|New Scientist, 4/6/2004 - Frequent sexual intercourse and masturbation protects men against a common form of cancer, suggests the largest study of the issue to date yet. Journal of the American Medical Association (vol 291, p 1578). |
The US study, which followed nearly 30,000 men over eight years, showed that those that ejaculated most frequently were significantly less likely to get prostate cancer. The results back the findings of a smaller Australian study revealed by New Scientist in July 2003 that asserted that masturbation was good for men.
In the US study, the group with the highest lifetime average of ejaculation - 21 times per month - were a third less likely to develop the cancer than the reference group, who ejaculated four to seven times a month.
Michael Leitzmann, at the National Cancer Institute in Bethesda, Maryland, and colleagues set out to test a long-held theory that suggested the opposite - that a higher ejaculation rate raises the risk of prostate cancer. "The good news is it is not related to an increased risk," he told New Scientist. In fact, it "may be associated with a lower risk."
"It goes a long way to confirm the findings from our recent case-control study," says Graham Giles, who led the Australian study. He praises the study's large size - including about 1500 cases of prostate cancer.
Furthermore, it was the first to begin by following thousands of healthy men. This rules out some of the biases which might be introduced by asking men diagnosed with prostate cancer to recall their sexual behaviour retrospectively.
At the start of the study, the men filled in a history of their ejaculation frequency and then filled in further questionnaires every two years.
Men of different ages varied in how often they ejaculated, so the team used a lifetime average for comparisons. Compared to the reference group who ejaculated four to seven times a month, "each increase of three ejaculations per week was associated with a 15 per cent decrease in the risk of prostate cancer", says Leitzmann.
"More than 12 ejaculations per month would start conferring the benefit - on average every second day or so," he says.
However, whilst the findings are statistically significant, Leitzmann remains cautious. "I don't believe at this point our research would warrant suggesting men should alter their sexual behaviour in order to modify their risk."
A further caveat is that the benefit of ejaculation was less clear in relation to the most dangerous, metastasising form of prostate cancer, compared to the organ-confined or slow-growing types.
Leitzmann and Giles both agree that there are biologically plausible ways that ejaculating frequently might prevent prostate cancer.
"Increased ejaculation may allow the prostate gland to clear itself of carcinogens or of materials that form a substrate for the development of carcinogens," Giles told New Scientist.
Another theory is that frequent drainage of prostate fluid stops tiny crystalloid microcalcifications - which have been associated with prostate cancer - from forming in the prostate duct, says Leitzmann.
Giles notes that neither study examines ejaculation during the teenage years - which may be a crucial factor. But he says: "Although much more research remains to be done, the take home message is that ejaculation is not harmful, and very probably protective of prostatic health - and it feels good!"
Frequent Ejaculation May Be Good for Prostate
WebMD Medical News, 4/6/2004 - In a study published in the The Journal of the American Medical Association, men who ejaculated most often had a 33% lower lifetime risk of prostate cancer.
Men who reported 21 or more ejaculations per month in their 40s had a 32% lower risk of prostate cancer later in life compared with those who reported between four and seven ejaculations per month. Men who reported more than 21 monthly ejaculations in the previous year had a 51% lower risk of prostate cancer.
Overall, an average of 21 or more ejaculations a month during a man's lifetime decreased the risk of prostate cancer later in life by 33%. And each increase of three ejaculations per week during a man's lifetime was associated with a 15% reduction in prostate cancer risk.
Ejaculation may protect the prostate through a variety of biological mechanisms that merit further research, such as:
According to the American Cancer Society, prostate cancer is the most common type of cancer found in American men, other than skin cancer. They estimate that about 230,900 new cases of prostate cancer will be diagnosed this year in the U.S., and close to 30,000 American men will die of this disease.
Australian Study - Masturbating May Protect Against Prostate Cancer
New Scientist, 7/16/2003 - A team in Australia led by Graham Giles of The Cancer Council Victoria in Melbourne asked 1079 men with prostate cancer to fill in a questionnaire detailing their sexual habits, and compared their responses with those of 1259 healthy men of the same age. The team concludes that the more men ejaculate between the ages of 20 and 50, the less likely they are to develop prostate cancer.
The protective effect is greatest while men are in their twenties: those who had ejaculated more than five times per week in their twenties, for instance, were one-third less likely to develop aggressive prostate cancer later in life (BJU International, vol 92, p 211).
The results contradict those of previous studies, which have suggested that having had many sexual partners, or a high frequency of sexual activity, increases the risk of prostate cancer by up to 40 per cent. The key difference is that these earlier studies defined sexual activity as sexual intercourse, whereas the latest study focused on the number of ejaculations, whether or not intercourse was involved.
The team speculates that infections caused by intercourse may increase the risk of prostate cancer. "Had we been able to remove ejaculations associated with sexual intercourse, there should have been an even stronger protective effect of other ejaculations," they suggest. "Men have many ways of using their prostate which do not involve women or other men," Giles adds.
Giles accepts the possibility that the men who completed the questionnaires could have lied about their habits. But he doubts this skewed the results, since questions about masturbation are unlikely to evoke the same macho exaggeration as questions about, say, number of sexual partners.
But why should ejaculating more often cut the risk of prostate cancer? The team speculates that ejaculation prevents carcinogens building up in the gland. The prostate, together with the seminal vesicles, secretes the bulk of the fluid in semen, which is rich in substances such as potassium, zinc, fructose and citric acid.
Generating the fluid involves concentrating these components from the bloodstream up to 600-fold - and this could be where the trouble starts. Studies in dogs show that carcinogens such as 3-methylcholanthrene, found in cigarette smoke, are also concentrated in prostate fluid.
"It's a prostatic stagnation hypothesis," says Giles. "The more you flush the ducts out, the less there is to hang around and damage the cells that line them."
His findings suggest an intriguing parallel between prostate cancer and breast cancer, as recent studies indicate that lactating reduces a woman's risk of breast cancer, perhaps because this also flushes out carcinogens. Alternatively, ejaculation might induce prostate cells to mature fully, making them less susceptible to carcinogens.
"All these mechanisms are totally speculative," cautions breast cancer expert Loren Lipworth of the International Epidemiology Institute in Rockville, Maryland.
But if the finding is confirmed, future health advice from doctors may no longer be restricted to diet and exercise. "Masturbation is part of people's sexual repertoire," says Anthony Smith, deputy director of the Australian Research Centre in Sex, Health and Society at La Trobe University in Melbourne.
"If these findings hold up, then it's perfectly reasonable that men should be encouraged to masturbate," he says.
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