Long-term exposure to toxic air can substantially weaken the health benefits of regular exercise, suggests a new study conducted by an international team including researchers from University College London (UCL). The study, published in the journal BMC Medicine, analyzed data from over 1.5 million adults tracked for more than a decade across countries such as the UK, Taiwan, China, Denmark, and the United States.
The research indicates that while regular exercise typically reduces the risk of death from any cause, including cancer and heart disease, this protective effect is diminished for individuals residing in areas with high levels of air pollution. The findings highlight the complex interplay between environmental factors and physical health.
Understanding Air Pollution’s Impact
The study focused on fine particulate matter, known as PM2.5, which consists of tiny particles with a diameter of less than 2.5 micrometers. These particles are small enough to penetrate the lungs and enter the bloodstream, posing significant health risks.
According to the research, the health benefits of exercise are notably weakened in areas where the annual average level of PM2.5 reaches 25 micrograms per cubic meter (μg/m³) or higher. Alarmingly, nearly half of the global population lives in regions exceeding this pollution threshold.
“Our findings emphasize that exercise remains beneficial even in polluted environments. However, improving air quality can greatly enhance these health gains,” stated Professor Po-Wen Ku of National Chung Hsing University, Taiwan.
Global and Local Perspectives
Co-author Professor Andrew Steptoe from UCL’s Department of Behavioural Science & Health commented on the broader implications of the study. “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,” he noted.
The research team conducted a comprehensive analysis by combining data from seven existing studies, including three unpublished ones. They re-analyzed raw data for three studies at the individual participant level to ensure robust conclusions.
By the Numbers: People who engaged in at least two and a half hours of moderate or vigorous exercise weekly had a 30% lower risk of dying during the study period. However, in high pollution areas, this risk reduction dropped to 12-15%.
Implications for Public Health
At pollution levels above 35 μg/m³, the benefits of exercise further diminished, particularly concerning cancer mortality, where the protective effects were no longer significant. This is a pressing issue as approximately 36% of the world’s population resides in areas exceeding this level of fine particle pollution.
In the UK, average annual PM2.5 levels are lower, around 10 μg/m³. However, pollution spikes, particularly during winter, often exceed the critical 25 μg/m³ threshold identified in the study.
“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,” advised Co-author Professor Paola Zaninotto from UCL’s Department of Epidemiology & Public Health.
Challenges and Future Directions
The study’s authors acknowledge several limitations, including its focus on high-income countries, which may not reflect conditions in low-income regions where pollution levels often surpass 50 μg/m³. Additionally, the study lacked data on indoor air quality and participants’ diets, although it did account for factors such as income, education, smoking habits, and existing chronic diseases.
The research, involving experts from the UK, the United States, Australia, and Asia, utilized data from the UK Biobank for its UK segment. Funding support came from Taiwan’s National Science and Technology Council, Taichung Veterans General Hospital, and National Chung Hsing University.
As the world grapples with both pollution and sedentary lifestyles, this study underscores the urgent need for policies that address air quality while promoting physical activity. The findings call for a dual approach to public health: promoting exercise and improving environmental conditions to maximize health benefits.
