Background Stroke is the third most common cause of death in Taiwan. However, the reasonable range in time scale of air pollution concentration for inducing ischemic stroke has not been clear. Therefore, the purpose of the study was to examine the effect of time scale air pollution concentration and stroke risk.

Methods We recruited 256 ischemic stroke patients in emergency department and 98 healthy controls from a Taiwan Medical Center between 2012 and 2013. The subjects were interviewed in person and completed the demographic, disease history questionnaires. Each participant provided blood samples for metal and oxidative stress measurements. We used the geographic information system (GIS) and the Inverse distance weighting (IDW) model to estimate the concentrations of air pollutants (PM2.5, PM10, SO2, NO2, CO, O3) at home address from 75 monitoring stations in Taiwan at different time scales (1 day, 2 days, 3 days, 7 days, 14 days, 1 month, 7 months, 1 year) before blood drawing. Logistic regression models were performed to estimate the odds ratio (OR) for stroke risk.

Results The interquartile range (IQR) PM2.5 concentrations were 17.5, 16.3, 14.5, 14.4, 12.0, 9.2, 6.6, and 1.9 µg/m3 respectively, for different time scales within 1 day, 2 days, 3 days, 7 days, 14 days, 1 month, 7 months, 1 year period before stroke onset. We found that the 7 days, 14 days, 1 month PM2.5 concentrations were significantly increased risk of stroke, after adjustment for smoking, environmental tobacco smoke, ever stroke, family history of stroke, hypertension, hyperlipidemia, type 2 diabetes, heart disease history, temperature, and relative humidity. The results also showed that elevated stroke risks with 2 days, 3 days, 7 days, 14 days, 1 month PM10, and with 7 days, 14 days, and 1 month O3.