An evidence-based appraisal of global association between air pollution and risk of stroke

- The adverse transient effects of air pollution on stroke are inconclusive.
- Meta-analytic approach was used to assess these transient effects of air pollution.
- Air pollution may increase the risk of stroke hospitalizations and mortality.
- These positive associations appeared to be more apparent for ischemic stroke.
- These positive associations appeared to be more apparent among Asian populations.

BackgroundThe aim of this study was to evaluate the transient effects of air pollutants on stroke morbidity and mortality using the meta-analytic approach.MethodsThree databases were searched for case-crossover and time series studies assessing associations between daily increases in particles with diameter < 2.5 μm (PM2.5) and diameter < 10 μm (PM10), sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), ozone, and risks of stroke hospitalizations and mortality. Risk estimates were combined using random-effects model.ResultsA total of 34 studies were included in the meta-analysis. Stroke hospitalizations or mortality increased 1.20% (95%CI: 0.22-2.18) per 10 μg/m3 increase in PM2.5, 0.58% (95%CI: 0.31-0.86) per 10 μg/m3 increase in PM10, 1.53% (95%CI: 0.66-2.41) per 10 parts per billion (ppb) increase in SO2, 2.96% (95%CI: 0.70-5.27) per 1 ppm increase in CO, and 2.24% (95%CI: 1.16-3.33) per 10 ppb increase in NO2. These positive associations were the strongest on the same day of exposure, and appeared to be more apparent for ischemic stroke (for all 4 gaseous pollutants) and among Asian countries (for all 6 pollutants). In addition, an elevated risk (2.45% per 10 ppb; 95%CI: 0.35-4.60) of ischemic stroke associated with ozone was found, but not for hemorrhagic stroke.ConclusionOur study indicates that air pollution may transiently increase the risk of stroke hospitalizations and stroke mortality. Although with a weak association, these findings if validated may be of both clinical and public health importance given the great global burden of stroke and air pollution.