Regular readers of Obesity Panacea will know that I am a huge fan of active transportation, which entails commuting via active means (e.g. walking, cycling, or taking public transit) rather than driving. But when I talk with my friends about the many health and societal benefits of active commuting by bicycle, they almost always bring up the fact that they value their lives too much to risk cycling on busy city streets. This is obviously not a trivial concern – here in Ottawa there were three cycling deaths in a three day period in August, and another tragic death occurred earlier this week (although in at least 2 of those accidents, it may have been cyclist errors which resulted in the accidents).
So I was extremely interested when I came across a recent paper in Environmental Health Perspectives which examines whether the benefits of increased cycling (increased physical activity) outweigh the risks (both in terms of accidents and exposure to pollutants for individual cyclists). To calculate these numbers, the authors examine changes in mortality at both the population level, and for individual cyclists, if 12.5% of current short car trips in the Netherlands were to be performed by cycling instead.
So, what did they find?
The authors report that for most adults, the risk of death when cycling is about 4.3x higher than if the same trip were being made by car (YIKES!). However, we’ve got to remember that commuters not only pose a risk to themselves – they also post a risk to other road users. And if you’re going to be hit by a vehicle, a Cervelo is going to do you a lot less harm than a Corolla! So with an increase in the number of trips made by bike, the increased mortality among cyclists due to traffic accidents is offset by the reduced mortality among the general population who would be less likely to be run over crossing the street (interestingly, if it were high risk young drivers who were to switch from driving to cycling, it would actually save lives!).
Now while the risk of being in an accident is higher for cyclists, it must be remembered that they are also likely to be getting increased levels of health promoting physical activity, and substantially reducing their volume of sedentary time. In fact, the risk of death due to physical inactivity among active commuters is estimated to be 10-50% lower than in non-active commuters – a pretty substantial health benefit!
So will cycling to work make your life longer or shorter? On average, the risk due to car accidents will reduce your life expectancy by just 5-9 days. Being exposed to air pollution during your commute could cost you another 8-40 days. But the physical activity in your commute would actually increase your life expectancy by up to 14 months! Overall, the health benefits of active commuting by bike are 9 times greater than the risks!
What’s the take-home message?
Cycling is obviously more dangerous that it should be, something which needs desperately to be addressed. But if you decide to commute by bicycle on a regular basis, you are far more likely to improve your health and prolong your life via increased physical activity than you are to shorten your life by getting involved in an accident. Interestingly, the number of cyclists on the road is inversely related to the number of cycling deaths – so the more of us that get out on the roads, the less likely we are to get in an accident.
And if you do choose to cycle more regularly (which I definitely think you should!), please wear a helmet and obey traffic laws – especially stop signs. Those two factors alone will go a long way to preventing cycling related deaths.
Johan de Hartog J, Boogaard H, Nijland H, & Hoek G (2010). Do the health benefits of cycling outweigh the risks? Environmental health perspectives, 118 (8), 1109-16 PMID: 20587380