Breast-feeding and the risk of bronchial asthma in childhood: A systematic review with meta-analysis of prospective studies

Background: The protective effect of breast-feeding on the development of childhood asthma remains a matter of controversy. We conducted a systematic review of prospective studies that evaluated the association between exclusive breast-feeding during the first 3 months after birth and asthma. Study design: We searched the 1966-1999 MEDLINE database and reviewed reference lists of relevant articles to identify 12 prospective studies that met pre-stated inclusion criteria. Methodological aspects of the studies, duration and exclusivity of breast-feeding, and outcomes were assessed. Effect estimates were abstracted by the investigators, using a standardized approach. Results: The summary odds ratio (OR) for the protective effect of breast-feeding was 0.70 (95% CI 0.60 to 0.81). The effect estimate was greater in studies of children with a family history of atopy (OR = 0.52) than in studies of a combined population (OR = 0.73). Conclusions: Exclusive breast-feeding during the first months after birth is associated with lower asthma rates during childhood. The effect, caused by immunomodulatory qualities of breast milk, avoidance of allergens, or a combination of these and other factors, strengthens the advantage of breast-feeding, especially if a family history of atopy is present.