Iron supplementation affects growth and morbidity of breast-fed infants: results of a randomized trial in Sweden and Honduras

Iron supplements are often prescribed during infancy but their benefits and risks have not been well documented. We examined whether iron supplements affect growth or morbidity of breast-fed infants. Full-term infants in Sweden (n = 101) and Honduras (n = 131) were randomly assigned to three groups at 4 mo of age: 1) placebo from 4 to 9 mo; 2) placebo from 4 to 6 mo and iron supplements 1 mg/(kg. d)] from 6 to 9 mo; or 3) iron supplements from 4 to 9 mo. All infants were exclusively or nearly exclusively breast-fed to 6 mo and continued to be breast-fed to at least 9 mo. Growth was measured monthly and morbidity data were collected every 2 wk. Among the Swedish infants, gains in length and head circumference were significantly lower in those who received iron than in those given placebo from 4 to 9 mo. The same effect on length was seen in Honduras, but only at 4-6 mo among those with initial hemoglobin (Hb) > or =110 g/L. There was no significant main effect of iron supplementation on morbidity, nor any significant interaction between iron supplementation and site, but for diarrhea (with both sites combined), there was an interaction between iron supplementation and initial Hb. Among infants with Hb < 110 g/L at 4 mo, diarrhea was less common among those given iron than in those given placebo from 4-9 mo, whereas the opposite was true among those with Hb > or = 110 g/L (P < 0.05). We conclude that routine iron supplementation of breast-fed infants may benefit those with low Hb but may present risks for those with normal Hb.