True absorption and retention of supplemental iron is more efficient when iron is administered every three days rather than daily to iron-normal and iron-deficient rats.

Absorption of daily iron supplements is inefficient. Detailed absorption patterns of FeSO4 supplements simulating World Health Organization-recommended doses were studied in iron-deficient and iron-normal male Sprague-Dawley rats. For 12 d after weaning, the rats were fed a premeal containing < 20 (iron-deficient group) or 400 micrograms Fe (iron-normal group) twice daily followed by iron-free AIN-76 diet for 1 h. Then, both groups (iron-deficient and -normal) were divided in three groups, one continuing without change and two receiving 4000 micrograms of premeal Fe either daily or every 3 d to match intestinal mucosa renewal time. Food intake, growth, hemoglobin concentration and periodic 59Fe-labeled iron absorption and rate of loss were determined. Iron-deficient rats became anemic, and ate and grew less. Iron absorption was stable in normal (34.2%), deficient (89.7%) and normal, intermittently supplemented (9.5%) groups. Absorption decreased logarithmically in daily supplemented rats, whereas in iron-deficient, intermittently supplemented rats absorption decreased slowly and linearly. Rates of iron loss were significantly accelerated in daily supplemented rats. Thirteen-day total iron retention in intermittently supplemented normal and deficient rats was 62 and 86%, respectively, of that of daily supplemented rats. Iron supplementation timed to match mucosal renewal is more efficient.