Physical activity, air pollution, and mortality: a systematic review and meta-analysis

Background
As whether the positive effects of physical activity on mortality outweigh the negative effects of exposure to pollution is still under debate, we conducted a systematic review and meta-analysis on the risk of mortality for combined exposure to physical activity and air pollution.

Methods
PubMed, Cochrane, Embase and ScienceDirect databases were searched for studies assessing the risk of mortality for combined exposure to physical activity and air pollution.

Results
We included eight studies for a total of 1,417,945 individuals (mean 57.7 years old, 39% men) – 54,131 died. We confirmed that air pollution increased the risk of mortality by 36% (OR 1.36, 95CI 1.05–1.52), whereas physical activity in a non-polluted environment decreased the risk of mortality by 31% (OR 0.69, 95CI 0.42–0.95). Our meta-analysis demonstrated that combined exposure to physical activity and air pollution decreased the risk of mortality by 26% (OR 0.74, 95CI 0.63–0.85). This risk decreased whatever the level of physical activity: by 19% (OR 0.81, 95CI 0.69–0.93) for low, by 32% (OR 0.68, 95CI 0.44–0.93) for moderate, and by 30% (OR 0.70, 95CI 0.49–0.91) for high physical activity in air pollution.

Conclusion
We confirmed that air pollution increased mortality by 36% in our meta-analysis. Despite the controversial benefit-risk, we demonstrated a reduction of mortality by 26% for combined exposure to physical activity and air pollution – nearly comparable to the reduction of mortality when practicing physical activity without air pollution (− 31%). However, the limited number of included studies precluded the demonstration of a dose–response relationship between levels of physical activity and air pollution, and reduction of mortality.