Analysis of long- and medium-term particulate matter exposures and stroke in the US-based Health Professionals Follow-up Study

Purpose: Stroke is a leading cause of mortality worldwide, and air pollution is the third largest contributor to global stroke burden. Existing studies investigating the association between long-term exposure to particulate matter (PM) and stroke incidence have been mixed and very little is known about the associations with medium-term exposures. Therefore, we wanted to evaluate these associations in an cohort of male health professionals. Methods: We assessed the association of PM exposures in the previous 1 and 12 months with incident total, ischemic, and hemorrhagic stroke in 49,603 men in the prospective US-based Health Professionals' Follow-up Study 1988-2007. We used spatiotemporal prediction models to estimate monthly PM less than 10 (PM10) and less than 2.5 (PM2.5), and PM2.5-10 at all mailing addresses. We used time-varying Cox proportional hazards models adjusted for potential confounders based on previous literature to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for each 10-μg/m3 increase in exposure in the preceding 1 and 12 months. We explored possible effect modification by age, obesity, smoking, aspirin use, diet quality, physical activity, diabetes, and Census region. Results: We observed 1,467 cases of incident stroke. Average levels of 12-month PM10, PM2.5-10, and PM2.5 were 20.7, 8.4, and 12.3 μg/m3, respectively. In multivariable adjusted models, we did not observe consistent associations between PM and overall or ischemic stroke. There was a suggestion of increased risk of hemorrhagic stroke (12-month PM10 multivariable HR: 1.13 [0.86, 1.48]; PM2.5-10: 1.12 [0.78, 1.62]; PM2.5:1.17 [0.76, 1.81], all per 10 μg/m3). There was little evidence of effect modification. Conclusions: We observed only weak evidence of an association between long-term exposure to PM and risks of overall incident stroke. There was a suggestion of increasing hemorrhagic stroke risk.