Not good for your health Panoramic Images/Getty

Is exercise always good for you, even in the smog? In cities as badly polluted as Delhi, it depends how long you do it for.

We are often told that walking and cycling is good for your health. But many people can be put off exercising outside because of air pollution, which has been linked with heart disease and lung cancer – especially as breathing harder means more dirty air passes through your lungs.

Now a study has weighed the benefits of exercise against the damage that can be caused by air pollution. While cycling and walking are always the best options for your health in most cities, including London, this wasn’t the case for Delhi in India, Karachi in Pakistan and Doha in Qatar, which are some of the most polluted cities in the world.


“Pollution causes thousands of deaths a year,” says James Woodcock at the University of Cambridge. His team has combined data on the effects of exercise on life expectancy with pollution readings from cities all over the world.

They found that in Delhi, the benefits of cycling outweigh the harms from smog only if you ride your bike for five hours or less a week. That means if your daily commute is more than half an hour each way, cycling in Delhi’s air pollution – which is the worst in the world – is doing you more harm than good.

People who cycle for many hours a day, such as bike couriers, will experience even more harm from the smog.

Journal reference: Preventive Medicine, DOI: 10.1016/j.ypmed.2016.02.002