Breastfeeding decreases the effect of ambient air pollution on respiratory symptoms and illness in Chinese children: The 25 Districts Chinese Study (DCS)

Background: Evidence indicates that exposure to ambient air pollution and breastfeeding are both important factors for respiratory symptoms and illness in children. However, few studies have examined the potential interaction of air pollution and breastfeeding on respiratory health. Objectives: Evaluate whether breastfeeding modifies the effects of air pollution exposure on children's respiratory health. Methods: 31,049 children aged 2 to 14 years were selected from 25 elementary schools and 50 kindergartens within 25 districts of seven cities in Northeast China. Parents of selected children completed questionnaires characterizing the histories of respiratory illness, associated risk factors, and means of feeding. Monitoring stations in each of the 25 study districts estimated local average annual exposure to particles with an aerodynamic diameter ≤10 µm (PM10); sulfur dioxide (SO2); nitrogen dioxides (NO2); and ozone (O3). Results: Statistically significant effects were observed for the interactions between air pollution and breastfeeding on children's respiratory symptoms and illness. Compared to children who had been breastfed for at least 3 months, children who were not breastfed exhibited consistently more respiratory symptoms and illnesses. Odds ratios (ORs) ranged from 1.17 per 21 µg/m3 for SO2 [95% confidence interval (CI), 1.04-1.32] to 1.44 per 20 µg/m3 for NO2 (95% CI, 1.24–1.66). Interactions for chronic cough and phlegm among kindergarten children were particularly observed, as well as wheezing among elementary school children. Breastfed children exhibited smaller effects. Conclusion: Findings indicate that breastfeeding decreases the detrimental effects of ambient air pollution on respiratory symptoms and illness among participating children.