A study has pointed out that it is healthier to ride a cycle than to drive, despite the many risks urban cyclists face.
The study also showed that the health of the individual cyclists may improve as they drive less and exercise more, and the resulting reduction in exhaust emissions will benefit the entire community.
"The promotion of walking and cycling is a promising way to increase physical activity across the population by integrating it into daily life," state the study authors.
However, they note that if cycling is to be promoted for health reasons, the health benefits of cycling should outweigh the risks.
Studies in Denmark, Finland, and China have shown that cycling is healthier than driving, but these studies have not tried to quantify specific health risks and benefits related to cycling, making it difficult to extrapolate results to specific environments and populations.
To develop an integrated assessment of the health risks and benefits of cycling, the researchers analysed data from international studies on exposure to components of automobile exhaust, traffic fatalities, and benefits of exercise.
For their analysis, the authors estimated the health impacts if 500,000 Dutch people aged 18-64 years were to switch from driving to cycling for one round trip of 7.5-15 km each day.
They chose to estimate health in terms of mortality (years of life gained or lost) rather than morbidity (illness) because data about mortality tend to be more consistent; for example, minor traffic accidents involving cyclists tend to be far underreported compared with traffic deaths.
The authors found that cycling even short times in traffic can cause significant exposure to components of car exhaust, including ultra fine particles and soot, which can contribute to respiratory and cardiac illness.
Cyclists are also more vulnerable to fatal traffic accidents than drivers, even in the Netherlands, which has a strong cycling culture and infrastructure, including dedicated bike trails.
The authors estimated that in the Netherlands, the risk of dying in a traffic accident is four times greater per kilometre travelled for cyclists than for drivers.
The risk ratios vary by age, because younger drivers are far more likely to die in traffic accidents than older drivers, so their risk of death might actually decrease if they switch to cycling.
Health benefits from cycling may also vary by the age. For example, older, sedentary adults tend to benefit most from increased exercise.
However, benefits of exercise can be substantial for persons of all ages; some researchers estimate that inactive individuals who begin moderate exercise programs can lower their risk of death from all causes by 10 percent to 50 percent.
The community health benefits are also greater than the risks to the individual cyclists, primarily because eliminating 500,000 car trips per day would reduce air pollution.
In countries like the United Kingdom, which has a higher rate of traffic fatalities among cyclists, the researchers estimated that benefits of cycling would still be seven times greater than the risks.
The health benefits of cycling may be less in some developing countries where cyclists may face higher levels of pollution and higher risks in traffic, according to the researchers.
Nevertheless, they state that their results are part of a growing body of research that supports the public health benefits of walking and cycling for transportation.
The study has been published online in the peer-reviewed journal Environmental Health Perspectives (EHP).