TUESDAY, Oct. 28, 2014 (HealthDay News) -- Having sex with more than 20 women might have some risks for men, but a new study suggests it could also have an unexpected health benefit.
Canadian researchers report that such promiscuity lowers the risk of prostate cancer by 28 percent. The same did not hold true if a man had sex with a similar amount of men, however.
In fact, having that many male partners doubled the chances of prostate cancer, the study found. Quantity seemed key: If a man had only one male sexual partner, prostate cancer risk was no greater than if a man never had any male sexual partners, the study found.
Apparently, it is the frequency of ejaculations that may explain the difference between one female partner and many, the study authors said.
"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 in [other] cohort studies," said lead researcher Marie-Elise Parent, of the University of Montreal's School of Public Health.
In this study of more than 3,000 men, those who had more than 20 female partners were also 19 percent less likely to get a more aggressive type of prostate cancer. But having more than 20 male partners upped the chances of a less aggressive prostate cancer five-fold, the researchers found.
They theorize that any benefit to men from having multiple partners may be offset when having sex with men because of the possibility of more exposure to sexually transmitted diseases, and the potential of the prostate being harmed by anal sex.
The researchers also reported that having a relative with prostate cancer doubled the chances of a man getting the disease himself.
The findings were published Oct. 28 in the journal Cancer Epidemiology.
Visit the American Cancer Society for more on prostate cancer.