Ambient Particulate Matter and the Risk of Stroke
Stroke is a leading cause of long-term disability and the third leading cause of death after heart disease and cancer, both in the United States and globally. A large number of epidemiologic studies have found associations between short-term and long-term increases in particulate air pollution (PM) and risk of cardiovascular morbidity and mortality. However, the potential effects of PM on cerebrovascular morbidity and mortality have only recently been studied in detail. Large studies from the US, Europe, and Australia/New Zealand provide inconsistent support for an association between short-term increases in ambient PM levels and risk of cerebrovascular disease morbidity or mortality. The evidence in support of an association is more consistent among studies that have specifically evaluated hospitalization for ischemic stroke, although again, considerable heterogeneity across studies is observed. In contrast, findings from both ecological and cohort studies consistently show that long-term exposure to ambient PM is associated with increased risk of cerebrovascular morbidity and mortality. Given the well documented associations between ambient PM exposure and cardiac disease, as well as the putative mechanisms of these effects, it is plausible that ambient PM increase the risk of ischemic and/or hemorrhagic stroke. Studies to date broadly support this hypothesis, but additional studies are clearly needed.