L. John Horwood, MSc, BA, and David M. Fergusson, PhD
This study examines the associations between duration of breastfeeding and childhood cognitive ability and academic achievement over the period from 8 to 18 years using data collected during the course of an 18-year longitudinal study of a birth cohort of more than 1000 New Zealand children.
During the period from birth to age 1 year, information was collected on maternal breastfeeding practices. Over the period from 8 to 18 years, sample members were assessed on a range of measures of cognitive and academic outcomes including measures of child intelligence quotient; teacher ratings of school performance; standardized tests of reading comprehension, mathematics, and scholastic ability; pass rates in school leaving examinations; and leaving school without qualifications.
Increasing duration of breastfeeding was associated with consistent and statistically significant increases in 1) intelligence quotient assessed at ages 8 and 9 years; 2) reading comprehension, mathematical ability, and scholastic ability assessed during the period from 10 to 13 years; 3) teacher ratings of reading and mathematics assessed at 8 and 12 years; and 4) higher levels of attainment in school leaving examinations. Children who were breastfed for greater than or equal to 8 months had mean test scores that were between 0.35 and 0.59 SD units higher than children who were bottle-fed.
Mothers who elected to breastfeed tended to be older; better educated; from upper socioeconomic status families; were in a two-parent family; did not smoke during pregnancy; and experienced above average income and living standards. Additionally, rates of breastfeeding increased with increasing birth weight, and first-born children were more likely to be breastfed.
Regression adjustment for maternal and other factors associated with breastfeeding reduced the associations between breastfeeding and cognitive or educational outcomes. Nonetheless, in 10 of the 12 models, fitted duration of breastfeeding remained a significant predictor of later cognitive or educational outcomes. After adjustment for confounding factors, children who were breastfed for greater than 8 months had mean test scores that were between 0.11 and 0.30 SD units higher than those not breastfed.
It is concluded that breastfeeding is associated with small but detectable increases in child cognitive ability and educational achievement. These effects are 1) pervasive, being reflected in a range of measures including standardized tests, teacher ratings, and academic outcomes in high school; and 2) relatively long- lived, extending throughout childhood into young adult- hood.