HIGH DIETARY CALCIUM INTAKES REDUCE ZINC-ABSORPTION AND BALANCE IN HUMANS

Optimal calcium intakes of 37.5 mmol (1500 mg)/d have been proposed fo r elderly people. We investigated the effects of calcium supplementati on on zinc absorption and balance in 18 relatively healthy, postmenopa usal women aged 59-86 y. All subjects received a standardized basal di et of typical foods supplying 269 mu mol (17.6 mg) Zn/d and 22.2 mmol (890 mg) Ca/d during the 36-d study. In two of three experimental peri ods, an additional 11.7 mmol (468 mg) Ca/d as either milk or an inorga nic calcium phosphate supplement was provided. Net zinc absorption and zinc balance were significantly reduced by approximate to 2 mg/d duri ng both high-calcium treatments. In a second study, conducted in a sep arate group of men and women aged 21-69 y, a whole-gut lavage, zinc-ab sorption test was used to investigate the acute effect of a 15-mmol Ca CO3 (600 mg Ca) supplement, with and without extra zinc, on zinc absor ption from a single test meal supplying 111.7 mu mol (7.3 mg) Zn. Zinc absorption was reduced significantly by 50% when the calcium suppleme nt was given with the meal. Inclusion of an extra 119.3 mu mol (7.8 mg ) Zn as part of a calcium supplement offset the detrimental effect of calcium on zinc absorption. Our findings suggest that high-calcium die ts can reduce net zinc absorption and balance and may increase the zin c requirement in adult humans.