Several studies have shown that IDA in infants is associated with lower developmental test scores, but this association is confounded by environmental disadvantages. A double-blind placebo-controlled preventive trial was undertaken in which 944 healthy Chilean 6-mo-old infants were randomly assigned to supplemental iron or no added iron (current feeding routine in Chile) until 12 months of age. All infants were born at term, BW > 3.0 kg, had no acute or chronic illness, had normal Hb levels at 6 mos, and almost all had been breast fed. Supplemented and unsupplemented groups were comparable in growth, family background, and Hb levels at study entry. At 12 mo, the supplemented group had less anemia (Hb < 110 g/L) and less iron deficiency(2 of 3 abnormal measures--FEP, MCV, ferritin), but, in contrast to a recent smaller preventive trial in Canada, did not show higher Bayley mental (MDI) or mo or (PDI) scores. There was > 90% power to detect a 3 point difference if present. The study suggests that factors other than IDA per se account for lower Bayley scores observed in iron-deficient anemic infants. Differences between this and other samples suggest such factors might be environmental disadvantage, no breast feeding, BW < 3 kg, IDA onset before 6 mo or after 12 mo or duration > 6 mo. Funded by NICHD; milk and formula donated by Ross Laboratories. Table

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