Healthcare (Commonwealth Union) – The long-term exposure to polluted air may greatly lower the positive health effects of regular physical activity, as demonstrated in a new study conducted by an international research group that includes scientists from the University College London (UCL).
The research, published in BMC Medicine, examined data from over 1.5 million adults who were followed for more than ten years across the UK, Taiwan, China, Denmark, and the United States.
The scientists of the study noted that while exercise normally brings down the risk of death from any cause—including cancer and cardiovascular disease—this protective benefit was noticeably weakened, though not completely eliminated, among people living in areas with high air pollution.
The team focused on concentrations of fine particulate matter, known as PM2.5—microscopic particles less than 2.5 micrometres wide that can lodge deep in the lungs and enter the bloodstream.
They found that the advantages of regular exercise dropped substantially when annual PM2.5 levels reached 25 micrograms per cubic metre (μg/m³) or higher. Nearly half of the global population (46%) lives in regions where pollution surpasses this level.
The study’s lead author, Professor Po-Wen Ku from National Chung Hsing University in Taiwan, indicated that their results highlight that physical activity is still good for us, even when the air is polluted. But cleaner air can significantly boost these positive effects.
Co-author Professor Andrew Steptoe, from UCL’s Department of Behavioural Science & Health, indicated that they found that polluted air can partly reduce the advantages of exercising, though it does not wipe them out entirely. These results add to the growing body of evidence showing how harmful fine particulate pollution is to human health.
He further indicated that they think that both fresh air and regular movement are crucial for healthy ageing, and therefore stronger action is needed to lower pollution that harms people’s wellbeing.
To conduct the research, the team examined information from seven previous studies — including three that had not yet been published — and merged the key statistics into one combined analysis. For three of those studies, they also went back to the original data and carried out new analyses at the level of individual participants.
Bringing together results from seven separate studies, the researchers found that adults who completed at least two and a half hours of moderate-to-vigorous exercise each week had about a 30% lower chance of dying during the study period compared with those who didn’t reach that level of activity.
But among people in this highly active group who lived in areas with elevated fine-particle pollution (over 25 μg/m³), this reduction in risk dropped to around 12–15%.
When pollution levels rose even further — above 35 μg/m³ — the positive effects of exercise weakened more noticeably. This was especially true for cancer-related deaths, where the protective impact of physical activity was no longer strong. Roughly one-third of the global population (36%) live in regions where annual PM2.5 levels surpass 35 μg/m³.
In the UK, average annual PM2.5 concentrations for study participants were below these limits, at around 10 μg/m³. Even so, fine-particle pollution can fluctuate significantly, and pollution surges in UK cities do occasionally exceed 25 μg/m³ — the key threshold highlighted in the study — particularly during winter.
The co-author Professor Paola Zaninotto, from UCL’s Department of Epidemiology & Public Health, says “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.”
In discussing the study’s limitations, the researchers pointed out that most of the data came from high-income nations, meaning the results may not fully reflect conditions in lower-income regions where fine particle pollution often surpasses 50 μg/m³. They also highlighted gaps such as the absence of information on indoor air quality and participants’ dietary habits.
