Tipping point: revealing the cities where exercise does more harm than good

In at least 15 cities, air pollution has now become so bad that the danger to health of just 30 minutes of cycling each way outweighs the benefits of exercise altogether, according to new research

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Who says exercise is always good for you? Cycling to work in certain highly polluted cities could be more dangerous to your health than not doing it at all, according to researchers.

In cities such as Allahabad in India, or Zabol in Iran, the long-term damage from inhaling fine particulates could outweigh the usual health gains of cycling after just 30 minutes. In Riyadh, Saudi Arabia, this tipping point happens after just 45 minutes a day cycling along busy roads. In Delhi or the Chinese city of Xingtai, meanwhile, residents pass what the researchers call the "breakeven point" after an hour. Other exercise with the same intensity as cycling - such as slow jogging - would have the same effect.