Cycling in cities with heavy air pollution still good for health: study

The health benefits of walking and cycling outweigh the harm on health from air pollution, even in cities with high levels of air pollution, according to a study published online Thursday in the journal Preventive Medicine.

Air pollution is one of the leading environmental risk factors for people's health. One of the main sources of air pollution in cities is transport and a shift from cars, motorbikes and buses to active travel, such as walking and cycling, would help to reduce emissions. However, people who walk or cycle in such environments will inhale more pollution, which could be detrimental to their health.

Previous studies conducted in Europe, the United States and several other developed countries found that the health benefits of active travel are greater than the risks, but these were undertaken in areas of relatively low air pollution, and the applicability of their results to more polluted cities in emerging economies has been uncertain.

The new study led by researchers from the University of Cambridge used 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, using information from international epidemiological studies and meta-analyses.

Using the data, the researchers calculated that in practical terms, air pollution risks will not negate the health benefits of active travel in the vast majority of urban areas worldwide.

Only one percent of cities in the World Health Organization'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, according to the study.

"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," said Dr Marko Tainio from the University of Cambridge, who led the study.

But 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, said Tainio.

This research provides further support for investment in infrastructure to get people out of their cars and onto their feet or their bikes, which can itself reduce pollution levels at the same time as supporting physical activity, according to the researchers. Endit