Relax, Cycling Probably Won’t Give You Cancer

Repeat after me: Relative risk is not the same as absolute risk.

Mail Online has published a story linking cycling to an increased risk of prostate cancer.

It’s based on a study published in the Journal of Men’s Health.

The researchers found the first evidence of a link between cycling and prostate cancer. They conclude that the association “warrants further investigation” and are keen to stress that the finding is preliminary.

Though Mail Online says the finding doesn’t “necessarily prove” cycling causes cancer, it does say:

…the statistical link with prostate cancer could create a new, and unexpected, health concern for the millions of men who regularly cycle.

Should you be worried?

Jean-Paul Pelissier / Reuters

(Tl;dr: No, you should not be worried.)

1. First, it’s important to remember that relative risk is not the same as absolute risk.

Absolute risk tells you the overall chance of something happening. Relative risk compares the chance of something happening to one group versus another group.

For example, say there’s a 0.1% chance of it raining today. If you say that it’s nine times as likely to rain tomorrow, that sounds like a huge increase. But when you do the maths the chance of rain tomorrow is still only 0.9%.

Cancer Research UK has a good explanation of how the media often skews statistics in cancer stories.

2. So a sixfold increase in the risk of prostate cancer in cyclists is not the huge jump it initially sounded like.

The actual numbers in the study were as follows: three out of 511 men who cycled for less than 3.75 hours a week had been diagnosed with prostate cancer, as did 17 out of 498 men who cycled more than 8.5 hours a week.

That’s an absolute increase from 0.6% to 3.4%.

4. Moreover, the lead author of the paper, Dr Mark Hamer, told BuzzFeed in an email that there’s not yet enough evidence to draw conclusions.

We simply cannot go around saying cycling is ‘causing’ prostate cancer based on cross sectional evidence. Far more detailed work is needed using prospective study designs and RCT [randomised control trial] approaches to draw any firm conclusions.

5. The benefits of cycling are still much greater than any risks. Hamer says:

The overall health benefits associated with cycling/exercise (reduced cardiovascular disease, diabetes, etc.) far outweigh any risks.

6. So don’t give up on cycling yet.

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Kelly Oakes is science editor for BuzzFeed and is based in London.
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