Yacong Bo and Xiang Qian Lao
Regular exercise is recognised as providing significant lifestyle-related protection against non-communicable diseases. It can also reduce the likelihood of cardiovascular disease, cancer and premature death. By contrast, long-term exposure to fine particulate matter (PM2.5) can increase the likelihood of respiratory and cardiovascular disease and certain cancers, leading to premature death.
Outdoor exercise might increase the inhalation and deposition of air pollutants, potentially counteracting its beneficial effects. Evaluation of this risk–benefit relationship has become an important public health concern because more than 91% of the global population lives in areas where air quality fails to meet the 2005 World Health Organization guidelines.
In our study, recently published in the International Journal of Epidemiology, we examined the combined effects of PM2.5 exposure and exercise on the likelihood of dying from cancer in Taiwan. The large study was conducted over 15 years, from 2001 to 2016, with more than 384,000 adults living in areas with relatively high levels of air pollution (the 2-year average PM2.5 concentration was 26 μg/m3, 2.6 times higher than the 2005 WHO guideline value of 10 μg/m3 for annual average PM2.5).
We adjusted our analysis by including known cancer risk factors — age, sex, education, body mass index, physical labour at work, cigarette smoking, alcohol consumption, fruit and vegetable intake, occupational exposure and the season when physical examination was conducted — as covariates.
Among our study population, we identified 5690 cancer-related deaths during the following 19 years. We found that people with habitually high levels of exercise had a 24% lower likelihood of dying from cancer than inactive people. Stratification by different levels of PM2.5 exposure showed that people with high levels of exercise had a 30%, 16% and 25% lower likelihood of death from cancer than inactive people in low, moderately and highly polluted areas, respectively.
We also observed that the adverse health effects of air pollution generally manifested at different levels of habitual exercise. Compared with people in areas of low pollution, those in highly polluted areas who were highly and moderately active had a 20% and 19% higher likelihood of cancer mortality, respectively. Finally, participants with high levels of exercise and low levels of PM2.5 exposure had a 35% lower likelihood of cancer mortality than those with low levels of exercise and high levels of PM2.5 exposure.
The beneficial effects of habitual exercise were observed in different levels of ambient PM2.5, and the adverse effects of exposure to PM2.5 generally manifested with different levels of habitual exercise. In other words, regular exercise reduces the likelihood of death from cancer regardless of the level of chronic PM2.5 exposure.
Regular exercise is an effective and safe strategy to prevent premature death caused by cancer, even for people living in polluted areas. People should not have to choose between doing exercise and avoiding air pollution. However, as the beneficial effects of habitual exercise are higher in low polluted areas, it might be better to exercise in places with less traffic or greener surroundings. In areas of severe air pollution, indoor exercise might be better.
Bo Y, Yu T, Chang LY, et al. Combined effects of chronic PM2.5 exposure and habitual exercise on cancer mortality: a longitudinal cohort study. Int J Epidemiol 2021; 11 October. doi: 10.1093/ije/dyab209.
Yacong Bo (@YacongB) is a postdoctoral fellow in the Jockey Club School of Public Health and Primary Care at the Chinese University of Hong Kong. Her research interests focus on the health effects of air pollution on non-communicable diseases.
Xiang Qian Lao (@XiangQianLao1) is a professor of air pollution epidemiology at the Jockey Club School of Public Health and Primary Care at the Chinese University of Hong Kong. His research focuses on the health effects of air pollution on non-communicable diseases and the combined health effects of air pollution and physical exercise.