Bike Sharing Benefits and Risks Differ by Age, Gender

Medical Interview with:
James Woodcock
Senior Research Associate
UK CRC Centre for Diet and Activity Research
MRC Epidemiology Unit, University of Cambridge What are the main findings of the study?

Dr. Woodcock: The cycle hire scheme in London has benefited health through increasing physical activity. This reduces risk from a range of diseases including heart disease, type 2 diabetes, and depression. These benefits were at a population level bigger than the harms the cyclists faced from injury risk or air pollution exposure.  Looking at the harms air pollution did not make much difference.  The injury risk for users of the hire bikes appears to not be higher and may be lower than that for general cycling in the same area. However, the injury risks for general cycling in the cycle hire zone were quite high and benefits for cyclists would be greater if these risks were reduced. When we broke results for general cycling in the area down by age & gender we found two interesting findings. Firstly, that the risks faced by women were higher than for men and so benefits were less clear. Secondly, when we looked at results by age group the trade-off improved very considerably as people got older and for younger people (under 30) there may actually be harms. Were any of the findings unexpected?

Dr. Woodcock: Previously only one study, of which we are aware, has looked at the risk for cyclists by age and this was for the low risk environment of the Netherlands and only looked at mortality. Our finding that the benefits from being active are much larger for middle aged and older people than for younger people are not surprising if one considers that most of the diseases affected by physical activity are not in the main affecting young people (apart from depression). However, previous work has not explored this issue. Injury risks also increase with age so understanding how both benefits and harms increase but the benefits much faster than the harms is an interesting finding. Perhaps most surprising is that the injury risks could probably be reduced so that even in the under 30s there is a positive health trade-off. Of course if being active when you are young builds habits that keep you active as you get older then the benefits will be much larger. We also did not model lags between activity and health outcomes, which again could improve the story for younger people.

Dr. Woodcock: What should clinicians and patients take away from your report? That achieving the full potential benefits from cycling requires getting people who are middle-aged to older cycling and that there are big differences in injury risk between settings and so it should be possible to reduce the risks cyclists face. Benefits would also be larger if less active people got cycling. Based on data on existing cyclists we assumed that the additional cyclists were already more active than the average person.  What recommendations do you have for future research as a result of this study?

Dr. Woodcock: Our uncertainty analysis shows which uncertainties make the biggest difference to final results and issues like the shape of the dose response curve for physical activity make a big difference. As more data come out it will be possible to confirm if the hire bike users are at lower risk and if so why this might be. Perhaps the priority though should be research that understands how we can make cycling a normal choice across the life course and so achieve the potential benefits.


Health effects of the London bicycle sharing system: health impact modelling study

Last Updated on February 14, 2014 by Marie Benz MD FAAD