NEWS YOU CAN USE: Sex with 21 women lowers risk of prostate cancer, academics find; The University of Montreal has found that men who had sex with more than 20 women lower their prostate cancer risk. “Men who had slept with more than 20 women lowered their risk of developing cancer by almost one third, and were 19 per cent less likely to develop the most aggressive form. In contrast, men who slept with 20 men doubled their risk of developing prostate cancer compared with men who have never had sex with another man.”