An Australian study that was reported by the BBC back in 2003 found that cancer-causing chemicals could build up in the prostate if men do not ejaculate regularly.
The study went on to suggest that sexual intercourse may not have the same benefit because of the possibility of contracting a sexually transmitted disease, which could increase chance of getting cancer.
The Australian researchers questioned 1,000 men who had prostate cancer and 1,250 who didn't about their sexual habits. Those who ejaculated the most between 20 and 50 were less likely to develop prostate cancer.
Men who ejaculated more than five times a week were a third less likely to develop prostate cancer later in life.
Graham Giles of the Cancer Council Victoria in Melbourne said ejaculating may prevent carcinogens accumulating in the prostate gland. Fewer ejaculations may cause those carcinogens to build up.
"It's a prostatic stagnation hypothesis. The more you flush the ducts out, the
less there is to hang around and damage the cells that line them."
Here's a link to that BBC story, "Masturbation cuts cancer risk."
In spite of it being five years old, the story got a second wind this week when it was reported in PlanetOut on Monday, attributing it to a BBC story on Wednesday (yeah, Wednesday five years ago). The US News & World Report science blog called them out for drudging up this old news.
Old news or not, it's an interesting theory. Sure it's a ha-ha, wink-wink kind of story, but if valid, it certainly deserves to be pursued.