This is from the
BBC
"Australian researchers questioned over 1,000 men who had developed prostate cancer and 1,250 who had not about their sexual habits.
They found those who had ejaculated the most between the ages of 20 and 50 were the least likely to develop the cancer.
The protective effect was greatest while the men were in their 20s.
Men who ejaculated more than five times a week were a third less likely to develop prostate cancer later in life."