Health & body · 1987
Can high-dose zinc supplements reduce calcium absorption when calcium intake is low?
Yes. In adult males consuming an average of 230 mg of calcium daily, calcium absorption was 39.3% during high-dose zinc supplementation versus 61% in the control study; at a normal calcium intake of 800 mg/day, high zinc intake had no significant effect.
Details
Pharmacologic doses of zinc are widely used in zinc supplements. Because calcium and zinc may compete for common absorption sites, researchers studied the effect of a pharmacologic dose of zinc on intestinal calcium absorption in adult males.
The supplementation study compared normal and high zinc intake under both low and normal calcium intake conditions. Analyzed dietary zinc intake in the control studies was normal, averaging 14.6 mg/day. In the high zinc study, 140 mg of zinc as the sulfate was added daily for periods ranging from 17 to 71 days. Low calcium intake averaged 230 mg/day, while normal calcium intake was 800 mg/day.
During normal and high zinc intake, calcium absorption was measured using an oral tracer dose of Ca47, with measurements of plasma levels and urinary and fecal excretion of Ca47.
Under low calcium intake, intestinal calcium absorption was significantly lower during zinc supplementation than in the control study: 39.3% versus 61%, respectively (p < 0.001). At a normal calcium intake of 800 mg/day, however, high zinc intake had no significant effect on intestinal calcium absorption.
The researchers concluded that high zinc intake decreased intestinal calcium absorption during low calcium intake, but not during normal calcium intake.
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