Air pollution may reduce health benefits of exercise - Health - Sports medicine & Kinesiology

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Long-term exposure to toxic air can substantially weaken the health benefits of regular exercise, suggests a new study by an international team including UCL (University College London) researchers.

The study, published in the journal BMC Medicine, analyzed data from more than 1.5 million adults tracked for more than a decade in countries including the U.K., Taiwan, China, Denmark and the United States.

The team found that the protective effect of regular exercise on people's risk of dying over a specific period—from any cause and from cancer and heart disease specifically—appeared to be reduced, but not eliminated, for those who lived in high pollution areas.

The researchers looked at levels of fine particulate matter—tiny particles known as PM_2.5 with a diameter of less than 2.5 micrometers across. These particles are so small they can get stuck in the lungs and enter the bloodstream.

Impact of pollution on exercise benefits

The health benefits of exercise significantly weakened, the team found, where the yearly average level of PM_2.5 was 25 micrograms per cubic meter (μg/m³) or higher. Nearly half (46%) of the world's population live in areas exceeding this threshold.

The 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 Behavioral Science & Health, said, "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."

Study methodology and key findings

For the study, the research team looked at data from seven existing studies, including three that were unpublished, combining the summary statistics from each study into one overall analysis. For three of these studies, they re-analyzed the raw data at the level of individual participants.

Combining the data from seven studies, they found that people who did at least two and a half hours of moderate or vigorous exercise a week had a 30% lower risk of dying during the study period than those who did not meet this exercise threshold.

However, if people in this very physically active group lived in an area with high fine particle pollution (above 25 μg/m³), this reduction in risk halved to 12%–15%.

At higher levels of fine particle pollution, above 35 μg/m³, the benefits of exercise weakened further, particularly for risk of death from cancer, where the benefits were no longer robust. About a third of the world's population (36%) live in areas whose yearly average PM_2.5 levels exceed 35 μg/m³.

For study participants in the U.K., the average yearly PM_2.5 levels were lower than these thresholds, at 10 μg/m³. However, levels of fine particle pollution vary a lot and spikes in pollution in U.K. cities do exceed 25 μg/m³, the critical threshold identified in the study, mainly during the winter months.

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 research team

In their section on limitations, the authors noted that the study was mostly conducted in high-income countries, so the findings might not apply to low-income countries where fine particle pollution is higher, often exceeding 50 μg/m³. Other limitations included a lack of data on indoor air quality as well as participants' diets.

However, a wide variety of other factors were accounted for, including income and education levels, health behaviors such as smoking, and the presence or not of existing chronic diseases.

The study involved researchers from the U.K., the United States, Australia, and Asia. For the U.K. part of the study, the researchers used data from the UK Biobank. 

Provided by University College London 

by University College London

edited by Lisa Lock, reviewed by Robert Egan 

Source: Air pollution may reduce health benefits of exercise