Does breast-feeding influence intelligence quotients at 9 and 10 years of age?

The effect of breast-feeding on intellectual development remains controversial. We explored this relationship in a high socioeconomic population in which breast feeding was supplemented with soy containing formulas at some time during the first year of life. As part of the 1988 National Institute of Child Health and Human Development school-based survey of two metropolitan Washington, D.C. counties to identify children in the 1978 to 1979 birth cohort who had been exposed to the chloride deficient formulas Neo-Mull-Soy and Cho-Free during infancy, information on breast-feeding was also obtained on children exposed to the chloride-deficient formulas and a group of control children exposed to other soy formulas. Because no differences in intellectual development were observed between the two groups, they were combined and the effect of breast-feeding on intellectual development at 9 and 10 years was assessed. There were 176 infants that received no breast-feeding and 342 who were breast-fed. The median duration of breast feeding was 124 days (interquartile range, 42-248 days). There were no differences in birth weight, gender or race between the infants who were breast-fed and those who were not. The mean Weschler Intelligence Scale-Revised Full Scale IQ was 122 among those breast-fed compared to 118 among those that were not (P = 0.0008). However, following adjustment by Linear regression for maternal education, paternal education and annual income the adjusted mean full scale IQ was 111 among the breast-fed and 110 among the non-breast-fed (P = 0.23). Further analyses limited to those exclusively breast-fed for the first 60 days failed to demonstrate any significant relationship between breast-feeding and IQ. (C) 1998 Elsevier Science Ireland Ltd.