Breastfeeding history and childhood allergic status in a prospective birth cohort

Background: Breastfeeding provides the best possible nutrition for newborns, but its role in the development of allergies is complex. Objective: To examine the relationship between breastfeeding and early childhood skin sensitization. Methods: In a birth cohort of 405 children from the Childhood Allergy Study, we used maternal report to classify children's duration of breastfeeding and whether they were breastfed only, formula fed only, or both. We examined the relationships between this information and childhood allergies as determined by skin prick testing for inhalant allergens at age 6 to 7 years. Results: There was no association between duration of breastfeeding and risk of allergic sensitization. Overall, children who were breastfed only were 50% more likely to have allergic sensitization than those fed formula only (relative risk [RR], 1.5; 95% confidence interval [CI], 1.1-2.1). Although the estimates are imprecise, this RR was higher for children born to mothers reporting a history of allergy (RR, 1.8; 95% CI, 1.0-3.0) than for those born to mothers with no allergic history (RR, 1.3; 95% CI, 0.9-2.1), for children in households without (RR, 1.6; 95% CI, 1.1-2.2) vs with (RR, 1.0; 95% CI, 0.3-4.0) multiple pets, and for those with an older sibling (RR, 2.0; 95% CI, 1.2-3.3) vs firstborns (RR, 1.3; 95% CI, 0.8-2.1). Conclusions: Breastfeeding without formula supplementation may be associated with an increased risk of childhood allergies. However, this association may vary with birth order, exposure to household pets, and maternal allergic history.