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A recent study found a link between the number of sexual partners a man has had in his lifetime and prostate cancer risk.

The study conducted by researchers from the University of Montreal yielded conclusive yet varying findings based on the subjects' "sexual orientation".

For heterosexual men who've had slept with 20 or more women in their lifetime, the chances of developing prostate cancer lowered by as much as 28 per cent. Their risk of developing the most aggressive types of cancer likewise decreased by 19 per cent.

However, the study also discovered that men who had never had sex were almost twice as likely to get prostate cancer compared to those with "active" sex life (with women).

The quantity of sexual partners vis-à-vis prostate cancer risk yielded quite the opposite findings for gay men, with a reported doubled risk of having the said disease for those who had sex with more than 20 men. Their risk of developing a less aggressive prostate cancer also increased by a whopping 500 per cent compared with monogamous gay men, the researchers said.

The study involved 3208 men who were surveyed on their lifestyle, and sexual experiences and practices. Of these participants, 1590 were diagnosed with prostate cancer between September 2005 and August 2009, while 1618 men were part of the control group.

It revealed that men who developed prostate cancer were twice as likely to have a relative with prostate cancer, but what astonished the researchers more was the link between frequency of sexual intercourse with different partners and prostate cancer.

As for the possible scientific basis of the findings, Marie-Elise Parent, one of the study's authors, suggested that heterosexual men have more ejaculations, which previous studies attribute to a lower concentration of carcinogenic crystal-like substances in the fluid of the prostate.

"It is possible that having many female sexual partners results in a higher frequency of ejaculations, whose protective effect against prostate cancer has been previously observed," Parent said.

For homosexual men, the researchers speculated that higher prostate cancer risk followed the increased risk of acquiring sexually transmitted diseases, and the damage caused to their bodies from anal intercourse.

Parent said that she could only formulate "highly speculative" hypotheses to explain the association.

The research, published in the journal Cancer Epidemiology, is the first of its kind to make a link between the number of sexual partners and the risk of developing cancer.

"We were fortunate to have participants from Montreal who were comfortable talking about their sexuality," Parent said. "This openness would probably not have been the same 20 or 30 years ago. We now know that the number and type of partners must be taken into account to better understand the causes of prostate cancer," she added.

Parent was mum, though, when asked whether public health authorities should recommend men to sleep with many women in their lives, saying "We're not there yet".