England

Research from University College London (UCL) indicates that long-term exposure to polluted air can considerably reduce the health benefits of regular exercise.

The study analysed data from over 1.5 million adults tracked for more than ten years across countries including the UK, Taiwan, China, Denmark, and the US.

Researchers discovered that while regular physical activity still offers protective effects against overall mortality, cancer, and heart disease, these benefits are diminished for individuals living in areas with high pollution levels.

The team focused on fine particulate matter, or PM2.5, tiny particles less than 2.5 micrometres in diameter that can lodge in the lungs and enter the bloodstream. They found that exercise benefits were significantly weakened when annual average PM2.5 levels exceeded 25 micrograms per cubic metre (µg/m³)—a threshold exceeded by nearly 46% of the global population.

Professor Po-Wen Ku of National Chung Hsing University, Taiwan, emphasized, “Exercise remains beneficial even in polluted environments. But improving air quality can substantially enhance these health gains.”

UCL co-author Professor Andrew Steptoe added, “Toxic air can partially block exercise benefits, though it does not eliminate them entirely. This underscores the importance of addressing fine particle pollution to support healthy ageing alongside physical activity.”

The research combined findings from seven studies, including three unpublished ones, and re-analysed raw participant-level data from three studies. The overall analysis revealed that individuals who engaged in at least 2.5 hours of moderate to vigorous exercise weekly had a 30% lower risk of mortality compared to those who did not meet this threshold.

However, for participants in high PM2.5 areas (above 25 µg/m³), the risk reduction fell to 12–15%. At levels above 35 µg/m³, exercise benefits weakened further, particularly regarding cancer mortality. Around 36% of the global population live in regions exceeding this higher threshold.

In the UK, average yearly PM2.5 levels were about 10 µg/m³, below the critical thresholds, though winter pollution spikes in some cities can surpass 25 µg/m³.

Professor Paola Zaninotto of UCL advised, “We don’t want to discourage outdoor exercise. Checking air quality, choosing cleaner routes, or reducing intensity on polluted days can help maintain exercise benefits.”

The authors noted that the study was mostly conducted in high-income countries, so results may differ in low-income regions with higher pollution levels, often exceeding 50 µg/m³. Limitations also included limited data on indoor air quality and participants’ diets.

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Other factors such as income, education, smoking habits, and pre-existing chronic diseases were accounted for in the analysis.