Short term exposure to air pollution and stroke: systematic review and meta-analysis

OBJECTIVE To review the evidence for the short term association between air pollution and stroke. DESIGN Systematic review and meta-analysis of observational studies DATA SOURCES Medline, Embase, Global Health, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Web of Science searched to January 2014 with no language restrictions. ELIGIBILITY CRITERIA Studies investigating the short term associations (up to lag of seven days) between daily increases in gaseous pollutants (carbon monoxide, sulphur dioxide, nitrogen dioxide, ozone) and particulate matter (< 2.5 mu m or < 10 mu m diameter (PM2.5 and PM10)), and admission to hospital for stroke or mortality. MAIN OUTCOME MEASURES Admission to hospital and mortality from stroke. RESULTS From 2748 articles, 238 were reviewed in depth with 103 satisfying our inclusion criteria and 94 contributing to our meta-estimates. This provided a total of 6.2 million events across 28 countries. Admission to hospital for stroke or mortality from stroke was associated with an increase in concentrations of carbon monoxide (relative risk 1.015 per 1 ppm, 95% confidence interval 1.004 to 1.026), sulphur dioxide (1.019 per 10 ppb, 1.011 to 1.027), and nitrogen dioxide (1.014 per 10 ppb, 1.009 to 1.019). Increases in PM2.5 and PM10 concentration were also associated with admission and mortality (1.011 per 10 (I) over cap1/4g/m(3) (1.011 to 1.012) and 1.003 per 10 mu g/m(3) (1.002 to 1.004), respectively). The weakest association was seen with ozone (1.001 per 10 ppb, 1.000 to 1.002). Strongest associations were observed on the day of exposure with more persistent effects observed for PM2-5. CONCLUSION Gaseous and particulate air pollutants have a marked and close temporal association with admissions to hospital for stroke or mortality from stroke. Public and environmental health policies to reduce air pollution could reduce the burden of stroke.