A Canadian team told the British Medical Journal they had found a possible link.

But experts stress this is not proof that one causes the other and it might be a fluke finding.

The researchers believe oestrogen by-products in the urine of pill-users may be entering food and drinking water.

The hormone is known to feed the growth of certain cancers.

The latest investigation looked at data from 2007 for individual nations and continents worldwide to see if there was any link.

The researchers found a significant association between contraceptive pill use in the population as a whole with both the number of new cases of, and deaths from, prostate cancer.

This link was irrespective of the nation's wealth, suggesting it might not be down to better disease detection in more affluent countries that also tend to have higher rates of oral contraceptive use.

And it was strongest in Europe.

Additionally, they found no link between prostate cancer and other forms of contraception, like the coil, suggesting it is not something that is sexually transmitted or associated with intercourse itself.
'Thought-provoking'

Drs David Margel and Neil Fleshner, from Toronto University, fear that contamination of the food chain with hormones originating from the pill are the likely culprit.
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Comparing the rates of two apparently unrelated issues across countries is a notoriously unreliable way of establishing whether they are truly linked”

Jessica Harris Cancer Research UK

They stress that their work merely suggests a link and is not proof.

"It must be considered hypothesis generating and thought-provoking," they say in their BMJ Open report.

They said more investigations are needed and recommend close monitoring of environmental levels of oral contraceptive by-products or endocrine disruptive compounds (EDCs).

Dr Kate Holmes, of The Prostate Cancer Charity, agreed that more research was warranted.

"While this study raises some interesting questions about the presence of EDCs in the environment, it does not contribute to our overall understanding of the development of prostate cancer."

Jessica Harris, of Cancer Research UK, said uncertainty about the disease remained.

"Comparing the rates of two apparently unrelated issues across countries is a notoriously unreliable way of establishing whether they are truly linked, because so many things vary between different countries that it's impossible to say whether one thing is causing the other.

"It has been difficult to identify factors that affect the risk of prostate cancer, but we know that men are at higher risk as they get older, or if they have a strong family history of breast or prostate cancer. The disease is also more common in black men than white or Asian men."