Polluted air quietly erases the benefits of exercise

The study, published in BMC Medicine, examined information from over 1.5 million adults who were monitored for more than ten years across several countries, including the UK, Taiwan, China, Denmark and the United States.

Researchers found that people living in areas with substantial air pollution experienced a noticeably smaller reduction in their risk of death during the study period. This applied to deaths from any cause, as well as from cancer and heart disease specifically, although some benefit from exercise still remained.

Fine Particle Pollution and Its Impact on the Body

The team focused on levels of fine particulate matter, or PM2.5s, which are extremely small particles less than 2.5 micrometers in diameter. Because of their size, they can travel deep into the lungs and even enter the bloodstream.

The analysis showed that exercise benefits declined sharply when yearly average PM2.5 levels reached 25 micrograms per cubic meter (μg/m³) or higher. Nearly half (46%) of the global population lives in regions where pollution is at or above this level.

Lead researcher Professor Po-Wen Ku of National Chung Hsing University, Taiwan, said: "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."

Large-Scale Analysis Reveals Clear Risk Patterns

To conduct the investigation, the research team combined data from seven existing studies, three of which had not previously been published. They included both summary data and, for three studies, a new analysis of individual participant records.

Across all studies, adults who completed at least two and a half hours of moderate or vigorous exercise* each week had a 30% lower risk of death during the study period compared with people who did not reach this level of activity.

For highly active people living in areas where PM2.5 pollution exceeded 25 μg/m³, this protective effect dropped to just 12-15%.

Higher Pollution Levels Further Reduce Exercise Benefits

When pollution levels rose above 35 μg/m³, the benefit of exercise weakened even more, particularly for deaths linked to cancer. In these conditions, the protective effects were no longer strong. About 36% of the global population lives in places where yearly PM2.5 averages exceed 35 μg/m³.

Participants from the UK experienced average PM2.5 levels of 10 μg/m³, which are below the thresholds associated with strong reductions in exercise benefits. However, pollution in UK cities fluctuates significantly, and wintertime spikes commonly exceed 25 μg/m³, the study's critical threshold.

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."

Study Limitations and Broader Context

The authors noted several limitations. Most of the data came from high-income countries, so the conclusions may not fully apply to low-income regions where pollution levels are often much higher, sometimes surpassing 50 μg/m³. Additional missing information included indoor air quality and details about participants' diets.

Despite these gaps, the research accounted for many other variables, such as income, education, smoking habits, and whether participants had existing chronic conditions.

Researchers from the UK, the United States, Australia and Asia participated in the project. The UK analysis used data from the UK Biobank.

Funding for the study was provided by Taiwan's National Science and Technology Council, Taichung Veterans General Hospital (TCVGH) and National Chung Hsing University.

Notes

*Moderate to vigorous exercise, such as jogging or other sports, is often defined as an activity that makes people breathless and causes perspiration.