Zinc Requirements

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

32. AO/IAEA/WHO. 1996. Trace elements in Human nutrition and health. Geneva, World Health Organization.

The lack of specific and sensitive indexes for zinc status limits the possibilities for evaluating zinc requirements from epidemiologic observations. In the FAO/IAEA/WHO 1996 report (32), zinc requirements were estimated by using the factorial technique (i.e., by adding the requirements for tissue growth, maintenance, metabolism, and endogenous losses).

5. Lukaski, H.C., Bolonchuk, W,W., Klevay, L.M., Milne, D.B. & Sandstead, H.H. 1984. Changes in plasma zinc content after exercise in men fed a low-zinc diet. Am. J. Physiol., 247: E88-93.

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.

33. Taylor, C.M., Bacon, J.R., Aggett, P.J. & Bremner, I. 1991. Homeostatic regulation of zinc absorption and endogenous losses in zinc-deprived men. Am. J. Clin. Nutr., 53: 755-63.

Experimental zinc repletion studies with low zinc intakes have clearly shown that the bodyhas a pronounced ability to adapt to different levels of zinc intakes by changing theendogenous zinc losses through the kidneys, intestine, and skin (5-9,33).

32. AO/IAEA/WHO. 1996. Trace elements in Human nutrition and health. Geneva, World Health Organization.

The normative requirement for absorbed zinc was defined as the obligatory loss during the early phase of zinc depletion before adaptive reductions in excretion take place and was set at 1.4 mg/day for men and 1.0 mg/day for women. To estimate the normative maintenance requirements for other age groups, the respective basal metabolic rates were used for extrapolation. 

In growing individuals the rate of accretion and zinc content of newly formed tissues were used to obtain the data required for tissue growth. Similarly, the retention of zinc during pregnancy and the zinc concentration in milk at different stages of lactation were used to estimate the physiologic requirements in pregnancy and lactation (32).

The translation of these estimates of absorbed zinc to requirements for dietary zinc involves several considerations. First, the nature of the diet (i.e., its content of promoters and inhibitors of zinc absorption) determines the fraction of the dietary zinc that is potentially absorbable. Second, the efficiency of absorption of potentially available zinc is inversely related to the content of zinc in the diet. 

The review of available data from experimental zinc absorption studies of single meals or total diets resulted in a division of diets into three categories – high, moderate, and low zinc bio-availability – as detailed in Table 54 (32). It was then discovered that the relationship between efficiency of absorption and zinc content differed for these diets (32). 

Algorithms were developed (32) and applied to the estimates of requirements for absorbed zinc to achieve a set of figures for the average individual dietary zinc requirements (Table 55). The fractional absorption figures applied for the three diet categories were 50 percent, 30 percent, and 15 percent, respectively. From these estimates and from the evaluation of data from dietary intake studies, mean population intakes were identified which were deemed sufficient to ensure a low prevalence of individuals at risk of inadequate zinc intake (32).

Infants, children, and adolescents

Endogenous losses of zinc in human-milk-fed infants were assumed to be 20 μg/kg/day(0.31μmol/kg/day) whereas 40 μg/kg/day (0.6 μmol/kg/day) was assumed for infants fed formula or weaning foods (32). 

For other age groups an average loss of 0.002 μmol/basal kJ(0.57 μg/basal kcal) was derived from the estimates in adults.

Estimated zinc increases for infant growth were set at 120 and 140 μg/kg/day (1.83–2.14 μmol/kg/day) for female and male infants, respectively, for the first 3 months (32). 

These values decrease to 33 μg/kg/day(0.50 μmol/kg/day) for ages 6–12 months. For ages 1–10 years the requirements for growth were based on the assumption that new tissue contains 30 μg/g (0.46 μmol zinc/g) (32). 

For adolescent growth, a zinc content of 23 μg/g (0.35 μmol/g) increase in body weight was assumed. Pubertal growth spurts increase physiologic zinc requirements substantially. Growth of adolescent males corresponds to an increase in body zinc requirement of about 0.5 mg/day(7.6 μmol/day) (32).

Pregnancy

32. AO/IAEA/WHO. 1996. Trace elements in Human nutrition and health. Geneva, World Health Organization.

34. Swanson, C.A. & King, J.C. 1987. Zinc and pregnancy outcome. Am. J. Clin. Nutr., 46:763-771.

The total amount of zinc retained during pregnancy has been estimated to be 1.5 mmol (100mg) (34). During the third trimester the physiologic requirement of zinc is approximately twice as high as that in women who are not pregnant (32).

Lactation

35. World Health Organization. 1998. Complementary feeding of young children in developing countries: a review of current scientific knowledge. Geneva, World Health Organization.

Zinc concentrations in human milk are high in early lactation, 2-3 mg/l (31-46 μmol/l) in thefirst month, and fall to 0.9 mg/l (14 μmol/l) after 3 months (35).

From data on maternal milk volume and zinc content, it was estimated that the daily output of zinc in milk during the first 3 months of lactation could amount to 1.4 mg/day (21.4 μmol/l), which would theoretically triple the physiologic zinc requirements in lactating women compared with non-lactating,non-pregnant women. In setting the estimated requirements for early lactation it was assumed that part of this requirement was covered by postnatal involution of the uterus and from skeletal resorption (32).

Elderly

Requirements for the elderly are estimated to be the same as those for other adults. A lower absorptive efficiency has been reported in the elderly, which could justify a higher dietary requirement. On the other hand, endogenous losses seem to be lower in the elderly. Because of the suggested role of zinc in infectious diseases, an optimal zinc status in the elderly could have a significant public health effect and is an area of zinc metabolism requiring further research.