3,208 men were part of the Prostate Cancer & Environment Study (PROtEuS) in Montreal, Canada. Of these, 1,590 were diagnosed with prostate cancer between 2005 and 2009, while the remaining 1,618 men were free of the disease.
As part of this study, all men were required to complete a questionnaire that asked about their sexual activity, as well as sociodemographic, environmental and lifestyle factors.
Men who had slept with more than 20 women in their lives had a 28% lower risk of developing all types of prostate cancer and a 19% lower risk of developing aggressive prostate cancer, compared with those who had slept with fewer than 20 women.