Jan. 27, 2009 -- Frequent masturbation in young men is linked to higher risk of early prostate cancer, but it lowers prostate cancer risk for men in their 50s, a study shows.

High levels of male sex hormones, or androgens, may increase a man's risk of prostate cancer. But different studies of this question, done in different ways, have reached different conclusions.

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.