The benefits of cycling and walking outweigh the negative impact on health from air pollution, researchers say.
Even in cities with high levels of pollution the benefits of physical activity outweigh the harms, according to the University of Cambridge.
Experts from the University's Centre for Diet and Activity Research and Medical Research Council Epidemiology Unit, along with researchers from the University of East Anglia, said regular exercise reduces the risk of diseases such as diabetes, heart disease, and several cancers.
One way to get moving is through "active travel", such as walking or cycling, but concerns have been raised about the impact pollution could have on those exercising in such a way - particularly in urban environments.
Experts used information from epidemiological studies and meta-analyses to create computer simulations to compare the risks and benefits for different levels of intensity and duration of active travel and of air pollution in different locations around the world.
The study, published in Preventive Medicine, concluded that only 1 per cent of cities in the World Health Organisation's Ambient Air Pollution Database had pollution levels high enough that the risks of air pollution could start to overcome the benefits of physical activity after half an hour of cycling every day.
"Our model indicates that in London, health benefits of active travel always outweigh the risk from pollution," said study lead Dr Marko Tainio, from the MRC Epidemiology Unit at the University of Cambridge.
"Even in Delhi, one of the most polluted cities in the world - with pollution levels 10 times those in London - people would need to cycle over five hours per week before the pollution risks outweigh the health benefits.
"We should remember, though, that a small minority of workers in the most polluted cities, such as bike messengers, may be exposed to levels of air pollution high enough to cancel out the health benefits of physical activity."
