Associations of Outdoor Air Pollution With Hemorrhagic Stroke Mortality

OBJECTIVE: Evidence linking short-term exposure to outdoor air pollution with hemorrhagic stroke is inconsistent. METHODS: We evaluated the associations between outdoor air pollution and specific types of stroke in Tokyo, Japan, from April 2003 to December 2008. We obtained daily counts of stroke mortality (n = 41,440) and concentrations of nitrogen dioxide as well as particles less than 2.5 μm in diameter. Time-series analysis was employed. RESULTS: Although same-day air pollutants were positively associated with ischemic stroke and intracerebral hemorrhage mortality, both air pollutants were more strongly associated with subarachnoid hemorrhage mortality: rate ratio was 1.041 (95% confidence interval: 1.011-1.072) for each 10 μg/m3 increase in the previous-day particles less than 2.5 μm. CONCLUSIONS: This study suggests that short-term exposure to outdoor air pollution increases the risks of hemorrhagic stroke mortality as well as ischemic stroke mortality.