TUESDAY, April 6 (HealthDayNews) -- Sexually active men are not at a greater risk of developing prostate cancer, a new study says, and frequent ejaculation may reduce their chances of getting the disease.

Previous studies have produced conflicting evidence on the risks or benefits of ejaculation in connection with the development of prostate cancer. Some found that increased sexual activity lowers the risk of the tumors, the second most common form of cancer in American men. Others found just the opposite.

The new study, appearing in the April 7 issue of the Journal of the American Medical Association, followed almost 30,000 doctors, dentists, and other health professionals participating in a long-term look at cancer and chronic disease. The men ranged in age from 46 to 81.

As part of the research project, the men, who were mostly white, were asked about their sex life, specifically how frequently they ejaculated -- a question meant to capture not only intercourse but masturbation and nocturnal emissions -- during their 20s, their 40s and in the previous year.

"Not only did [frequent ejaculation] not pose an adverse risk factor, but it possibly could be associated with a lower risk of prostate cancer," said Dr. Michael Leitzmann, an epidemiologist at the National Cancer Institute and the leader of the study.

Men who reported between four and seven ejaculations a month over their adult lifetime had an 11 percent lower chance of developing prostate cancer than those who ejaculated no more than three times a month. Every three-ejaculations-per-week increase across a man's lifetime was associated with a 15 percent drop in prostate cancer risk.

The modest effect of occasional ejaculation could simply illustrate that it doesn't raise the risk of prostate cancer, Leitzmann and his colleagues said.

But men who ejaculated at least 21 times a month had a 33 percent lower chance of developing prostate cancer, suggesting that frequent ejaculation does indeed protect the prostate from growing tumors.

However, the number of cancer cases in this small group was itself small -- only 60 out of the 1,449 cases overall, undercutting the strength of the finding.

Men who reported such frequent ejaculation in the year before entering the study got even more protection against cancer. Again, however, the number of tumor cases in this group was tiny.

How frequent ejaculation might protect the prostate, a walnut-sized gland that provides the liquid medium for sperm during emission, isn't known. The researchers suggest that ejaculation could help purge the prostate of cancer-causing chemicals or stunt the formation of crystalloids that have been linked to tumors in some men.

Another, more speculative, possibility is that the relief of stress associated with ejaculation could lead to hormonal activity that's less likely to promote cancerous changes in the gland.

Until scientists learn more about how the prostate benefits from frequent ejaculation, Leitzmann said, it's too early to recommend that men step up their sexual activity.

"Our study should stimulate progress toward [understanding the mechanism] as opposed to putting out a public health recommendation," he said.

Dr. Graham Giles, an Australian cancer researcher who has looked at sexual activity and prostate cancer risk, said the latest study "goes a long way to confirm" his own group's findings that frequency of ejaculation and prostate tumors are inversely connected.