Factors modifying the effect of breastfeeding on the frequency of respiratory symptoms in infancy

The aim of this study is to explore possible factors modifying the effect of breastfeeding on the risk for respiratory symptoms in the first year of life. A subset of 407 children from the prospective Bern-Basel Infant Lung Development (BILD) cohort provided the weekly information about the breastfeeding status, and incidence and severity of respiratory symptoms during the first year of the life. A generalized additive mixed model (GAMM) with quasi Poisson distribution was used to assess a potential impact of breastfeeding duration on the development of respiratory symptoms in infancy. The multivariable longitudinal analysis adjusting for known confounders showed that the age modified the effect of breastfeeding on respiratory morbidity (p value for interaction <0.001). The protective effect of breastfeeding was dominantly observed in the first six months of life. The effect of N02-air pollution levels during pregnancy on night respiratory symptoms in the offspring was borderline significantly modified by the breastfeeding in a positive manner (p (interaction) =0.08). There was no interaction effect between breastfeeding and maternal smoking during the pregnancy. Additionally, we observed an age-dependent effect of maternal smoking during pregnancy on the frequency of respiratory symptoms in infancy (p value for interaction <0.001). In conclusion, the breastfeeding effect on respiratory symptoms in infancy depends on age and has a protective effect in the first six months of life. There is no combined effect of breastfeeding and maternal smoking.