Upper Limits of Zinc Intake

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

Only a few occurrences of acute zinc poisoning have been reported. The toxicity signs are nausea, vomiting, diarrhoea, fever, and lethargy and have been observed after ingestion of 4-8 g (60-120 mmol) zinc. Long-term zinc intakes higher than the requirements could, however, interact with the metabolism of other trace elements. Copper seems to be especially sensitive to high zinc doses.

37. Fischer, P.W.F., Giroux, A. & L'Abbé, M.R. 1984. Effect of zinc supplementation on copper status in adult man. Am. J. Clin. Nutr., 40: 743-6.

38. Yadrick, M.K., Kenney, M.A. & Winterfeldt, E.A. 1989. Iron, copper, and zinc status: response to supplementation with zinc or zinc and iron in adult females. Am. J. Clin. Nutr., 49: 145-50.

39. Patterson, W.P., Winkelmann, M. & Perry, M.C. 1985. Zinc-induced copper deficiency: megamineral sideroblastic anemia. Ann. Internal Med.. 103: 385-6.

40. Porter, K.G., McMaster, D., Elmes, M.E. & Love, A.H.G. 1977. Anemia and low serum-copper during zinc therapy. Lancet, II: 774.

41. Hooper, P.L., Visconti, L., Garry, P.J. & Johnson, G.E. 1980. Zinc lowers high-density lipoprotein-cholesterol levels. JAMA, 244: 1960-2.

42. Chandra, R.K. 1984. Excessive intake of zinc impairs immune responses. JAMA, 252: 1443-6.

A zinc intake of 50 mg/day (760 μmol) affects copper status indexes, such as CuZn-superoxide dismutase in erythrocytes (37, 38). Low copper and ceruloplasmin levels and anaemia have been observed after higher zinc intakes 450-660 mg/day (6.9-10 mmol/day) (39, 40). Changes in serum lipid pattern and in immune response have also been observed in zinc supplementation studies (41, 42).

Because copper also has a central role in immune defence, these observations call for caution before large-scale zinc supplementation programmes are undertaken. Any positive effects of zinc supplementation on growth or infectious diseases could be disguised or counterbalanced by negative effects on copper related functions.

The upper level of zinc intake for an adult man is set at 45 mg/day (690 μmol/day) and extrapolated to other groups in relation to basal metabolic rate. For children this extrapolation means an upper limit of intake of 23–28 mg/day (350–430 μmol/day), which is close to what has been used in some of the zinc supplementation studies. Except for excessive intakes of some types of seafood, such intakes are unlikely to be attained with most diets. Adventitious zinc in water from contaminated wells and from galvanized cooking utensils could also lead to high zinc intakes.