Short-Term Exposure to Fine Particulate Matter and Risk of Ischemic Stroke

<jats:sec> <jats:title>Background and Purpose—</jats:title> <jats:p> There is a strong association between ambient concentrations of particulate matter (PM) and cardiovascular disease. However, it remains unclear whether acute exposure to fine PM (PM <jats:sub>2.5</jats:sub> ) triggers ischemic stroke events and whether the timing of exposure is associated with stroke risk. We, therefore, examined the association between ambient PM <jats:sub>2.5</jats:sub> and occurrence of ischemic stroke. </jats:p> </jats:sec> <jats:sec> <jats:title>Methods—</jats:title> <jats:p> We analyzed data for 6885 ischemic stroke patients from a multicenter hospital-based stroke registry in Japan who were previously independent and hospitalized within 24 hours of stroke onset. Time of symptom onset was confirmed, and the association between PM (suspended PM and PM <jats:sub>2.5</jats:sub> ) and occurrence of ischemic stroke was analyzed by time-stratified case-crossover analysis. </jats:p> </jats:sec> <jats:sec> <jats:title>Results—</jats:title> <jats:p> Ambient PM <jats:sub>2.5</jats:sub> and suspended PM at lag days 0 to 1 were associated with subsequent occurrence of ischemic stroke (ambient temperature–adjusted odds ratio [95% confidence interval] per 10 μg/m <jats:sup>3</jats:sup> : suspended PM, 1.02 [1.00–1.05]; PM <jats:sub>2.5</jats:sub> , 1.03 [1.00–1.06]). In contrast, ambient suspended PM and PM <jats:sub>2.5</jats:sub> at lag days 2 to 3 or 4 to 6 showed no significant association with stroke occurrence. The association between PM <jats:sub>2.5</jats:sub> at lag days 0 to 1 and ischemic stroke was maintained after adjusting for other air pollutants (nitrogen dioxide, photochemical oxidants, or sulfur dioxide) or influenza epidemics and was evident in the cold season. </jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions—</jats:title> <jats:p> These findings suggest that short-term exposure to PM <jats:sub>2.5</jats:sub> within 1 day before onset is associated with the subsequent occurrence of ischemic stroke. </jats:p> </jats:sec>