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.

"We were keen to look at the links between sexual activity and younger men as a lot of prostate cancer studies focus on older men as the disease is more prevalent in men over 50" says lead author Dr. Polyxeni Dimitropoulou, who is now at the University of Cambridge.

"Hormones appear to play a key role in prostate cancer and it is very common to treat men with therapy to reduce the hormones thought to stimulate the cancer cells. A man's sex drive is also regulated by his hormone levels, so this study examined the theory that having a high sex drive affects the risk of prostate cancer."

The study participants, who were recruited by their family doctors, were asked to fill in a questionnaire about their sexual habits in each decade of their life since their twenties.

All the men with prostate cancer had been diagnosed in their fifties. Most of the men who took part in the study (97%) were white and the majority were currently married (84%) or widowed, separated or divorced (12%).

A number of interesting points came out of the study:

• 59% of the men in both groups said that they had engaged in sexual activity (intercourse or masturbation) 12 times a month or more in their twenties. This fell steadily as they got older, to 48% in their thirties, 28% in their forties and 13% in their fifties.

• 39% of the cancer group had had six female partners or more, compared with 31% of the control group.

• Men with prostate cancer were more likely to have had a sexually transmitted disease than those without prostate cancer.

• More men with prostate cancer fell into the highest frequency groups in each decade when it came to sexual activity (intercourse and masturbation) than men in the control group. 40% of men in the cancer group fell into the highest frequency category in their twenties (20 or more times a month) compared to 32% in the control group. Similar patterns were observed in the men's thirties and forties. By the fifties it had evened out, with 31% in each group falling into the most frequent category (ten or more times a month).

• Men with prostate cancer were also more likely to masturbate frequently than men in the control group, with the greatest difference in the twenties (34% versus 24%) and thirties (41% versus 31%). The differences were less pronounced in their forties (34% versus 28%) and by the fifties the cancer group was slightly lower (25% versus 26%).

"What makes our study stand out from previous research is that we focused on a younger age group than normal and included both intercourse and masturbation at various stages in the participants' lives" says Dr. Dimitropoulou.

"Overall we found a significant association between prostate cancer and sexual activity in a man's twenties and between masturbation and prostate cancer in the twenties and thirties. However there was no significant association between sexual activity and prostate cancer in a man's forties.