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Transport / Mass transit

Does cycling increase your risk of prostate cancer?

Any plan to give up scarce urban road space to cyclists will inspire many different opponents, peddling many different stories. This one at least wins points for originality. In its first response to the plan for two huge cross-London cycle routes, the Cyclists in the City blog noted:

“The Motorcycle Action Group has already announced its opposition to cycle tracks and – bizarrely – justifies that by saying they will give cyclists higher rates of prostate cancer. (There are too many levels on which that is simply plain weird.)”

The tweet in question has now been deleted (can’t think why). Oddly enough, though, this isn’t quite as leftfield as it sounds. Over the summer, the (peer-reviewed) Journal of Men’s Health published a study which suggests that any policy which significantly increases cycling rates might do just that.

Researchers at University College London surveyed 5,000 male cyclists online, then ranked them by how much they cycled. They then limited the sample to the 2,027 cyclists over the age of 50 (prime prostate territory), before analysing the correlation with the cancer. 

Of the 498 men who biked for more than 8.5 hours a week, 17 (3.5 per cent) had prostate cancer. Of the 511 who biked for less than 3.75 hours, just three (0.5 per cent) did. Once they’d asdjusted the numbers for various other factors, the researchers calculated that the odds of someone who cycles heavily having prostate cancer were six times greater than those of someone who cycles just a little.

Obvious conclusion: stop cycling, wear padded safety pants, never go outside again.

The offending plan: an artist’s impression of the north-south cycle route at St. George’s Circus, south London. Image: TfL.

Okay, that might be a bit extreme, for a whole swathe of reasons. One is that nine hours is quite a big chunk of the week to spend on a bike: if there is an increased risk, it’s affecting only the hardest of hardcore cyclists. Another is that the group who filled the survey in was self-selecting.

The big one, though, is that all the survey showed is an “association”: correlation is not causation, and there’s nothing to suggest that time in the saddle has caused the prostate cancer. It is possible, albeit unlikely, that it’s the other way round, and somewhere out there there’s one bicycle-mad oncologist suggesting it’s the best way of staying active during treatment. 

Another point to note is that 42 is a very small sample, so these results may be down to pure chance. The survey also found no link between cycling and infertility or erectile dysfunction – which is lovely and all (functional genitals, yay!), but also contradicts previous research findings. That rather calls the results into question. 

Even if being a regular cyclist does marginally increase your risk of prostate cancer, it could still be worth doing: cycling, after all, can lead to weight loss and increased fitness, with all the reductions in heart disease, diabetes and so on that that implies. And – let’s be realistic – prostate cancer probably less of a threat than being crushed by an HGV. Unlike prostate problems, the lorry risk can’t be addressed by changing your saddle.

So, does cycling increase risk of prostate cancer? If you’re a woman, then we feel confident in saying that, no, it does not. If you’re a man – plausibly, but possibly not, and it’s really not worth worrying about.

Now – motorcycling in London. There’s a health risk if ever there was one. I’d avoid that if I were you.
This article is from the CityMetric archive: some formatting and images may not be present.