Interrelationships of key variables of human zinc homeostasis: relevance to dietary zinc requirements.

Currently, estimates of human zinc requirements depend primarily on a factorial approach. The availability of tracer techniques employing zinc stable isotopes has facilitated the acquisition of data on major variables of zinc homeostasis in addition to those that can be measured with careful metabolic balance techniques. These data have promising potential to facilitate and improve the factorial approach. The thesis proposed in this paper is that realistic estimations of dietary zinc requirements by a factorial approach require attention to the dynamic interrelationships between major variables of zinc homeostasis. This applies especially to the positive relationship between endogenous fecal zinc and total absorbed zinc, which is the essential starting point in estimating physiologic and, from there, dietary requirements.

Human zinc deficiency.

The objective of this paper is to provide a current overview of the significance of zinc in human nutrition. To achieve this, the following issues are addressed: (1) the biochemistry and biology of zinc in the context of their relevance to zinc in human nutrition and to our understanding of the complexity and practical importance of human zinc deficiency; (2) the history of our understanding of human zinc deficiency with an emphasis both on its brevity and on notable recent progress; (3) the clinical spectrum of severe zinc deficiency; (4) the lack of ideal biomarkers for milder zinc deficiency states, with the consequent dependence on randomized, placebo-controlled intervention studies to ascertain their prevalence and clinical consequences, including growth delay, diarrhea, pneumonia, other infections, disturbed neuropsychological performance and abnormalities of fetal development; (5) the public health significance of human zinc deficiency in the developing world; (6) reasons for concern and unanswered questions about zinc nutriture in the United States; (7) the need for better understanding of human zinc metabolism and homeostasis (including its limitations) at a molecular, cellular, organ-system and whole body level and of factors that affect zinc bioavailability; and (8) potential strategies for the prevention and management of human zinc deficiency. This review concludes with an emphasis on the immediate need for expanded research in directions that have become increasingly well demarcated and impelling as a result of recent progress, which is summarized in this overview.

Outcomes from a school-based nutrition education program alternating special resource teachers and classroom teachers.

This study modified a successful nutrition program to improve its transferability and potential for institutionalization. Specific aims were to determine: 1) if 16 nutrition lessons taught alternately by special resource teachers (SRT) and classroom teachers, could produce outcomes equivalent to 24 SRT lessons; and 2) teachers' reactions to the program. The quasi-experimental design used classrooms (19 treatment and 19 comparison) in matched schools. Surveys and plate waste measured children's outcomes, and classroom teachers were observed and interviewed. Treatment students showed greater knowledge and self-efficacy scores and consumed 0.36 more servings of fruits and vegetables at lunch. Behavioral differences between groups were greater when SRTs provided all instruction. Teachers supported the program and anticipated teaching more nutrition on their own, but noted serious structural barriers. Findings support the need for long-term contact to induce behavior change and the advantage of using teachers specifically trained in nutrition and experiential education.

Clinical conditions altering copper metabolism in humans.

Overt copper deficiency is not believed to be a widespread public health concern for most population groups. However, a variety of case studies suggest that under certain circumstances, clinical conditions may predispose individuals to the risk of copper deficiency or copper excess. Acquired copper deficiency has been documented in conditions predisposing to inadequate copper intakes, in prematurity, in malabsorption syndromes, and in conditions predisposing to excessive copper losses. In contrast, increases in copper concentrations have been reported in response to stress, inflammation, and infection; in Parkinson disease and diabetes mellitus; and in conditions involving an obstruction to bile flow.

Neural tube defects and serum zinc.

OBJECTIVE: To investigate the relationship of zinc in the causation of neural tube defects and so explore the possible role as a cause of these defects. DESIGN: Stored serum samples collected as part of the Medical Research Council's multicentre randomised trial section of vitamin supplementation in the prevention of neural tube defects were retrieved in respect of women who had had an affected pregnancy together with four matched unaffected controls per case. One control was selected from each of the four randomisation groups: 1. no extra vitamins; 2. folic acid supplementation alone; 3. folic acid and other vitamin supplementation; and 4. other vitamin supplementation, such that it was matched with an NTD case by study centre, maternal age (the year of birth differed at most by one year) and duration of storage of the serum sample (in most instances to within the same year). SETTING: A prospective case-control study using serum samples stored at -40 degrees C. The serum samples were collected from women at entry to the trial, immediately before the women became pregnant and at about 12 weeks of pregnancy. SUBJECTS: Twenty-seven women with a pregnancy associated with a neural tube defect and 108 matched controls with unaffected pregnancies. RESULTS: There was no association between serum zinc levels and neural tube defects; the mean values in microgram/dl were: 82 and 85 in cases and controls, respectively, at entry to the study; 86 and 87 micrograms/dl just before pregnancy; and 76 and 80 micrograms/dl in the first trimester of pregnancy. Folic acid supplementation did not have an effect on serum zinc levels. CONCLUSION: Within the range of serum zinc levels observed among women in our study, serum zinc is not a cause of neural tube defects, and periconceptional folic acid supplements do not compromise the zinc status of the mother or the embryo with respect to zinc intake.

Zinc status in children and young adults with sickle cell disease.

Previous studies have suggested an association of zinc deficiency and short stature in some children and adults with sickle cell disease (SCD). As a result, zinc supplementation has been recommended for these patients. The mechanism for zinc deficiency in certain patients with SCD is unknown, although renal loss of zinc has been suggested as a contributing factor. The zinc status of 29 subjects with SCD and 18 black controls was studied. No evidence of zinc deficiency in our population with SCD was found when plasma and cellular zinc levels were measured. Likewise, levels of two zinc-dependent enzymes, alkaline phosphatase and delta-aminolevulinic acid dehydratase, were normal in these subjects with SCD. Although adolescent subjects with SCD tended to be shorter than control subjects, there was no correlation between the height-forage z score and plasma zinc levels (r = -.31). It was concluded that zinc deficiency was not present in our population with SCD, and that there was no correlation between plasma zinc levels and the height-for-age z score in growing adolescent patients with SCD. These findings suggested that zinc supplementation may not be necessary in all patients with SCD.