Inter-individual Variations in Zinc Requirements and Recommended Nutrient Intakes

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

36. FAO/WHO/UNU. 1985. Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series 724. Geneva, World Health Organization.

6. Milne, D.B., Canfield, W.K., Gallagher, S.K., Hunt, J.R. & Klevay, L.M. 1987. Ethanol metabolism in postmenopausal women fed a diet marginal in zinc. Am. J. Clin. Nutr., 46: 688-93.

7. Baer, M.J. & King, J.C. 1984. Tissue zinc levels and zinc excretion during experimental zinc depletion in young men. Am. J. Clin. Nutr., 39: 556-70.

8. Hess, F.M., King, J.C. & Margen, S. 1977. Zinc excretion in young women on low zinc intakes and oral contraceptive agents. J. Nutr., 107: 1610-20.

9. Milne, D.B., Canfield, W.K., Mahalko, J.R. & Sandstead, H.H. 1983. Effect of dietary zinc on whole body surface loss of zinc: impact on estimation of zinc retention by balance method. Am. J. Clin. Nutr., 38: 181-6.

10. Johnson, P.E., Hunt, C.D., Milne, D.B. & Mullen, L.K. 1993. Homeostatic control of zinc metabolism in men: zinc excretion and balance in men fed diets low in zinc. Am. J. Clin. Nutr., 57: 557-565.

The studies (6-10) used to estimate the average physiologic requirements with the factorial technique have considered a relatively small number of subjects and do not allow any estimate of inter-individual variations in obligatory losses of zinc at different intakes.

36. FAO/WHO/UNU. 1985. Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series 724. Geneva, World Health Organization.

Because zinc requirements are related to tissue turnover rate and growth, it is reasonable to assume that variations in physiologic zinc requirements are of the same magnitude as variations in protein requirements (36) and that the same figure (12.5 percent) for the inter-individual coefficient of variation (CV) could be adopted.

However, the estimates of dietary zinc requirements involve an estimate of absorption. Consequently, variations in absorptive efficiency, not relevant in relation to estimates of protein requirements, may have to be taken into account in the estimates of the total inter-individual variation in zinc requirements. Systematic studies of the inter-individual variations in zinc absorption under different conditions are few. In small groups of healthy well-nourished subjects, the reported variations in zinc absorption from a defined meal or diet are of the order of 20–40 percent and seem to be independent of age, sex, or diet characteristics.

19. Sian, L., Mingyan, X., Miller, L.V., Tong, L., Krebs, N.F. & Hambidge, K.M. 1996. Zinc absorption and intestinal losses of endogenous zinc in young Chinese women with marginal zinc intakes. Am. J. Clin. Nutr., 63: 348-53.

20. Sandström, B. 1989. Dietary pattern and zinc supply. In: Zinc in Human biology. Mills C.F. ed. p. 350-363. Devon , U.K., Springer-Verlag.

23. Knudsen, E., Jensen, M., Solgaard, P., Sørensen, S.S. & Sandström, B. 1995. Zinc absorption estimated by fecal monitoring of zinc stable isotopes validated by comparison with whole-body retention of zinc radioisotopes in Humans. J. Nutr., 125: 1274-1282.

27. Sandström, B. & Sandberg, A.S. 1992. Inhibitory effects of isolated inositol phosphates on zinc absorption in Humans. J Trace Elem Electrolyte Health Dis., 6: 99-103.

How much these variations, besides being attributable to methodologic imprecision, reflect variations in physiologic requirement, effects of preceding zinc intake, etc. is not known. From the available data from zinc absorption studies (19, 20, 23-27) it is tentatively suggested that the variation in dietary zinc requirements, which covers variation inrequirement for absorbed zinc (i.e., variations in metabolism and turnover rate of zinc) and variation in absorptive efficiency, corresponds to a CV of 25 percent. The recommended nutrient intakes derived from the estimates of average individual dietary requirements(Table 55) with the addition of 50 percent (2 standard deviations) are given in Table 56.