It has been suggested that children that are exposed to a stressful environment at home have an increased susceptibility for air pollution-related asthma. The aim here was to investigate the association between air pollution exposure and asthma, and effect modification by mental health and by socio-economic status (as markers of a stressful environment). All individuals under 18 years of age in four Swedish counties during 2007 to 2010 (1.2 million people) were included. The outcome was defined as dispensing at least two asthma medications during follow up. We linked data on NO₂ from an empirical land use regression to data from national registers on outcome and potential confounders. Data was analyzed with logistic regression. There was an odds ratio (OR) of 1.02 (95% Confidence Interval (CI: 1.01-1.03) for asthma associated with a 10 µg·m-3 increase in NO₂. The association only seemed to be present in areas where NO₂ was higher than 15 µg·m-3 with an OR of 1.09 (95% CI: 1.07-1.12), and the association seemed stronger in children with parents with a high education, OR = 1.05 (95% CI: 1.02-1.09) and OR = 1.04 (95% CI: 1.01-1.07) in children to mothers and father with a high education, respectively. The association did not seem to depend on medication history of psychiatric disorders. There was weak evidence for the association between air pollution and asthma to be stronger in neighborhoods with higher education levels. In conclusion, air pollution was associated with dispensed asthma medications, especially in areas with comparatively higher levels of air pollution, and in children to parents with high education. We did not observe support for our hypothesis that stressors linked to socio-economy or mental health problems would increase susceptibility to the effects of air pollution on the development of asthma.
Keywords: air pollution; asthma; childhood asthma; mental health; socio-economy; stress.