New insights about iron bioavailability inhibition by zinc

Objective We measured the effects of lower and higher doses of zinc (Zn) given as an aqueous solution on the bioavailability of iron (Fe). Methods Fourteen healthy subjects received a solution with 0.5 mg of elemental Fe as ferrous sulfate given alone or with 0.59 mg of Zn as zinc sulfate (molar ratio Zn:Fe 1:1). Fourteen days after they received a second solution with 10 mg of Fe given alone or with 11.71 mg of Zn (molar ratio Zn:Fe 1:1). Iron bioavailability was assessed by erythrocyte incorporation of iron radioisotopes 55Fe and 59Fe. Results No significant effect of Zn on Fe bioavailability was observed at lower doses; however, at higher doses Fe bioavailability was inhibited by 56% (P < 0.001, repeated measures analysis of variance). Conclusion The inhibitory effect of Zn on Fe bioavailability depends on the total amount of both minerals present in the intestinal lumen. This fact should be considered when designing a supplementation program if Fe and Zn are to be provided together.