A critical evaluation of the evidence on the association between type of infant feeding and cognitive development

This paper presents a critical evaluation of 24 studies on the association between type of infant feeding and cognitive development published over the past 20 years. Validity and generalisability of study findings were assess ed according to three methodological standards: clearly defined outcome, sp ecification of partial vs. exclusive breast feeding and control of confound ing. Only six of the 24 investigations met all three standards. The most fr equent study flaw was failure to distinguish between partial and exclusive breast feeding. Studies which made this distinction found larger IQ advanta ges to breast-fed, infants than studies that did not. Four of the six studi es meeting all three standards found an advantage in cognitive development to breast-fed infants of the order of two to five IQ points for term infant s and eight points for low birthweight infants. We conclude that the questi on of whether breast feeding and formula feeding have differential effects on cognitive development has not yet been comprehensively answered. Researc h to date provides only an indication of the effect of relatively brief dur ations of partial breast feeding and even briefer durations of exclusive br east feeding. Future studies should measure breast feeding as a continuous dose-type variable, examine longer durations of breast feeding and control for a full range of confounders using techniques that deal appropriately wi th multicollinearity.