• Cui Guo, Tsung Yu, Ly-Yun Chang, Changqing Lin, Hsiao Ting Yang, Yacong Bo, Yiqian Zeng, Tony Tam, Alexis K H Lau, and Xiang Qian Lao.
• Jockey Club School of Public Health and Primary Care (Guo, Yang, Bo, Zeng, Lao), the Chinese University of Hong Kong, Hong Kong SAR, China; Department of Public Health (Yu), National Cheng Kung University, Tainan, Taiwan; Institute of Sociology (Chang), Academia Sinica, Taipei, Taiwan; Division of Environment and Sustainability (Lin, Lau), the Hong Kong University of Science and Technology, Hong Kong SAR, China; Department of Civil and Environmental Engineering (Lau), the Hong Kong University of Science and Technology, Hong Kong SAR, China; Department of Nutrition and Food Hygiene (Bo), School of Public Health, Zhengzhou University, China; Department of Sociology (Tam), the Chinese University of Hong Kong, Hong Kong SAR, China; Shenzhen Research Institute of the Chinese University of Hong Kong (Lao), Shenzhen, China.
• CMAJ. 2021 Aug 16; 193 (32): E1240-E1249.

BackgroundExercise may exacerbate the adverse health effects of air pollution by increasing the inhalation of air pollutants. We investigated the combined effects of long-term exposure to fine particle matter (PM2.5) and habitual exercise on deaths from natural causes in Taiwan.MethodsWe recruited 384 130 adults (aged ≥ 18 yr) with 842 394 medical examination records between 2001 and 2016, and followed all participants until May 31, 2019. We obtained vital data from the National Death Registry of Taiwan. We estimated PM2.5 exposure using a satellite-based spatiotemporal model, and collected information on exercise habits using a standard self-administered questionnaire. We analyzed the data using a Cox regression model with time-dependent covariates.ResultsA higher level of habitual exercise was associated with a lower risk of death from natural causes, compared with inactivity (hazard ratio [HR] 0.84, 95% confidence interval [CI] 0.80-0.88 for the moderate exercise group; HR 0.65, 95% CI 0.62-0.68 for the high exercise groups), whereas a higher PM2.5 exposure was associated with a higher risk of death from natural causes compared with lower exposure (HR 1.02, 95% CI 0.98-1.07, and HR 1.15, 95% CI 1.10-1.20, for the moderate and high PM2.5 exposure groups, respectively). Compared with inactive adults with high PM2.5 exposure, adults with high levels of habitual exercise and low PM2.5 exposure had a substantially lower risk of death from natural causes. We found a minor, but statistically significant, interaction effect between exercise and PM2.5 exposure on risk of death (HR 1.03 95% CI 1.01-1.06). Subgroup analyses, stratified by PM2.5 categories, suggested that moderate and high levels of exercise were associated with a lower risk of death in each PM2.5 stratum, compared with inactivity.InterpretationIncreased levels of exercise and reduced PM2.5 exposure are associated with a lower risk of death from natural causes. Habitual exercise can reduce risk regardless of the levels of PM2.5 exposure. Our results suggest that exercise is a safe health improvement strategy, even for people residing in relatively polluted regions.© 2021 CMA Joule Inc. or its licensors.

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