Editor's Note: This story was revised Jan. 28, 2008 after an email interview with the study's lead author Polyxeni Dimitropoulou to address concerns that this research produced markedly different results than some previous studies on the topic.

A new study finds men who are sexually active in their 20s and 30s are more likely to develop prostate cancer — especially if they masturbate frequently.

The message, perhaps: Hold off until middle age.

The study also found that frequent sexual activity in a man's 40s appears to have little effect and even small levels of sexual activity in a man's 50s could offer protection from the disease. Most of the differences were attributed to masturbation rather than sexual intercourse.

However, some previous studies had generated much different findings. The bottom line: More study is needed to settle this one.

The study, led by the University of Nottingham, looked at the sexual practices of more than 431 men who had been diagnosed with prostate cancer before the age of 60, together with 409 controls who do not have prostate cancer.

Among men with prostate cancer, 34 percent had masturbated frequently in their 20s, compared to 24 percent among the control group. A similar spread was found for men in their 30s.

The results, based on questionnaires, are detailed in the journal BJU International (the British Journal of Urology).

The prostate gland secretes a milky fluid that mixes with sperm and seminal vesicle fluid to become semen. Prostate cancer is the second leading cause of cancer deaths among men in the United States, after lung cancer, according to the Centers for Disease Control and Prevention. About 30,000 die from it each year.

In 2004 (the most recent year for which data are available), 189,075 new cases of prostate cancer were diagnosed in the United States, and 29,002 men died of the cancer.

"We were keen to look at the links between sexual activity and younger men as a lot of prostate cancer studies focus on older men as the disease is more prevalent in men over 50," said lead author Polyxeni Dimitropoulou, who is now at the University of Cambridge.

"Hormones appear to play a key role in prostate cancer and it is very common to treat men with therapy to reduce the hormones thought to stimulate the cancer cells," Dimitropoulou said. "A man's sex drive is also regulated by his hormone levels, so this study examined the theory that having a high sex drive affects the risk of prostate cancer."

Dimitropoulou said more needs to be learned about what's going on in the body before the results should be seen as conclusive, however.

"There are earlier studies which confirm part of our findings or are inconclusive, besides the ones which disagree with our findings," Dimitropoulou told LiveScience. "Until the mechanisms are elucidated and are clearly established we cannot be certain about the outcome of any study."

Other findings:

• 59 percent of the men in both groups said that they had engaged in sexual activity (intercourse or masturbation) 12 times a month or more in their 20s. This fell steadily as they got older, to 48 percent in their 30s, 28 percent in their forties and 13 percent in their 50s.
• 39 percent of the cancer group had had six female partners or more, compared with 31 percent of the control group.
• Men with prostate cancer were more likely to have had a sexually transmitted disease than those without prostate cancer.

"A possible explanation for the protective effect that men in their fifties appear to receive from overall sexual activity, and particularly masturbation, is that the release of accumulated toxins during sexual activity reduces the risk of developing cancer in the prostate area," Dimitropoulou said. "This theory has, however, not been firmly established and further research is necessary."