Breastfeeding effects on intelligence quotient in 4- and 11-year-old children.

OBJECTIVE A study of preterm children found an IQ advantage among those who were breastfed as infants after controlling for maternal social class and educational status. However, this advantage needs to be examined in light of other maternal characteristics, such as maternal IQ and parenting skills, which were not measured in that study and which have been found to be related to breastfeeding. METHODOLOGY IQ was assessed in 323 children at 4 years of age on the McCarthy Scales of Children's Abilities and the Peabody Picture Vocabulary Test-Revised and in 280 children on the Wechsler Intelligence Test for Children-Revised at 11 years of age. RESULTS Children who were breastfed in infancy had significantly higher scores on IQ tests at both ages, even after adjusting for social class and education, confirming the earlier findings and extending them to a predominantly full-term sample. However, the effect of breastfeeding was no longer significant after adjusting for maternal IQ assessed on the Peabody Picture Vocabulary Test-Revised and for parenting skills assessed on the Home Observation for Measurement of the Environment. Significant relations between breastfeeding and Woodcock Reading Achievement scores at 11 years were also reduced to nonsignificant levels after the inclusion of maternal IQ and the Home Observation for Measurement of the Environment. CONCLUSIONS These findings suggest that the observed advantage of breastfeeding on IQ is related to genetic and socioenvironmental factors rather than to the nutritional benefits of breastfeeding on neurodevelopment. They should not be interpreted as detracting from the medical benefits associated with breastfeeding.