Breastfeeding, maternal smoking and lower respiratory tract infections.

The objective of the study was to assess the relationship between breastfeeding and lower respiratory tract infections (LRTIs) during the first year of life, with special reference to maternal smoking. A cohort of 3,754 children born in 1992-1993 in the City of Oslo, Norway was recruited and data were collected at birth, 6 and 12 months of age. Complete information was obtained from 3,238 children (follow-up rate 86%). The main outcome was an episode of a LRTI, such as pneumonia, bronchitis or bronchiolitis, based on a self-administered questionnaire addressed to parents when the child was 6 and 12 months old. The outcome was specified as physician-diagnosed. In logistic regression analysis adjusting for confounding, maternal smoking increased the risk of LRTIs in children breastfed for 0-6 months (odds ratio (AOR) 1.7; 95% confidence interval (95% CI) 1.2-2.4), but not essentially when the child was breastfed for more than 6 months (AOR 1.1; 95% CI 0.7-1.6). Short-term breastfeeding (0-6 months) and no maternal smoking was related to an adjusted AOR of LRTIs of 1.3 (95% CI 1.0-1.7), and short-term breastfeeding combined with maternal smoking was related to an adjusted AOR of 2.2 (95% CI 1.6-3.1), as compared with long-term breastfeeding and no maternal smoking. The present study indicates a protective effect of long-term breastfeeding on the risk of lower respiratory tract infection during the first year of life. The results suggest that the protective effect is strongest in children exposed to environmental tobacco smoke.