Abstract
Introduction: Epidemiological studies have revealed adverse associations between ambient fine particulate matter (PM 2.5 ; aerodynamic diameter < 2.5 μm) and cardiovascular diseases. Recently, there has been increased interest in investigating the association between long-term PM 2.5 exposure and hemorrhagic stroke (HS) and identifying the most susceptible subpopulations to the PM 2.5 exposure, if any. Hypothesis: We assessed the hypothesis that long-term cumulative averages of PM 2.5 exposure affect HS and its effect might be modified by risk factors. Methods: This study was based on a nationwide representative cohort of 1,025,340 participants, or 2% of the National Health Insurance Service enrollees in Korea (2002-2013). We analyzed the effects of PM 2.5 on time to first hospital diagnosis for HS for participants living in Seoul. A time-dependent Cox proportional hazards model was used with adjustments for age, sex, household income, insurance type, body mass index, smoking status, exercise, medical history, and family history. Annual cumulative mean PM 2.5 concentrations for 25 districts were used as the time-dependent variables. Subgroup analyses were performed to evaluate potential effect modification. Results: Cumulative PM 2.5 exposure was associated with HS events with a hazard ratio of 1.04 (95% confidence interval [CI]: 1.01-1.07) per 1 μg/m 3 elevation in PM 2.5 . Its adverse effects were modified by risk factors with greater effects observed among women (1.05 [1.01-1.09]) and subgroups with hypertension (1.06 [1.03-1.10]), without diabetes (1.05 [1.02-1.09]), or without family history of stroke (1.04 [1.01-1.07]). Conclusions: To our best knowledge, this is the first study to investigate the effect of cumulative averages of PM 2.5 exposure on time to first hospital diagnosis for HS. Cumulative PM 2.5 exposure might increase the risk of HS. Participants with hypertension, without diabetes or family history of stroke, or women were more susceptible to PM 2.5 exposure. Our findings show the first time that long-term cumulative PM 2.5 exposure could be crucial to cerebrovascular event and have public health implications.
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