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

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.

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 (PM_2.5), and PM_2.5-10 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.

We observed 1,467 cases of incident stroke. Average levels of 12-month PM₁₀, PM_2.5-10, and PM_2.5 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]; PM_2.5-10: 1.12 [0.78, 1.62]; PM_2.5:1.17 [0.76, 1.81], all per 10 µg/m³). There was little evidence of effect modification.

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.