Air pollution weakens the life-extending benefits of exercise

By Tarun Sai LomteReviewed by Lauren HardakerDec 3 2025

A large multi-country study identifies the air pollution levels at which the health benefits of regular physical activity start to decline, offering clearer guidance for staying active in areas with rising PM2.5 exposure.

Study: 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. Image credit: Lordn/Shutterstock.com

In a recent study published in BMC Medicine, researchers investigated whether increased levels of exposure to fine particulate matter (PM_2.5) impact the protective effects of leisure-time physical activity (LTPA) on mortality.

LTPA is associated with lower risks of morbidity and mortality; however, outdoor LTPA increases exposure to air pollution, including PM_2.5. Long-term PM_2.5 exposure is linked to higher morbidity and mortality, and was identified as a leading contributor to global disease burden. As such, there are concerns that PM_2.5 exposure may offset the beneficial effects of LTPA on mortality.

Linking exercise benefits to pollution levels

In the present study, researchers investigated whether exposure to PM2.5 reduces the protective association of LTPA with mortality. First, Medline, Embase, Web of Science, and SPORTDiscus databases were searched for cohort studies investigating the relationships of PM_2.5 and LTPA with mortality in adult populations.

Eligible studies were longitudinal studies that included adults aged 18 years or older and reported independent or joint associations of LTPA and PM_2.5 with mortality, providing relative risk estimates or hazard ratios. Studies that involved clinical populations, measured LTPA without estimating energy expenditure of LTPA, or focused on overall physical activity or non-LTPA were excluded.

LTPA data in studies were obtained using self-reported questionnaires; LTPA was calculated as metabolic equivalent task-hours (MET-h) per week and stratified into four categories: least active (< 1 MET-h/week), insufficiently active (1–7.5 MET-h/week), recommended (7.5–15 MET-h/week), and highly active (> 15 MET-h/week).

Summary data from included studies were used to explore the relationships between LTPA and all-cause mortality. Two random-effects subgroup analyses were conducted to examine dose-response relationships. One analysis explored LTPA-mortality associations within studies, and the other investigated these associations at different levels of ambient PM_2.5.

Meta-regression analyses examined whether the effects of LTPA on mortality were influenced by PM2.5 levels, while adjusting for the mean age of the sample and the percentage of females. Further, the team pooled individual-level data from three cohorts (the United Kingdom Biobank, Taiwan Biobank, and Taiwan MJ cohort) to examine associations of LTPA with all-cause, cancer, and cardiovascular mortality across a broader spectrum of PM_2.5 exposure.

Exercise benefits fall as PM2.5 concentrations rise

A database search identified 756 studies; following deduplication and title/abstract screening, full-text analysis of 20 studies resulted in the identification of four eligible studies. Additionally, three studies from excluded publications were identified as potentially having unpublished results. As such, seven studies were included in the analyses, which encompassed 1.51 million people followed up for a median of 12.3 years and reported 115,196 deaths.

Increased engagement in LTPA was progressively associated with lower all-cause mortality in each study. Nonetheless, these benefits of LTPA on mortality were reduced with higher PM_2.5 levels. Moreover, engaging in recommended levels of LTPA was associated with a 30 % reduction in the risk of mortality at PM_2.5 < 25 μg/m³; however, at PM_2.5 > 25μg/m³, it was associated with 12 % to 15 % decrease in mortality risk.

Meta-regression analyses indicated that greater engagement in LTPA was associated with reduced mortality, and PM2.5 levels significantly weakened this effect. However, most individual cohorts did not show statistically significant LTPA–PM2.5 interaction effects, and reduction became evident only when data were pooled across broader PM2.5 ranges. This protective effect was not significantly different across PM_2.5 categories < 25 μg/m³. However, at PM_2.5 > 25 μg/m³, the protective associations were attenuated, increasing the risk of mortality.

The pooled analysis of individual-level data included 869,038 individuals, with 45,080 deaths. Both PM_2.5 and LTPA were independently associated with all-cause mortality in the pooled analysis, with lower levels of PM_2.5 and higher levels of LTPA being significantly associated with a lower mortality risk.

In the joint association analysis, individuals meeting the recommended levels of LTPA had a lower risk of all-cause mortality compared to those in the highest-risk group, i.e., those who were least active and exposed to PM2.5 levels of 35 to 50 μg/m³.

For individuals meeting or exceeding the recommended levels of LTPA, the associations stratified by sex, age group, and the presence of cardiovascular diseases were similar to those observed in the overall sample. Furthermore, the joint associations with cardiovascular or cancer mortality were comparable to those observed for all-cause mortality, with the protective effects of LTPA reduced at PM2.5 levels greater than 25 μg/m³ and becoming non-significant, primarily for cancer mortality, at levels greater than 35 μg/m³.

LTPA remains helpful, but pollution limits its impact

Engaging in LTPA was beneficial for all-cause, cancer, and cardiovascular mortality even at high levels of PM_2.5 exposure. However, the protective effects began to decrease at PM_2.5 levels > 25 μg/m³_. At 35 to 50 μg/m³ the benefits were notably weakened, particularly for cancer mortality.

These association patterns remained consistent across age groups, sex, and people with cardiovascular disease. Overall, these results underscore the importance of considering air quality in public health and physical activity guidelines.

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