Breastfeeding and Lung Function at School Age: Does Maternal Asthma Modify the Effect?

Rationale The evidence for an effect of breastfeeding on lung function is conflicting, in particular whether the effect is modified by maternal asthma. Objectives To explore the association between breastfeeding and school-age lung function. Methods In the Leicestershire Cohort Studies we assessed duration of breastfeeding (not breastfed, ≤3 months, 4–6 months, and >6 months), other exposures, and respiratory symptoms by repeated questionnaires. Post-bronchodilator FVC, FEV1, peak expiratory flow (PEF), forced midexpiratory flow (FEF50), and skin prick tests were measured at age 12 years. We performed multivariable linear regression and tested potential causal pathways (N = 1,458). Measurements and Main Results In the entire sample, FEF50 was higher by 130 and 164 ml in children breastfed for 4 to 6 months and longer than 6 months, respectively, compared with those not breastfed (P = 0.048 and 0.041), with larger effects if the mother had asthma. FVC and FEV1 were associated with breastfeeding only in children of mothers with asthma (P for interaction, 0.018 and 0.008): FVC was increased by 123 and 164 ml for those breastfed 4 to 6 months or longer than 6 months, respectively (P = 0.177 and 0.040) and FEV1 was increased by 148 and 167 ml, respectively (P = 0.050 and 0.016). Results were unchanged after adjustment for respiratory infections in infancy and asthma and atopy in the child. Conclusions In this cohort, breastfeeding for more than 4 months was associated with increased FEF50 and, in children of mothers with asthma, with increased FEV1 and FVC. It seems that the effect is not mediated via avoidance of early infections or atopy but rather through a direct effect on lung growth.