Fine Particulate Matter (PM2.5) and the Risk of Stroke in the REGARDS Cohort

Background: Ambient particulate matter has been shown to be associated with declining human health, although the association between fine particulate matter (PM2.5) and stroke is uncertain. Methods: We utilized satellite-derived measures of PM2.5 to examine the association between exposure and stroke in the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. We used a time-stratified case-crossover design, with exposure lags of 1 day, 2 days, and 3 days. We examined all strokes, as well as ischemic and hemorrhagic strokes separately. Results: Among 30,239 participants in the REGARDS study, 746 incident events were observed: 72 hemorrhagic, 617 ischemic, and 57 of unknown type. Participants exposed to higher levels of PM2.5 more often resided in urban areas compared to rural, and in the southeastern United States. After adjustment for temperature and relative humidity, no association was observed between PM2.5 exposure and stroke, regardless of the lag (1-day lag OR = .99, 95% CI: .83-1.19; 2-day lag OR = .95, 95% CI: .80-1.14; 3-day lag OR = .95, 95% CI = .79-1.13). Similar results were observed for the stroke subtypes. Conclusions: In this large cohort of African Americans and whites, no association was observed between PM2.5 and stroke. The ability to examine this association with a large number of outcomes and by stroke subtype helps fill a gap in the literature examining the association between PM2.5 and stroke. (C) 2017 National Stroke Association. Published by Elsevier Inc. All rights reserved.