Regular exercise is good for your health, but filthy air can take some of the shine off. A large international study has found that long-term exposure to fine particle pollution can weaken the life-extending benefits of being physically active.
The message is not to stop exercising outdoors. Instead, it highlights why clean air and physical activity need to go hand in hand.
What the researchers looked at
Researchers brought together data from seven long-term studies that followed more than 1.5 million adults for over ten years.
Participants lived in several countries, including the UK, Taiwan, China, Denmark and the United States.
They looked at:
- How active people were in their leisure time
- Long-term exposure to fine particle pollution (PM2.5) where they lived
- Deaths from any cause, cancer and cardiovascular disease
Across all studies, people who managed at least two and a half hours of moderate or vigorous exercise a week had about a 30% lower risk of dying during the follow-up period compared with those who were less active.
Where air pollution starts to change the picture
The team focused on PM2.5 – very small particles less than 2.5 micrometres in diameter that can penetrate deep into the lungs and enter the bloodstream.
They found:
- When annual average PM2.5 levels were below 25 micrograms per cubic metre (μg/m³), exercise gave the full protective effect
- When PM2.5 was 25 μg/m³ or higher, the benefit of exercise dropped sharply
- At these higher pollution levels, the risk reduction from high levels of activity fell to around 12–15%
At very high pollution levels (above 35 μg/m³), the gains from exercise weakened further, particularly for cancer-related deaths.
Around a third of the global population lives in areas with PM2.5 above this level.
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What about the UK
In this analysis, people in the UK were typically exposed to average PM2.5 levels of about 10 μg/m³, which is below the threshold where exercise benefits were significantly blunted.
But that is only part of the story. Air pollution in UK towns and cities varies a lot over the year.
Winter spikes, traffic hotspots and local industry can push levels above 25 μg/m³, at least for short periods.
Should you stop exercising outdoors
No. The authors are clear that exercise remains beneficial, even in polluted areas. However, the dirtier the air, the smaller the payoff.
Simple steps that may help:
- Check local air quality forecasts when you can
- Choose quieter, greener routes away from main roads
- Avoid the most polluted times of day when possible, such as rush hour
- Dial down intensity on the worst days and exercise indoors instead
Limitations worth noting
Most of the data came from high-income countries, so the results may not fully reflect conditions in places where pollution is far worse, sometimes above 50 μg/m³.
The studies also could not fully account for indoor air quality or people’s diets.
However, the analyses did adjust for a wide range of other factors, including income, education, smoking and existing long-term conditions.
The take home message is:
- Moving your body still matters, even if you live in a polluted area
- Long-term exposure to fine particle pollution can erode some of the benefits of exercise
- Cleaning up the air could unlock much greater health gains from the effort people already put into being active
Study: Ku P-W et al. BMC Medicine 2025.
