From PhysOrg:

Men who are very sexually active in their twenties and thirties are more likely to develop prostate cancer, especially if they masturbate frequently, according to a study of more than 800 men published in the January issue of BJU International.

However the UK research team also found that frequent sexual activity in a man’s forties appears to have little effect and even small levels of activity in a man’s fifties could offer protection from the disease. Most of the differences were attributed to masturbation rather than sexual intercourse.

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.

Men who took part in the study were asked about all aspects of their sex life from their twenties onwards, including how old they were when they became sexually active, how often they masturbated and had intercourse, how many sexual partners they had had and whether they had had any sexually transmitted diseases.