Contrary to some research, frequent sexual activity does not increase the risk of developing prostate cancer and might even reduce the danger, a study of nearly 30,000 men found.
Some previous studies have suggested that men who have frequent ejaculations - whether through sex or masturbation - might be more prone to prostate cancer. One theory is that lots of sex exposes men to various germs and viruses that somehow lead to prostate cancer.
The latest study should be "reassuring to those men who may be more active than others,'' said Dr. Durado Brooks, prostate cancer director for the American Cancer Society.
The study involved 29,342 health professionals ages 46 to 81 who were asked about their ejaculations in their 20s, 40s and during the previous year, 1991. During about eight years of follow-up, 1,449 men developed prostate cancer.
On average, the men overall had four to seven ejaculations a month. No increased risk of prostate cancer was seen in men who reported more frequent ejaculations, and there appeared to be a decreased risk in men with the highest reported levels.
The two highest activity levels - 13 to 20 ejaculations a month, and at least 21 a month - were linked with decreased cancer risks of 14 percent and 33 percent respectively.
One theory is that frequent ejaculations help flush out cancer-causing chemicals or reduce the development of calcifications that have been linked with prostate cancer.
But relatively few men in the study reported heavy sexual activity, so more research is needed to establish whether there is, in fact, a link, said Dr. Michael Leitzmann, a researcher at the National Cancer Institute who led the study.
"It's too early to suggest that men should change their sexual habits to alter their prostate cancer risk,'' he said.
The study appears in Wednesday's Journal of the American Medical Association.
The theorized connection between frequent sexual activity and prostate cancer is not entirely far-fetched: High levels of the male hormone testosterone can cause a strong sex drive and can also fuel the growth of cancer cells.
The study involved mostly white men. Leitzmann said it is unclear whether similar results would be found in blacks, who have much higher prostate cancer risks than whites. But he said the biological mechanisms that might explain the results probably do not differ by race.
Prostate cancer is the second most common cancer in men, after skin cancer. One in every six men will develop it.
The American Cancer Society estimates that this year, 230,900 new cases will be diagnosed and that about 29,900 men will die from prostate cancer.
The walnut-sized prostate gland produces fluids that are contained in semen.