Traffic-Related Air Pollution Exposure and Adult Asthma in the Sister Study

Thesis (Master's)--University of Washington, 2013Background: Previous epidemiologic research has suggested an association between air pollution exposure and adult incident asthma. However, there exists limited research specifically focusing on the effect of PM2.5 on asthma in adults. Aims: A prospective analysis was performed to estimate the association between ambient air pollution exposures (NO2, PM2.5) and incident asthma and incident onset of respiratory symptoms. Methods: The Sister Study is a national population-based cohort (n=50,884) of sisters of women with diagnosed breast cancer. Participants were asked questions about medical conditions at enrollment and again at follow-up, an average of 2.9 years later. Participant exposures were year 2006 annual average ambient PM2.5 and NO2 concentrations estimated at participant baseline addresses using a national land-use regression kriging model. The primary outcome was incident self-reported doctor-diagnosed asthma at follow-up in individuals who were asthma-free at baseline. Secondary outcomes were new onset of wheeze or cough in individuals who did not report asthma, wheeze or cough at baseline. Logistic regression was used to assess the relationship between participant exposure and outcomes at follow-up. Models were adjusted for the following covariates based on a directed acyclic graph: age at baseline, race/ethnicity, educational attainment, BMI, occupational dust exposure, occupational vapor exposure, baseline smoking status, age first smoked, packs/day at baseline, smoking status between baseline and follow-up, childhood environmental tobacco smoke exposure, healthcare coverage, and dietary fiber consumption. Results: The Sister Study cohort interquartile ranges (IQR) of estimated PM2.5 and NO2 were 3.5 µg/m3 and 5.8 ppb respectively. The adjusted OR of incident asthma for PM2.5 was 1.20 (95% CI: 0.99-1.45, p=0.069) for an IQR difference in estimated PM2.5 exposure. The adjusted OR of onset wheeze for PM2.5 was 1.13 (95% CI: 1.02-1.25, p=0.015) for an IQR difference in PM2.5 exposure. PM2.5 was not significantly associated with cough or the combined outcome of cough and wheeze. NO2 was not significantly associated with the either incident asthma or onset of wheeze and/or cough. Conclusions: PM2.5 exposure may be a risk factor in the development of incident asthma or wheeze, the cardinal symptom of asthma, in adult women