People who cycle through cities are still doing a big favour to their health, even though there are risks involved, according to a new study from the Netherlands.

The researchers found that, even when air pollution in highly populated urban centres was factored in, people were still healthier if they cycled than if they walked or drove.

They also estimated the health impact from people taking up cycling instead of driving en masse, and found that such a mass movement would have profound implications for people's health.

Since air pollution is higher in some developing countries, and since some countries have more traffic risks than others, the benefits of cycling vary from country to country.

However, studies in Denmark, Finland, and China have all also shown that cycling is healthier than driving.

Such studies have not tried to quantify the risks and benefits of cycling, as the current study authors have tried to do, in order to make a cost-benefit analysis of cycling itself.

For the purposes of the study, the researchers analysed data on automobile exhaust, traffic fatalities, and exercise benefits.

The researchers tried to estimate what would happen if 500,000 Dutch people between the ages of 18 and 64 suddenly switched from driving to cycling and rode, instead, up to 15 kilometres every day.

The researchers based their statistics on mortality, which measures years of life gained or lost, rather than morbidity, which measures illness.

Data about mortality tend to be more consistent than data about morbidity, since deaths from certain causes (such as traffic accidents) are often given undue privilege in scientific literature over deaths from cycling accidents.

In their research, the authors found that people who cycled for short amounts of time in traffic were exposed to components of car exhaust, such as ultrafine particles, which contribute to respiratory and cardiac illness.

They also found that Dutch cyclists were more vulnerable to fatal traffic accidents than drivers, even though the Netherlands has a very developed cycling infrastructure and many dedicated bike trails.

The authors found that, however, both the risk of traffic accidents and the health benefits of cycling varied by age.

In general, young people's risk of dying in traffic accidents is much higher than people who are older, and the same people may actually be less at risk if they switched to cycling.

Older adults who have sedentary lifestyles also tended to benefit the most from increasing their daily exercise.

Based on estimates of traffic deaths and the negative health impact of breathing ultrafine particles and soot, the researchers concluded that cycling was still nine times better for people than driving, in the Netherlands.

According to their estimates, people who cycle in the Netherlands live between three and 14 months longer than their peers, due to the increased physical activity they are getting.

Air pollution exposure added a lifelong risk of up to 40 days of of life lost per person.

The study authors said that they felt policy-makers should promote walking and cycling as a way of increasing people's physical activity.