Middle aged men who spend nine hours a week on their bike are more likely to be diagnosed with prostate cancer, new research suggests.
A British study of 5,200 cyclists is the biggest research project ever conducted on the health impact of cycling.
It suggests that cyclists in in their 50s who bicycle for more than nine hours a week may be up to five times as likely to receive a diagnosis of prostate cancer.
The team of scientists at University College London, found there was no link between cycling and infertility or erectile problems - an age-old health myth.
But the statistical link with prostate cancer could create a new, and unexpected, health concern for the millions of men who regularly cycle.
The sport has already been linked with testicular cancer, with repeated impacts raising the chance of being diagnosed with the disease. Former cyclist Lance Armstrong was famously treated for testicular cancer.
But the connection to prostate cancer has not been made before.
The team said the statistical link - tested in the 2,000 participants who were over the age of 50 - did not necessarily prove that cycling directly causes prostate cancer.
They said the results were surprising and suggested that men who cycle frequently may be more health conscious, leading to more chance of being diagnosed.
But their research found that cyclists were no more likely to visit their GPs regularly than anyone else.
And they said they could not rule out that the cancer cases were caused by an increased pressure on the prostate.
Cycling has undergone a massive boom in the last decade. Some 600million more miles were cycled in Britain in 2012 than in 1993.
And around 80 per cent of those miles were ridden by men.
Study author Dr Mark Hamer, of the Department of Epidemiology at UCL, said: "These results are not straightforward.
"It may well be these men are more health aware and therefore more likely to get a diagnosis.
"Those who are cycling the most did not make up a huge sample so more research is needed."
- Daily Mail