Air pollution may cut into health benefits from exercise, study finds

The health benefits of regular exercise fall sharply in neighbourhoods with dirty air, a new analysis suggests.

People who work out frequently have a lower risk of death overall. But exposure to high levels of air pollution can cut into that protection over time, particularly for cancer and heart disease, according to the study, which was published in the journal BMC Medicine.

The findings indicate that physical activity is good for people’s health even in polluted areas – but that boosting air quality could maximise these gains, the researchers said.

“Our study shows that toxic air can, to some extent, block the benefits of exercise, although not eliminate them,” said Andrew Steptoe, one of the study’s authors and a psychology and epidemiology professor at University College London (UCL).

“The findings are further evidence of the damage that fine particle pollution can do to our health,” he added in a statement.

Steptoe’s team analysed data from more than 1.5 million adults who were tracked for more than 10 years in the United Kingdom, Denmark, the United States, Taiwan, and China.

The researchers focused on a type of air pollution known as fine particulate matter, or PM2.5. These particles – which come from burning coal and other fossil fuels, vehicle emissions, burning waste, and other sources – are so tiny they can cross the blood-brain barrier and affect the heart and lungs.

People who did at least 2.5 hours of moderate or vigorous exercise per week had a 30 per cent lower chance of dying during the study period compared with people who worked out less often.

But if they lived in an area with air pollution levels above 25 micrograms per cubic meter of air (μg/m³), the risk reduction for highly active people fell to 12 per cent to 15 per cent, according to the study.

The protective benefits of exercise wore off even further at higher pollution levels, above 35 μg/m³ – a threshold where 36 per cent of the global population lives, the study said.

Other research has linked air pollution to respiratory and heart diseases as well as neurological disorders such as Parkinson’s disease and dementia.

“We don’t want to discourage people from exercising outdoors,” said Paola Zaninotto, one of the study’s authors and a professor of medical and social statistics at UCL.

“Checking air quality, choosing cleaner routes, or easing off intensity on polluted days can help you get the most health benefits from your exercise,” she added.

The study has some limitations, notably that most of the analysis was conducted in wealthy countries. That means the findings may not apply to lower-income regions where air pollution is even higher.

The researchers also did not have data on indoor air quality or people’s diets, which could also skew the findings. However, the results held even after they took into account factors such as income, education, smoking, and health status.

Overall, the researchers said the findings support efforts to clean up dirty air worldwide.

“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,” Steptoe said.