Breast-feeding and cognitive development: a meta-analysis.

BACKGROUND Although the results of many clinical studies suggest that breast-fed children score higher on tests of cognitive function than do formula-fed children, some investigators have suggested that these differences are related to confounding covariables such as socioeconomic status or maternal education. OBJECTIVE Our objective was to conduct a meta-analysis of observed differences in cognitive development between breast-fed and formula-fed children. DESIGN In this meta-analysis we defined the effect estimate as the mean difference in cognitive function between breast-fed and formula-fed groups and calculated average effects using fixed-effects and random-effects models. RESULTS Of 20 studies meeting initial inclusion criteria, 11 studies controlled for >/=5 covariates and presented unadjusted and adjusted results. An unadjusted benefit of 5.32 (95% CI: 4.51, 6.14) points in cognitive function was observed for breast-fed compared with formula-fed children. After adjustment for covariates, the increment in cognitive function was 3.16 (95% CI: 2.35, 3.98) points. This adjusted difference was significant and homogeneous. Significantly higher levels of cognitive function were seen in breast-fed than in formula-fed children at 6-23 mo of age and these differences were stable across successive ages. Low-birth-weight infants showed larger differences (5.18 points; 95% CI: 3.59, 6.77) than did normal-birth-weight infants (2.66 points; 95% CI: 2.15, 3.17) suggesting that premature infants derive more benefits in cognitive development from breast milk than do full-term infants. Finally, the cognitive developmental benefits of breast-feeding increased with duration. CONCLUSION This meta-analysis indicated that, after adjustment for appropriate key cofactors, breast-feeding was associated with significantly higher scores for cognitive development than was formula feeding.