A new study has found the health effects of cycling outweigh the negative effects of air pollution even in cities with very poor air quality, such as London and Delhi – but its authors warn bike messengers could be the exception due to their level of exposure.
For the first time scientists at the University of Cambridge and the University of East Anglia, have modelled the risks and benefits of walking and cycling in varying levels of air pollution around the world, using computer simulations from epidemiological studies and meta-analyses data.
While previous studies have shown the benefits of exercise in polluted environments this research suggests in only the worst 1% of polluted cities the ill effects of poor air quality outweigh the benefits of exercise. However, for bike messengers the health benefits of cycling may be cancelled out by exposure to air pollution because they spend long periods in areas of poor air quality, while the health benefits of active travel in polluted areas are less marked in fitter individuals.
Dr Marko Tainio, from the MRC Epidemiology Unit at the University of Cambridge, who led the study, says: “Our model indicates that in London health benefits of active travel always outweigh the risk from pollution. 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.
He said: “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.”
The study was led by researchers from the Centre for Diet and Activity Research (CEDAR), a partnership between the Universities of Cambridge and East Anglia.
Senior author Dr James Woodcock, also from CEDAR, says the results make the argument for investment in infrastructure to encourage cycling and walking.
“Whilst this research demonstrates the benefits of physical activity in spite of air quality, it is not an argument for inaction in combatting pollution. It 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.”
The authors say their model doesn’t take into account detailed information on short-term air pollution spikes, or on conditions within different localities in cities, or on individuals’ physical activity and disease history. They add for fitter individuals the benefits of active travel will be smaller than those who are less active outside their commute.
To find out more about the study, and the University of East Anglia's research, click here.