Air pollution — even for just one day — significantly increases the risk of stroke, a large review of studies has found.
Researchers pooled data from 103 studies involving 6.2 million stroke hospitalizations and deaths in 28 countries.
The analysis, published online in BMJ, found that all types of pollution except ozone were associated with increased risk for stroke, and the higher the level of pollution, the more strokes there were.
Daily increases in pollution from nitrogen dioxide, sulfur dioxide, carbon monoxide and particulate matter were associated with corresponding increases in strokes and hospital admissions. The 
strongest associations were apparent on the day of exposure, but increases in particulate matter had longer-lasting effects.
The exact reason for the effect is unclear, but studies have shown that air pollution can constrict blood vessels, increase blood pressure and increase the risk for blood clots. Other research has tied air pollution to a higher risk of heart attacks, stroke and other ills.
Source: New York Times