Regular physical activity is widely recognised as a key factor in lowering the risk of chronic illness and early death, but new research suggests that polluted air can weaken some of those protective effects. A large international study has found that the health gains from exercise decline as neighbourhood air pollution levels rise, particularly for heart disease and cancer.
The research, published in the journal BMC Medicine, examined data from more than 1.5 million adults across the United Kingdom, Denmark, the United States, Taiwan, and China. Participants were tracked for over a decade, allowing researchers to assess long-term patterns in physical activity, pollution exposure, and mortality.
The study focused on fine particulate matter, known as PM2.5, a hazardous pollutant produced by vehicle emissions, the burning of coal and other fuels, waste incineration, and several industrial activities. These particles are small enough to enter the bloodstream and affect organs, including the heart and lungs.
According to the analysis, people who engaged in at least two and a half hours of moderate or vigorous exercise each week had a 30 percent lower risk of death compared with those who were less active. But this advantage declined sharply for individuals living in areas where PM2.5 levels exceeded 25 micrograms per cubic metre. In such neighbourhoods, the risk reduction dropped to between 12 and 15 percent. The protective effect eroded even further in regions with PM2.5 concentrations above 35 micrograms per cubic metre — levels that affect more than a third of the world’s population.
Andrew Steptoe, a professor of psychology and epidemiology at University College London and one of the study’s authors, said the findings highlight the growing threat posed by fine particle pollution. “Toxic air can, to some extent, block the benefits of exercise, although not eliminate them,” he said. He noted that the results add to a growing body of evidence showing the widespread harm caused by PM2.5 exposure.
The study also points to several limitations. Much of the data came from high-income countries, which tend to have stronger pollution controls than low-income regions. The researchers did not have detailed information on indoor air quality or diet, two factors that could influence long-term health outcomes. Still, the findings remained consistent after adjustments for income, education, smoking, and underlying medical conditions.
The authors stressed that people should not avoid outdoor exercise. Paola Zaninotto, another UCL researcher involved in the project, said that small changes can help reduce exposure. Choosing cleaner routes, monitoring local air quality, or reducing workout intensity on high-pollution days may help maintain the benefits of regular activity.
The study adds to growing calls for stronger global efforts to reduce air pollution. Steptoe said both clean air and physical activity play an important role in healthy ageing, and urged governments to prioritise measures that reduce harmful emissions.
