Iron and zinc deficiencies are the most common nutritional deficiencies worldwide. Combined zinc and iron supplementation are one of the strategies used to prevent these deficiencies. Zinc has an inhibitory effect on iron absorption. The objective of the study was to determine the duration of the inhibitory effect of zinc on iron absorption. Fifteen healthy subjects were selected to participate in the study. Subjects received a water solution with 0.5 mg of elemental iron, as ferrous sulfate, given alone or with zinc (11.71 mg), as zinc sulfate, in a molar ratio 20:1 zinc to iron, provided simultaneously with iron or 30 and 60 minutes before iron administration. The double radioisotopic technique was used to measure iron absorption. An inhibitory effect of zinc on iron absorption was observed when both mineral were given simultaneously; however, this inhibitory effect was not observed when zinc was administered 30 or 60 minutes before (analysis of variance for repeated measures, F = 5.96, P < .002; Scheffé post hoc test, P< .006). In conclusion, zinc administration with iron in aqueous solution leads to the inhibition of iron bioavailability. However, this inhibitory effect lasts less than 30 minutes. The timing of this negative interaction should be considered for supplementation programs with both minerals. Read more.