Lotharios lower risk of prostate cancer

Sleeping with more than 20 women protects men against prostate cancer, a study has suggested.

Men who had slept with more than 20 women lowered their risk of developing the cancer by almost a third, and were 19% less likely to develop the most aggressive form.

In contrast, men who slept with 20 other men doubled their risk of developing prostate cancer compared with men who had never had sex with another man.

Researchers at the University of Montreal believe that intercourse protects men, and men who are more promiscuous have more sex than those in monogamous relationships.

But for homosexual men the benefit is lost because of the increased risk of picking up a sexually transmitted disease, and the physical damage caused by such intercourse.

However, gay men with only one partner were said to be at no greater risk.

"It is possible that having many female sex partners results in a higher frequency of ejaculations, whose protective effect against prostate cancer has been previously observed in cohort studies," said the study's lead researcher, Marie-Elise Parent.

But when asked whether public health authorities should recommend that men sleep with lots of women, Parent prevaricated: "We're not there yet."

The study looked at more than 3200 men over the four years from 2005 to 2009.

Overall, men with prostate cancer were twice as likely to have a relative with cancer. But the researchers were surprised to find that the number of sexual partners also affected the development of the cancer.

Men who said they had never had sexual intercourse were almost twice as likely to be diagnosed with prostate cancer.

When a man has slept with more than 20 women during his lifetime there was a 28% reduction in the risk of getting prostate cancer, and a 19% reduction for the aggressive types of the cancer.

Previous studies have found that sexual intercourse may protect against prostate cancer because it reduces the concentration of carcinogenic crystal-like substances in the fluid of the prostate.

But the new study, published in the Journal of Cancer Epidemiology, is the first to link sexual frequency with the risk of developing cancer.

"We were fortunate to have participants from Montreal who were comfortable talking about their sexuality, no matter what sexual experiences they have had," said Parent.