Short-term associations of ambient air pollution with hospital admissions for ischemic stroke in 97 Japanese cities

The short-term association between ambient air pollution and hospital admissions for ischemic stroke is not fully understood. We examined the association between four regularly measured major ambient air pollutants, i.e., sulfur dioxide (SO2), nitrogen dioxide (NO2), photochemical oxidants (Ox), and particulate matter with aerodynamic diameters ≤ 2.5 μm (PM2.5), and hospital admissions for ischemic stroke by analyzing 3 years of nationwide claims data from 97 cities in Japan. We first estimated city-specific results by using generalized additive models with a quasi-Poisson regression, and we obtained the national average by combining city-specific results with the use of random-effect models. We identified a total of 335,248 hospital admissions for ischemic stroke during the 3-year period. Our analysis results demonstrated that interquartile range increases in the following four ambient air pollutants were significantly associated with hospital admissions for ischemic stroke on the same day: SO2 (1.05 ppb), 1.05% (95% CI: 0.59–1.50%); NO2 (6.40 ppb), 1.10% (95% CI: 0.61–1.59%); Ox (18.32 ppb), 1.43% (95% CI: 0.81–2.06%); and PM2.5 (7.86 μg/m3), 0.90% (95% CI: 0.35–1.45%). When the data were stratified by the hospital admittees’ medication use, we observed stronger associations with SO2, NO2, and PM2.5 among the patients who were taking antihypertensive drugs and weaker associations with SO2, NO2, and Ox among those taking antiplatelet drugs. Short-term exposure to ambient air pollution was associated with increased hospital admissions for ischemic stroke, and medication use and season may modify the association.