A new large-scale international study has confirmed that regular physical activity significantly reduces the risk of premature death, but heavy air pollution weakens this positive effect, particularly in terms of protection against cancer and heart diseases.
The research, published in the journal BMC Medicine, relied on data from over 1.5 million adults collected over more than 10 years from countries including the US, Denmark, the UK, China, and Taiwan.
The scientists focused on fine particulate matter in the air, 2.5, which have a diameter of less than $2.5$ micrometers and can pass into the bloodstream after reaching the lungs.
The group concluded that the beneficial health effect of exercise was significantly reduced where the average annual level of PM2.5 reached or exceeded 25 micrograms per cubic meter. Nearly half of the world’s population (6%) lives in conditions exceeding this threshold.
By pooling the data, the scientists determined:
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People who exercised for at least two and a half hours a week at moderate or high intensity had a 30% lower risk of premature death compared to inactive individuals.
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However, if these active people lived in a high-pollution zone, the positive effect was halved, amounting to 12%–15%.
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In the highest-pollution zones, the benefits of exercise were further attenuated, particularly concerning the risk of death from cancer.
The study authors note that their goal is not to discourage people from exercising outdoors. Instead, they recommend checking air quality before starting a workout, choosing less polluted routes for running or walking, and, most importantly, reducing exercise intensity on days when air pollution levels are high.
