The merits of exercise outweigh the negatives of air pollution, even in highly polluted cities like Delhi, a new international study led by Cambridge University claimed on Thursday.
The new study, published in the journal 'Preventive Medicine', found that evidence suggests that the benefits of exercise, even in an environment filled with noxious gases, outweighs the problems brought on by no exercise at all.
"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," said Dr Marko, Tainio from the Cambridge University's MRC epidemiology unit, who led the study.
"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," he added.
The researchers studied the concentration of fine particulates, measured in micrograms per cubic metre, to gauge the levels of pollution in the air of several major world cities.
They then used data from previous studies to estimate how harmful those levels of pollution would be.
The researchers modelled the effects of cycling and walking at different levels of air pollution and established a tipping point - the length of time after which there was no further health benefit, and a break-even point, when the harm from air pollution began to outweigh the health benefit.
For Delhi, the most polluted city on the World Health Organisation's database, the tipping and break-even points for cycling were 30 and 45 minutes per day respectively, while for walking they were 90 minutes and six hours and 15 minutes respectively.
The authors of the international study, from the UK, Switzerland, Spain and Brazil, insisted that their findings should not be a cause for complacency in tackling air pollution levels.
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