25 Inhibition of Iron Absorption by Zinc

Abstract

Background. Iron and zinc deficiencies are the most common nutritional deficiencies worldwide. Supplementation is one of the strategies utilized to prevent these deficiencies. Because divalent cations share the same enterocyte transporter, there is an increasing concern about potential negative interactions between these two microminerals. Objective. To measure the dose-response effect of zinc, given in a solution, on iron absorption. Methods. Twenty-two healthy adult women were selected to participate in two iron absorption studies. One group of women received a solution with 0.5 mg of elemental iron, as ferrous sulfate, given alone and with zinc, as zinc sulfate, in molar ratios Zn:Fe 0.5:1, 1:1, 2:1; the other group received a solution with 0.5 mg of iron given alone and with zinc in molar ratios Zn: Fe 5:1, 10:1 and 20:1. The double radioisotopic technique was used to measure iron absorption. Iron absorption values were referred to the iron absorption of the solution without zinc. Results. Both groups had comparable iron nutrition status. No significant effect of zinc on iron absorption occurred at Zn:Fe molar ratios up to 2:1. Among 5:1, 10:1 and 20:1 molar ratios, a dose dependent inhibitory effect on iron absorption was observed (28 to 40 % of iron absorption inhibition; ANOVA for repeated measures, F = 4.476, p = 0.01). Conclusion. Zn negative affects iron absorption at Zn: Fe molar ratio equal or higher to 5:1. Supported by Fondecyt grant 1040879.