Men who ejaculate frequently may have a lower occurrence of prostate cancer, said a National Cancer Institute official.

A study at Harvard University showed men with higher ejaculation frequencies have a lower probability of developing prostate cancer, contrary to nearly all previous studies, said Michael Leitzmann, researcher at the National Cancer Institute and author of the study in a phone interview.

Frequent ejaculation may release cancer-causing carcinogens in the prostate glands. Carcinogens enter the glands through bloodstream and tissue via diet and environment, Leitzmann said.

“Ejaculation could flush out these chemicals in semen,” he said.

Leitzmann, who worked on the study while a fellow at Harvard, said the reasons for the contrary results are because the study was conducted in a more objective manner.

Previous studies followed a case control study design, Leitzmann said. Men with prostate cancer were asked to fill out a questionnaire on ejaculation frequency after diagnosed with prostate cancer. A control group of men who did not have prostate cancer were asked the same questions, and the results were compared.

“The problem with this type of study is the control group may recall their history more accurately because they have no recall bias,” Leitzmann said.

A recall bias occurs when members of the study do not remember their past history accurately because of a recent diagnoses. For example, men with prostate cancer may recall higher past frequencies of ejaculation in order to explain their disease, when the control group would not.

In this study, men whose tests for prostate cancer came back negative were asked to participate in the study. About 30,000 men were asked to report on past sexual history. These men were then tracked for eight years, and the ejaculation frequency of men who developed prostate cancer were compared with that of those who did not.

Leitzmann does not believe the study has direct public health implications.

“[I] should not recommend changing sexual habits to lower risk of prostate cancer,” he said. “More research is needed before we can make recommendations.”

Leitzmann said he hopes the study will lead to further research in molecular and biological mechanisms through which increased ejaculation frequency may decrease the probability of prostate cancer.

Leo Milleman, urologist at McFarland Clinic, said the study will help answer a question that men talk about amongst each other.

“It’s a reportable quote to answer a question that’s thrown around in casual talk,” he said. “It’s real scientific data to support casual conversations.”

Milleman said he would discuss the study with patients depending on the appropriateness of the situation.

The reasons for decreased risk of prostate cancer are not entirely known, Leitzmann said. Doctors need to refer to other studies in order to find out what is happening biologically.