- Men who ejaculate often may have a lower risk of prostate cancer than their peers who don't do it as frequently, a U.S. study suggests.

Researchers followed about 32,000 men starting in 1992 when they were in their 20s and continuing through 2010. During this period, almost 4,000 of the men were diagnosed with prostate cancer.

Men who ejaculated at least 21 times a month were 19 percent less likely to be diagnosed with prostate cancer in their 20s than men who ejaculated no more than seven times a month, the study found. By their 40s, men who ejaculated more often were 22 percent less likely to get a prostate cancer diagnosis.

"Ejaculation frequency is, to some extent, a measure of overall health status in that men at the very low end of ejaculation - 0 to 3 times per month - were more likely to have other (medical problems) and die prematurely from causes other than prostate cancer," said lead study author Jennifer Rider, who did the analysis while working at the Harvard T.H. Chan School of Public Health in Boston.

"While our findings should be confirmed in studies that evaluate the potential biological mechanisms underlying the observed associations, the results of our study suggest that ejaculation and safe sexual activity throughout adulthood could be a beneficial strategy for reducing the risk of prostate cancer," Rider, now at Boston University, added by email.

Prostate cancer accounts for 15 percent of all new cancer diagnoses worldwide, the researchers note in the journal European Urology. Established risk factors like age, race and family history are not "modifiable," they add, and there are few lifestyle changes that can be recommended to men to lower risk.

To understand the connection between ejaculation frequency and cancer, Rider and colleagues reviewed data from questionnaires men completed about sexual health and examined medical records and lab tests to verify which participants were diagnosed with prostate tumors.

During the study period, there were 192 cases of prostate cancer among men who ejaculated no more than three times a month. There were 1,041 cases with 4 to 7 ejaculations a month, and 1,509 cases with 8 to 12 monthly ejaculations, another 807 cases with 13 to 20 ejaculations a month and 290 cases with at least 21 monthly ejaculations.

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One limitation of the study is that it relied on men to accurately recall and report how often they ejaculated, the authors note. The study also included mostly white men, and it's possible the results might look different in a more diverse population.

The apparent protective effect of high ejaculation frequency was seen mainly in reduced numbers of low-risk forms of prostate cancer, the authors note.

The association between ejaculation frequency and cancer is also strongest for men without symptoms of prostate tumors such as pain or urinary difficulties that are already at low-risk for these malignancies, said Dr. Behfar Ehdaie, a urology specialist at Memorial Sloan Kettering Cancer Center in New York who wasn't involved in the study.

"If ejaculation frequency was truly a causal factor for prostate cancer development, we would expect to find the association across all prostate cancer risk categories," Ehdaie said by email.

It's also too soon to weigh the merits of sex as a tool for cancer prevention, said Siobhan Sutcliffe, a cancer researcher at Washington University School of Medicine in St. Louis who wasn't involved in the study.

"Sexual activity can have some negative health consequences, such as acquiring a sexually transmitted infection," Sutcliffe noted by email.

Frequent ejaculation through sex or masturbation probably results from other factors that contribute to good health, such as a healthy diet and normal weight, which might also lower the risk of cancer, said Dr. John Gore, a urology researcher at the University of Washington in Seattle who wasn't involved in the study.

"I do not think we need to tell men `if you don't use it, you lose it,'" Gore said by email. "If lower ejaculation frequency prompts a man to schedule a visit with a primary care provider or specialist, and that visit serves to examine and promote preventive care and wellness, then that would be a successful application of the results of this study."