Beneficial effects of BF on child morbi-mortality are well known, but the effects on infant development are still controversial. A prospective cohort study was carried out with 709 healthy low socioeconomic Chilean 4-mo-old infants, with follow-up until 12 mo. All infants were born at term weighing> 3.0 kg and were without acute or chronic illness. 100% were initially breastfed -- the norm in the community. Age at first bottle feeding and last breast feeding were determined by means of weekly home visits and monthly clinic visits. Longer BF before the introduction of any other milk feeding was associated with higher Bayley mental scores (MDI) at 12 mo (p <.05). This association remained statistically significant (p <.05) after control for environmental/family factors, such as sex, HOME score, mother's IQ, and socioeconomic status. This study shows that longer BF before the introduction of milk or formula is associated with higher mental development test scores in a developing country, an effect that has been previously reported in industrialized societies. The characteristics of this sample (100% initiation of BF and uniformly lower socioeconomic status) support the hypothesis that breast milk and/or the interactional process of nursing hypothesis contribute to better developmental outcome. Funded by NICHD and FONDECYT - Chile; milk and formula donated by Ross Laboratories. Table
