Impact of Outdoor Air Pollution on Survival After Stroke

BACKGROUND AND PURPOSE: The impact of air pollution on survival after stroke is unknown. We examined the impact of outdoor air pollution on stroke survival by studying a population-based cohort. METHODS: All patients who experienced their first-ever stroke between 1995 and 2005 in a geographically defined part of London, where road traffic contributes to spatial variation in air pollution, were followed up to mid-2006. Outdoor concentrations of nitrogen dioxide and particulate matter <10 microm in diameter modeled at a 20-m grid point resolution for 2002 were linked to residential postal codes. Hazard ratios were adjusted for age, sex, social class, ethnicity, smoking, alcohol consumption, prestroke functional ability, pre-existing medical conditions, stroke subtype and severity, hospital admission, and neighborhood socioeconomic deprivation. RESULTS: There were 1856 deaths among 3320 patients. Median survival was 3.7 years (interquartile range, 0.1 to 10.8). Mean exposure levels were 41 microg/m(3) (SD, 3.3; range, 32.2 to 103.2) for nitrogen dioxide and 25 microg/m(3) (SD, 1.3; range, 22.7 to 52) for particulate matter <10 microm in diameter. A 10-microg/m(3) increase in nitrogen dioxide was associated with a 28% (95% CI, 11% to 48%) increase in risk of death. A 10-microg/m(3) increase in particulate matter <10 mum in diameter was associated with a 52% (6% to 118%) increase in risk of death. Reduced survival was apparent throughout the follow-up period, ruling out short-term mortality displacement. CONCLUSIONS: Survival after stroke was lower among patients living in areas with higher levels of outdoor air pollution. If causal, a 10-microg/m(3) reduction in nitrogen dioxide exposure might be associated with a reduction in mortality comparable to that for stroke units. Improvements in outdoor air quality might contribute to better survival after stroke.