Scientists say that a key to good prostate health may be ejaculating 21 times a month. According to a study from the Boston University of Public Health which looked at how ejaculation frequency affected prostate cancer risk over the course of 18 years, men ages 20 to 29 who ejaculated 21 times or more each month were 19 percent less likely to be diagnosed with prostate cancer than those who ejaculated less often. It doesn’t just work for young men. Men 40 to 49 who ejaculated 21 times per month reduced their risk of developing prostate cancer by 22 percent. It didn’t matter if the ejaculation was a result of having intercourse or masturbating.