Long-term exposure to ambient PM and stroke mortality among urban residents in northern China.

Evidence is still limited for the role of long-term PM exposure in cerebrovascular diseases among residents in high pollution regions. The study is aimed to investigate the long-term effects of PM exposure on stroke mortality, and further explore the effect modification of temperature variation on the PM-mortality association in northern China. Based on a cohort data with an average follow-up of 9.8 years among 38,435 urban adults, high-resolution estimates of PM derived from a satellite-based model were assigned to each participant. A Cox regression model with time-varying exposures and strata of geographic regions was employed to assess the risks of stroke mortality associated with PM, after adjusting for individual risk factors. The cross-product term of PM exposure and annual temperature range was further added into the regression model to test whether the long-term temperature variation would modify the association of PM with stroke mortality. Among the study participants, the annual mean level of PM concentration was 66.3 μg/m ranging from 39.0 μg/m to 100.6 μg/m. For each 10 μg/m increment in PM, the hazard ratio (HR) was 1.31 (95% CI: 1.04-1.65) for stroke mortality after multivariable adjustment. In addition, the HRs of PM decreased gradually as the increase of annual temperature range with the HRs of 1.95 (95% CI: 1.36-2.81), 1.53 (95% CI: 1.06-2.22), and 1.11 (95% CI: 0.75-1.63) in the low, middle, and high group of annual temperature range, respectively. The findings provided further evidence of long-term PM exposure on stroke mortality in high-exposure settings such as northern China, and also highlighted the view that assessing the adverse health effects of air pollution might not ignore the role of temperature variations in the context of climate change.