A team of scientists in England have found that even in many of the most polluted cities in the world, cycling or walking outdoors is not significantly damaging to peoples' health.
“The good news is that across the world, in 99% of cities it is safe to cycle up to two hours a day,” Dr. Audrey de Nazelle from the centre for environmental policy at Imperial College London, told the Guardian.
The study weighed the risks of breathing in polluted air against the benefits of daily exercise like walking or biking. It found that in most places, including heavily polluted cities like New Delhi, exercising still outweighed the negative health effects of the pollution. In each city, the researchers came up with a "tipping point," a number of minutes of exposure at which the harmful effects of the pollution begin to outweigh the benefits from exercising.
“Even in Delhi, one of the most polluted cities in the world–with pollution levels ten times those in London–people would need to cycle over five hours per week before the pollution risks outweigh the health benefits," Dr. Marko Tainio from the Cambridge MRC epidemiology department told the newspaper.
Researchers said the study doesn't mean that the pollution levels in these cities can't do any harm or that pollution shouldn't be dealt with as a serious public health problem, but that it is possible for people to get some exercise despite living in heavily polluted areas.
“That’s because physical inactivity is such a public health issue–it is not that pollution is not detrimental,” said Nazelle.