Ku, Po-Wen; Steptoe, Andrew; Hamer, Mark; Zaninotto, Paola; Stamatakis, Emmanuel; Lin, Ching-Heng; Yu, Bin; ... Chen, Li-Jung; + view all Ku, Po-Wen; Steptoe, Andrew; Hamer, Mark; Zaninotto, Paola; Stamatakis, Emmanuel; Lin, Ching-Heng; Yu, Bin; Hvidtfeldt, Ulla Arthur; Lao, Xiang Qian; Lin, Hsien-Ho; Lo, Wei-Cheng; Raaschou-Nielsen, Ole; Sun, Shengzhi; Tian, Linwei; Wang, Su-Fen; Zeng, Yiqian; Zhang, Yunquan; Chen, Shang-Ti; Huang, Chien-Fong; Xia, Yang; Chen, Li-Jung; - view fewer (2025) Does ambient PM2.5 reduce the protective association of leisure-time physical activity with mortality? A systematic review, meta-analysis, and individual-level pooled analysis of cohort studies involving 1.5 million adults. BMC Medicine , 23 , Article 647. 10.1186/s12916-025-04496-y.

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Abstract

Background: This study assessed whether higher levels of fine particulate matter (PM2.5) reduce the protective effects of leisure-time physical activity (LTPA) on all-cause, cardiovascular, and cancer mortality, and explored the PM2.5 threshold beyond which attenuation occurs. // Methods: We conducted two complementary investigations. First, a systematic review and meta-analysis (per PRISMA guidelines) identified eligible cohort studies from PubMed, Web of Science, Embase, and SPORTDiscus (from inception to 6 January 2025) that examined the independent or joint associations of LTPA and PM₂.₅ with mortality among adults (≥ 18 years). Second, an individual-level pooled analysis using harmonized data from three cohorts was performed using Cox regression modeling to assess the associations observed in the meta-analysis. // Results: In Study One, a total of seven cohort studies (n = 1,515,094; deaths = 115,196) were included in the meta-analysis, revealing that the reduction in all-cause mortality risk diminished with higher PM2.5 exposure. Meeting the recommended LTPA level (7.5–15 MET-h/week) reduced all-cause mortality risk by approximately 30% at PM2.5 < 25 μg/m3 but only 12–15% at 25 + μg/m3. Study Two (three cohorts; n = 869,038; deaths = 45,080) confirmed this pattern. Individuals meeting the recommended LTPA level (7.5–15 MET-h/week) had a lower risk of all-cause mortality compared to those in the highest-risk group (reference: < 1 MET-h/week and PM2.5: 35–50 μg/m3). Hazard ratios (HRs) varied by PM2.5 exposure, with lower HRs indicating a greater protective effect: 35–50 μg/m3 (HR = 0.75, 95% CI: 0.61–0.93), 25–35 μg/m3 (HR = 0.67, 95% CI: 0.57–0.79), 15–25 μg/m3 (HR = 0.34, 95% CI: 0.29–0.39), 10–15 μg/m3 (HR = 0.34, 95% CI: 0.28–0.41), and < 10 μg/m3 (HR = 0.30, 95% CI: 0.25–0.37). Higher levels of LTPA were generally associated with lower all-cause and cause-specific mortality across most PM₂.₅ exposure categories, but the protective effects were attenuated at PM₂.₅ levels 25 + μg/m3 for all outcomes and became non-significant for cancer mortality at 35–50 μg/m3. // Conclusions: LTPA is beneficial for all-cause, cardiovascular, and cancer mortality even at relatively high PM2.5 levels, with greater benefits observed under cleaner air conditions. However, its protective effects are attenuated at 25 + μg/m3 for all outcomes and become less evident at 35–50 μg/m3, particularly for cancer mortality. // PROSPERO Registration Number: CRD42023395364.

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