Zinc in the diet of healthy preschool and school children

[Effect of marginal zinc deficiency on humoral immunity in rats]

The purpose of this experiment was to examine the effects of a marginal zinc deficiency on serum immunoglobulin (Ig) IgM and IgG1 levels. 60 weanling female Sprague-Dawley rats were divided into six groups of ten animals each. Two control groups (73.7 ppm Zn) and two zinc-deficient groups (4.3 ppm Zn) were fed a semisynthetic casein diet ad libitum. The animals of two further groups received the control diet (73.7 ppm Zn) pair-fed to the zinc-deficient animals. After 15 days the rats of one group of each treatment were infected i.m. with a single injection (0.2 ml) of a bovine enterovirus, apathogenous to rats. 3 weeks later, all rats were anesthetized with ether and decapitated. Infection of the rats with the bovine enterovirus had no effect on the serum immunoglobulin level. The marginal zinc deficiency did not alter the IgM and IgG1 serum concentrations at all either. It remains to be examined whether other Ig-classes will react to marginal zinc deficiency. Also, the effect of severe zinc deficiency on the humoral immune system must be studied.

Requirement of zinc in human subjects

Essentiality of zinc in nutrition of higher animals was established in 1934. Dietary zinc deficiency in humans was recognized in 1961. Dietary requirements for zinc have been estimated factorially and by balance studies. Factors that influence dietary zinc requirement include dietary and other substances that either facilitate or inhibit absorption and retention of zinc; and metabolic phenomena that influence retention or excretion of the element. These determinants must be considered in estimating the requirement and the recommended dietary allowance for this essential element. An approach that has been used to assess requirement is the measurement of dietary zinc retention by men fed diets providing sufficient energy to meet the needs of each individual and containing other nutrients in proportion to energy content. By measurement of chemical balance and subsequent analysis of the data by multiple regression, dietary factors influencing requirement have been identified and amounts of dietary zinc essential for needs calculated. Using this approach, 83% of the variance (P less than 0.0001) in requirement was accounted for by the dietary content of phosphorus and nitrogen when data from 157 twenty-eight to thirty day studies were analyzed. The equation, Intake = 1.466 + 0.23 (Zn balance) + 5.19 (P intake) + 0.40 (N intake) - 0.30 (P intake - 1.389) (N intake - 14.646), was used to estimate zinc requirement of persons who participated in the most recent USDA Food Consumption Survey. For all age groups, ages 9 to greater than 75y, males and females, the mean (range) difference between the estimated intakes and calculated requirements were: males 1.5% (-6.5 to + 8.1), females 11.3% (- 1.1 to + 20.3). Thus, mean intakes were generally within the 95% confidence limits of the estimated requirements. Of some interest was the finding that the mean intake of none of the groups was equivalent to the Recommended Dietary Allowance. The mean intake of males ranged from 9.32 mg in men 75y and older to 13.53 mg in persons 15-18y. The mean intake of the females ranged from 7.04 mg in women 75y and older to 9.22 mg in persons 12-14 y.

Zinc status and growth of children undergoing treatment for phenylketonuria

Children with phenylketonuria (PKU) are treated with semi-synthetic diets restricted in phenylalanine. Low-phenylalanine or phenylalanine-free formulae provide the majority of protein and energy in the diet while phenylalanine requirements are met by low-protein natural foods. Because of the restriction of natural protein sources in this diet, the study assessed the zinc nutrition of 22 treated children with PKU (aged from 1 month to 8 1/2 years) and correlated linear growth with zinc status. The mean (+/- SE) plasma zinc concentration of the PKU population was 66.6 +/- 3.3 micrograms/dl. The mean (+/- SE) hair zinc concentration was 70.2 +/- 11.5 micrograms/g. The mean plasma and hair zinc concentrations of the PKU population were significantly different (p less than 0.05) when compared with mean (+/- SE) normal values of 84.2 +/- 2.9 micrograms/dl and 130.7 +/- 8.3 micrograms/g, respectively. The mean (+/- SD) dietary zinc intake of 10 PKU patients was 8.56 +/- 2.68 mg/day. No significant differences (p less than 0.123) were found when the mean zinc intake was compared with National Academy of Sciences Recommended Dietary Allowance for age of 10 mg/day. No significant correlations were found when plasma and hair zinc concentrations were plotted with height percentiles. Further studies are required to assess the effects of zinc supplementation and the bioavailability of zinc from low-phenylalanine diets.

Zinc and copper status of treated children with phenylketonuria

Children with phenylketonuria (PKU) are treated with semi-synthetic diets restricted in phenylalanine. Low or phenylalanine-free formulae provide the majority of protein and energy in the diet while phenylalanine requirements are met by low-protein natural foods. Because of the restriction of natural protein sources in this diet, the study assessed the zinc and copper nutriture of treated children with PKU and correlated linear growth with zinc status. The plasma zinc of the PKU population was 66.6 +/- 3.3 micrograms/dl (mean +/- SEM). The hair zinc was 70.2 +/- 11.5 micrograms/g (mean +/- SEM). The mean plasma and hair zinc of the PKU population were significantly different (p less than 0.05) when compared to normal values of 84.2 +/- 2.9 micrograms/dl and 130.7 +/- 8.3 micrograms/g (mean +/- SEM), respectively. The dietary zinc intake of 10 PKU patients was 8.56 +/- 2.68 mg/day (mean +/- SD). No significant differences (p less than 0.123) were found when the mean zinc intake was compared with recommended dietary allowances for age of 10 mg/day. No significant correlations were found when plasma and hair zinc were plotted with height percentiles. Plasma copper of the PKU subjects (87.6 +/- 6.6 micrograms/dl, mean +/- SEM) was significantly less than that of normal young children (121.5 +/- 3.1 micrograms/dl, mean +/- SEM) despite a copper intake a 1.45 +/- 0.35 mg/day (mean +/- SD).