To look at the question in a new way, a team of researchers at England's University of Nottingham looked at whether men with more intense sex drives were at higher risk of prostate cancer.
Polyxeni Dimitropoulou, PhD; Rosalind Eeles, PhD, FRCP; and Kenneth R. Muir, PhD, obtained detailed sexual histories from 840 men. About half the men got prostate cancer by age 60, and about half did not have cancer.
The findings were surprising. Sexual intercourse did not affect prostate cancer risk. But frequent masturbation did -- in different ways, at different times of life.
"Frequent masturbation during men's 20s and 30s increased their risk of prostate cancer," Dimitropoulou tells WebMD. "But men in their 50s who masturbated frequently had decreased risk."
Of course, masturbation frequency is relative.
For men in their 20s, "frequent masturbation" was two to seven times per week. Compared to same-age men who reported masturbating less than once per month, 20-something frequent masturbators had a 79% higher risk of prostate cancer by age 60.
For men in their 50s, "frequent masturbation" was one or more times per week. Compared to same-age men who reported never masturbating, 50-something frequent masturbators had a 70% lower risk of prostate cancer.
What's going on? The study wasn't designed to answer that question. But Dimitropoulou and colleagues have some theories.
They suggest that young men genetically predisposed to have hormone-sensitive prostate cancer will be at higher risk if their bodies naturally produce high levels of male hormones -- the same hormones that give them an intense sex drive.
So it's not masturbation itself that's increasing prostate cancer risk in young men. More masturbation may just mean more sex drive -- and more androgens bathing prostate tissues.
That's not the case for older men. Dimitropoulou suggests that in older men, masturbation itself may actually be helpful, ridding the prostate gland of fluids that may contain cancer-causing substances.
"In mature age, it may be more important that toxins get flushed out of the system," she says. "And because the masturbation frequency was not as high in the men's 50s as it was in their 20s, even low levels of masturbation in the 50s has a protective effect."
These are just theories, Dimitropoulou warns. More research is needed to determine the exact role of sex hormones and sexual activity in prostate-cancer risk at different stages of life.
Meanwhile, Dimitropoulou, now at England's University of Cambridge, advises moderation for both younger and older men.
"It is kind of logical that a moderate level of masturbatory activity has to be maintained," she says. "Not too much, and not none at all."
Dimitropoulou and colleagues report their findings in the January issue of BJU International.