eligible for inclusion if they measured ulcer healing objectively, by time to complete healing, proportion of ulcers healed during the study, or healing rates of ulcers.

DATA COLLECTION AND ANALYSIS

All data extraction and assessment of trial quality were done by both authors independently.

MAIN RESULTS

There were six eligible trials. All are small and serum zinc was measured at baseline or during the trial in 4 trials. Overall there is no evidence of a beneficial effect of treatment with zinc sulphate on the number of ulcers healed at the end of the trials. There is some evidence that oral zinc might have a beneficial effect on healing of venous ulcers in people with a 'low' serum zinc level at baseline.

REVIEWER'S CONCLUSIONS

Overall, oral zinc sulphate does not appear to aid healing of leg ulcers, although it might be beneficial in those with venous leg ulcers and low serum zinc. Further research is needed to ascertain the serum zinc concentration below which treatment with zinc might be beneficial, and the dose required. [This abstract was prepared centrally]

Zinc in primary teeth from children in Norway

Human primary teeth have been used as indicators of exposure to several heavy metals both in Norway and elsewhere. Local dentists in all 19 counties of Norway collected 2747 primary teeth during 1990-1994. Samples of tooth powder from whole, ground teeth were analyzed for zinc concentration by flame atomic absorption spectrophotometry. The overall geometrical mean was 144.5 micrograms of Zn/g of tooth substance (S.D. = 1.6). The result represents a small increase (5.2%) compared with a similar investigation in the 1970s. However, the mean zinc concentrations in the geographically matching parts of the two materials did not differ significantly. The variation in tooth zinc concentrations between the different counties declined from the 1970s to the 1990s. We found no correlation between the tooth zinc concentration and available environmental data on zinc in drinking-water, discharge of zinc from industrial point sources or population density in the same geographical areas. The zinc concentrations varied significantly with caries status, tooth type and root length. Few samples had a zinc concentration below 90 micrograms/g, indicating that most children consume sufficient zinc. Some very high values could not immediately be explained, but may be caused by contamination from zinc-containing dental restorations.

Levels of polyunsaturated fatty acids in tissues from zinc-deficient rats fed a linseed oil diet

The effect of zinc deficiency on the levels of n-6 and n-3 polyunsaturated fatty acids (PUFA) in lipids from tissues of rats fed a diet containing linseed oil was investigated. Rats were fed either a control diet (25 mg Zn/kg) or a zinc-deficient diet (0.8 mg Zn/kg) for 10 d. To avoid energy and nutrient deficiency, 11.6 g of diet per day was administered by gastric tube. At the end of the experiment, rats fed the zinc-deficient diet had drastically reduced plasma zinc concentration and alkaline phosphatase activity consistent with severe zinc deficiency in these rats. Zinc-deficient rats had higher levels of n-3 PUFA, in particular eicosapentaenoic acid (EPA), and lower levels of n-6 PUFA, in particular linoleic acid, in liver and plasma phosphatidylcholine (PC) and in erythrocyte membrane total lipids than did control rats. By contrast, the levels of n-3 PUFA in PC from testes and heart, and in phosphatidylethanolamine (PE) from liver, testes and heart, were only slightly different between zinc-deficient and control rats. The study suggests that desaturation of alpha-linolenic acid is not inhibited by zinc deficiency, and that in zinc-deficient rats, n-3 PUFA preferentially incorporated into phospholipids at the expense of n-6 PUFA, especially EPA into PC. The study also shows that the effect of zinc deficiency on PUFA levels is different for PC and PE in rat tissues.

Zinc intake, zinc status and growth in a longitudinal study of healthy Danish infants

Mild, growth-limiting zinc deficiency might be prevalent in otherwise healthy infants according to recent studies. We examined zinc intake and status in 91 healthy term infants from birth to 12 months, as part of the Copenhagen Cohort Study on Infant Nutrition and Growth. Zinc intake was recorded monthly and the amount of zinc absorbed was estimated. These estimates were below recently published FAO/WHO/IAEA values for basal requirements in 68%, 62% and 14% of the infants at 2, 4 and 9 months of age, respectively. Serum zinc decreased significantly (p < 0.01) from 10.6 mumol/l at 6 months to 8.4 mumol/l at 9 months of age (normal range 10-18 mumol/l). Erythrocyte metallothionein values, a tentative indicator of long-term zinc status, decreased significantly from 2 to 6 months (p < 0.001) and from 6 to 9 months (p < 0.01). Serum zinc at 9 months was positively associated with growth velocity during the period from 6 to 9 months (weight: p = 0.05; knee-heel length: p = 0.002). The results provide descriptive data on zinc intake and zinc status in healthy Danish infants. Although some of our data suggest suboptimal zinc status during late infancy, evidence for this can only be obtained through a randomized intervention study.

Refrigeration of blood samples prior to separation is essential for the accurate determination of plasma or serum zinc concentrations

An evaluation of refrigeration (7 degrees C) to prevent falsely high plasma or serum zinc concentrations owing to elapsed time between blood collection and centrifugation was performed. At room temperature (23 degrees C), both plasma and serum zinc concentrations increased significantly, if blood samples were stored uncentrifuged. Plasma zinc concentrations increased 6.3% at 1 h and 40.7% at 24 h, whereas serum zinc concentrations increased only 0.9% at 1 h and 12.5% at 24 h at room temperature. When blood samples were stored uncentrifuged in the refrigerator for up to 24 h, there were no significant increases in zinc concentrations in either plasma or serum. These findings suggest that plasma or serum separation should be performed immediately after blood drawing to obtain accurate zinc concentrations, and if this is not feasible, the samples should be immediately refrigerated and separation performed within eight hours.

Is cow's milk suitable for the dietary supplementation of rural Gambian children? 2. Patterns of cow's milk intake

Cow's milk has been advocated as a source of supplementary diet for children in many parts of the developing world. The frequency and forms of cow's milk intake and the factors regulating its availability and consumption by 507 children aged up to 6 years in three Gambian villages were measured. Nineteen per cent of mothers did not give cow's milk to their children. Of 413 children taking cow's milk, 41% consumed it only once a week, 32% two to four times a week, 19% once a day and 8% more than once a day. Eighty per cent of children took both fresh and sour milk. Forty-one per cent of infants up to 1 year old received cow's milk at some time. There was a decrease with age in the proportion of children taking fresh milk and a rise with age in the proportion taking sour milk alone (p < 0.001) and both forms of milk. Only 2% of children were reported to have an adverse reaction to fresh cow's milk. The main factors affecting intake were the availability of money and milk. The consumption of cow's milk in early life is common and free of adverse effects. When it is available, it should be used to supplement the diet of the weaned child.