Hidden danger of exercising in polluted city air — and how to avoid it

Regular exercise can still provide significant health benefits even in polluted cities, but choosing where and when to exercise can help reduce exposure to harmful air pollutants, according to a BBC Future report.

Air pollution contains fine particles such as PM2.5, as well as nitrogen dioxide, carbon monoxide, sulphur dioxide and ground-level ozone. PM2.5 particles are small enough to penetrate deep into the lungs and enter the bloodstream, while long-term exposure to air pollution has been linked to cardiovascular and respiratory diseases and other health problems.

Exercise increases the amount of air people breathe in because they breathe faster and more deeply during physical activity. This can mean a greater dose of pollutants entering the lungs, particularly when exercising near busy roads.

However, research suggests that the health benefits of physical activity generally outweigh the risks associated with air pollution. A 2016 modelling study found that the benefits of walking and cycling exceeded the harms caused by polluted air except at exceptionally high pollution levels. A more recent review also found that exercising in polluted environments was associated with a 26% lower mortality risk compared with inactivity, while exercising in cleaner air was associated with a 31% reduction.

The level of pollution still matters. Research involving people walking in London found that those exercising in a park with cleaner air experienced greater improvements in lung and blood vessel function than those walking along a busy road. People with conditions such as asthma, chronic obstructive pulmonary disease or cardiovascular disease may also need to take greater precautions.

Experts recommend several ways to reduce exposure while exercising outdoors. Moving just one or two streets away from heavy traffic can reduce pollution exposure by 20% to 30%, while choosing side streets instead of busy roads can cut exposure by about half, according to research cited by the BBC.

Avoiding rush hour can also help, as stationary traffic can create local pollution hotspots. On hot, sunny afternoons, higher ozone levels can add another risk.

Checking local air-quality levels before exercising can help people decide whether to train outdoors, choose a park or exercise indoors. Experts say that while individual choices can reduce exposure, reducing pollution at its sources through broader environmental policies would have a greater impact.

By Aghakazim Guliyev