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While the origins and causes of prostate cancer, among the most common cancers in men, continue to mystify researchers, some scientists naturally enough have begun to investigate possible connections to sexually transmitted infections. One such study from the University of Montreal and the Institut Armand-Frappier uncovered evidence your wife may not be happy to learn. The researchers found no link between STDs and prostate cancer; however, men who have bedded more than 20 lifetime sexual partners showed a decreased risk of prostate cancer, Medical Daily reports.

To understand whether there might be connections between STDs, the number and gender of sexual partners, and prostate cancer risk, a team of researchers collected and analyzed data from the Prostate Cancer & Environment Study or PROtEuS, an investigation of mainly French-speaking men in Montreal. The study included 1,590 cases of prostate cancer diagnosed in a particular Canadian hospital between 2005 and 2009, and 1,618 age-matched “control” subjects without cancer chosen from the Montreal population. Next, the researchers conducted in-person interviews to better understand the demographic, class, lifestyle, and environmental factors in each man’s life.

“We were fortunate to have participants from Montreal who were comfortable talking about their sexuality, no matter what sexual experiences they have had, and this openness would probably not have been the same 20 or 30 years ago," commented Dr. Marie-Elise Parent, a professor at the School of Public Health, in a university press release.

Following the interviews, the team set to work analyzing the data and crunching the numbers. What did they learn?

Men with more than 20 sexual partners (throughout their lives) had a decreased risk of prostate cancer, same as those who specifically had more than 20 female sexual partners. By comparison, having had male sexual partners did not offer the same protection against cancer. In fact, having male partners seemed to increase the risk of a man developing prostate cancer. The researchers speculate trauma to the prostate may occur during same sex intercourse.