Does regular exercise protect against air pollution-associated mortality?

Objectives. To examine whether habitual exercise would modify the effects of air pollution on mortality. Methods. This study included 24,053 Hong Kong Chinese who died at the age of 30 years or older in 1998. Individual information on frequency of exercise was obtained by interviewing their relatives at all four death registries. The deceased subjects were categorized as never-exercise (< once/month) and exercise (≥ once/month). Excess risks (ER) of mortality per 10 μg/m3 increase of air pollutant were estimated separately by a Poisson regression model in the exercise and never-exercise groups. An interaction model was used to estimate the difference in ER between the two groups. Results. In people aged 65 years or older and categorized as never-exercise group, there were significant ER of mortality for all natural causes attributed to nitrogen dioxide (p < 0.05), ozone (p < 0.05) and particulate matter with an aerodynamic diameter of 10 μm or smaller (p < 0.01). When compared to the exercise group, the ER were significantly higher by 4.31% (95% confidence interval: 2.57%, 6.03%), 1.75% (0.25%, 3.23%), and 3.06% (1.74%, 4.37%), respectively. The estimates were insensitive to adjustment for socioeconomic, smoking and health status, and were non-linear by different exercise levels. Conclusions. The results of this study provide evidence that habitual exercise may prevent premature death attributable to air pollution.