Fine particulate matter exposure and incidence of stroke: A cohort study in Hong Kong

We aimed to assess the association of long-term residential exposure to fine particulate matter (PM) with aerodynamic diameter less than 2.5 μm (PM_2.5) with the incidence of stroke and its major subtypes.

We ascertained the first occurrence of emergency hospital admission for stroke in a Hong Kong Chinese cohort of 66,820 older people (65+ years) who enrolled during 1998-2001 (baseline) and were followed up to December 31, 2010. High-resolution (1 × 1 km) yearly mean concentrations of PM_2.5 were predicted from local monitoring data and US National Aeronautics and Space Administration satellite data using linear regression. Baseline residential PM_2.5 exposure was used as a proxy for long-term exposure. We used Cox proportional hazards to evaluate the risk of incident stroke associated with PM_2.5 exposure adjusted for potential confounders, including individual and neighborhood factors.

Over a mean follow-up of 9.4 years, we ascertained 6,733 cases of incident stroke, of which 3,526 (52.4%) were ischemic and 1,175 (17.5%) were hemorrhagic. The hazard ratio for every 10 μg/m³ higher PM_2.5 concentration was statistically significant at 1.21 (95% confidence interval [CI] 1.04-1.41) for ischemic and non-statistically significant at 0.90 (95% CI 0.70-1.17) for hemorrhagic stroke in fully adjusted model 3. The estimates for ischemic stroke were higher in older participants (>70 years), less educated participants, and in men for current smokers.

Long-term PM_2.5 exposure was associated with higher risk of incident ischemic stroke, but the association with incident hemorrhagic stroke was less clear.