A large-scale international study has found that long-term exposure to fine particulate air pollution substantially reduces the protective effect of regular physical activity against premature death. Drawing on data from more than 1.5 million adults across several countries, the research shows that exercise’s life-extending benefits are markedly weaker in areas with high levels of PM2.5 pollution, underscoring the importance of cleaner air to maximise health gains.
An international team of researchers, including experts from University College London (UCL), has published a study in BMC Medicine examining how air pollution influences the health benefits of physical activity. The analysis drew on seven cohort studies involving more than 1.5 million adults who were monitored for over a decade in countries including the UK, Taiwan, China, Denmark and the United States, according to a summary from UCL released via ScienceDaily.
The researchers combined summary data from all seven cohorts and individual participant records from three of them, three of which had not been previously published, to assess how pollution levels might modify exercise-related reductions in mortality risk.
The study focused on fine particulate matter known as PM2.5 — particles smaller than 2.5 micrometres that can penetrate deep into the lungs and even enter the bloodstream. Across the pooled datasets, adults who completed at least two and a half hours of moderate to vigorous exercise per week — such as jogging or other activities that cause breathlessness and perspiration — had about a 30% lower risk of death from any cause during the study period compared with people who did not reach this activity level.
However, the ScienceDaily summary of the BMC Medicine paper reports that in regions where annual average PM2.5 levels reached 25 micrograms per cubic metre (µg/m³) or higher, this protective effect fell to around 12–15% for highly active individuals. The analysis also indicates that nearly half of the world’s population, about 46%, lives in areas at or above this 25 µg/m³ threshold.
When yearly PM2.5 concentrations exceeded 35 µg/m³, the benefit of exercise weakened further, particularly for deaths linked to cancer, and the protective effects were no longer strong. The authors estimate that about 36% of the global population lives in places where annual PM2.5 averages surpass 35 µg/m³.
Lead researcher Professor Po-Wen Ku of National Chung Hsing University in Taiwan said in the UCL statement: "Our findings emphasize that exercise remains beneficial even in polluted environments. However, improving air quality can greatly enhance these health gains."
Co-author Professor Andrew Steptoe from UCL's Department of Behavioural Science & Health added: "Our study shows that toxic air can to some extent block the benefits of exercise, although not eliminate them. The findings are further evidence of the damage that fine particle pollution can do to our health.
"We believe clean air and physical activity are both important for healthy aging and so we encourage greater efforts to curb health-harming pollution levels."
Participants from the UK in the pooled analysis experienced average PM2.5 levels of around 10 µg/m³, below the thresholds at which the study found strong reductions in the benefits of exercise. However, pollution in UK cities varies considerably, and the researchers note that wintertime spikes often push concentrations above 25 µg/m³, the critical level at which exercise-related protection begins to shrink.
Co-author Professor Paola Zaninotto from UCL's Department of Epidemiology & Public Health said: "We don't want to discourage people from exercising outdoors. Checking air quality, choosing cleaner routes, or easing off intensity on polluted days can help you get the most health benefits from your exercise."
The authors report that the study accounted for a wide range of potential confounding factors, including income, education, smoking habits and existing chronic conditions. They also outlined several limitations, such as the predominance of data from high-income countries and gaps in information on indoor air quality and diet, which could affect how widely the findings can be applied, particularly in lower-income regions with much higher pollution levels.
According to the ScienceDaily summary, funding for the research was provided by Taiwan's National Science and Technology Council, Taichung Veterans General Hospital and National Chung Hsing University.
