Efficacy of weekly compared with daily iron supplementation

A reduction in the frequency of iron supplement administration to once or twice weekly is being widely examined in developing countries on the assumption that the side effects of oral iron will decrease and that the reduction in administered iron will be offset by a lesser inhibition in absorption from iron taken on the previous day. We examined this premise by measuring iron absorption from 50 mg radiolabeled ferrous sulfate in 23 female volunteer subjects divided into two groups. In the first group, a labeled ferrous sulfate supplement was given with water, and in the second group it was given with a rice-based meal. In both groups, absorption was measured in a randomized fashion twice in each subject, once with daily and once with weekly supplementation. Those tested for daily supplementation were given an iron supplement daily for 6 d before testing whereas those tested for weekly supplementation were given no iron for 6 d before testing. When the labeled iron supplement was given with water only, absorption averaged 8.5% with daily and 9.8% with weekly administration compared with 2.3% and 2.6%, respectively, when given with food. The 13% lower absorption observed with daily administration in both groups was not statistically significant (P > 0.20). These results indicate that there is no significant absorptive advantage in giving iron less often than once daily.