New insights about iron bioavailability inhibition by zinc
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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.