Air pollution can significantly undermine the health benefits of regular exercise, according to a new global study.
An international team, including researchers from University College London (UCL), analysed data from over 1.5 million adults tracked for more than a decade across countries including the UK, United States, Taiwan, China and Denmark.
The findings, published in the journal BMC Medicine, suggest that while exercise remains beneficial, long-term exposure to fine particulate air pollution – known as PM2.5 – weakens its protective effect, particularly for people living in more polluted areas.
These fine particles, smaller than 2.5 micrometres, are inhaled deep into the lungs and enter the bloodstream.
The researchers found that when annual average PM2.5 levels reached 25 micrograms per cubic metre or higher, the health benefits of physical activity began to diminish. This threshold is exceeded in areas where nearly half of the world’s population live, the researchers noted.
Air pollution and exercise benefits
People who met the standard weekly exercise guideline – at least two and a half hours of moderate to vigorous activity – were found to have a 30% lower risk of dying during the study period compared with less active individuals.
However, among those living in areas with PM2.5 levels above 25 micrograms per cubic metre, this risk reduction was halved, to 12-15%. At even higher pollution levels above 35 micrograms per cubic metre, benefits against cancer-related death were no longer statistically robust.
In the UK, the study reported an average PM2.5 level of 10 micrograms per cubic metre, below the thresholds identified. However, pollution spikes – particularly in urban areas during winter – can exceed the 25 micrograms per cubic metre level, the researchers said.
Co-author Professor Andrew Steptoe, professor of psychology and epidemiology and head of the Research Department of Behavioural Science and Health at UCL, commented: ‘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 ageing and so we encourage greater efforts to curb health-harming pollution levels.’
Co-author Professor Paola Zaninotto, professor of medical and social statistics in UCL’s Department of Epidemiology & Public Health, added that people must not be discouraged from exercising outdoors, but they should be advised to check air quality, choose cleaner routes and ease off exercise intensity on more polluted days in order to get the most health benefits from exercise.
A version of this article was originally published by our sister publication Nursing in Practice.