Ambient Air Pollution Exposures and Risk of Parkinson Disease

BACKGROUND: Few epidemiologic studies have evaluated the effects of air pollution on the risk of Parkinson disease (PD). OBJECTIVE: We investigated the associations of long-term residential concentrations of ambient particulate matter (PM) < 10 mu m in diameter (PM10) and < 2.5 mu m in diameter (PM2.5) and nitrogen dioxide (NO2) in relation to PD risk. METHODS: Our nested case-control analysis included 1,556 self-reported physician-diagnosed PD cases identified between 1995 and 2006 and 3,313 controls frequency-matched on age, sex, and race. We geocoded home addresses reported in 1995-1996 and estimated the average ambient concentrations of PM10, PM2.5, and NO2 using a national fine-scale geostatistical model incorporating roadway information and other geographic covariates. Air pollutant exposures were analyzed as both quintiles and continuous variables, adjusting for matching variables and potential confounders. RESULTS: We observed no statistically significant overall association between PM or NO2 exposures and PD risk. However, in preplanned subgroup analyses, a higher risk of PD was associated with higher exposure to PM10 (ORQ5 (vs. Q1) = 1.65; 95% CI: 1.11, 2.45; p-trend = 0.02) among women, and with higher exposure to PM2.5 (ORQ5 (vs. Q1) = 1.29; 95% CI: 0.94, 1.76; p-trend = 0.04) among never smokers. In post hoc analyses among female never smokers, both PM2.5 (ORQ5 (vs. Q1) = 1.79; 95% CI: 1.01, 3.17; p-trend = 0.05) and PM10 (ORQ5 (vs. Q1) = 2.34; 95% CI: 1.29, 4.26; p-trend = 0.01) showed positive associations with PD risk. Analyses based on continuous exposure variables generally showed similar but nonsignificant associations. CONCLUSIONS: Overall, we found limited evidence for an association between exposures to ambient PM10, PM2.5, or NO2 and PD risk. The suggestive evidence that exposures to PM2.5 and PM10 may increase PD risk among female never smokers warrants further investigation.