"Ejaculation Frequency and Subsequent Risk of Prostate Cancer"
http://jama.ama-assn.org/cgi/content/full/291/13/1578?maxtoshow&RESULTFORMAT=&fu\
lltext=prostate+cancer&searchid=1

Sexual activity has been hypothesized to play a role in the
development of prostate cancer, but epidemiological data are
virtually limited to case-control studies, which may be prone to bias
because recall among individuals with prostate cancer could be
distorted as a consequence of prostate malignancy or ongoing therapy.

The Objective of this research was to examine the association between
ejaculation frequency, which includes sexual intercourse, nocturnal
emission, and masturbation and risk of prostate cancer.

Design, Setting, and Participants:
A prospective study of 29 342 US men aged 46 to 81 years, who
provided information on history of ejaculation frequency on a self-
administered questionnaire. Ejaculation frequency was assessed by
asking participants to report the average number of ejaculations they
had per month during the ages of 20 to 29 years, 40 to 49 years, and
during the past year (1991).

RESULTS
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During 222 426 person-years of follow-up there were 1449 cases of
total prostate cancer, 953 cases of organ-confined prostate cancer,
and 147 cases of advanced prostate cancer. The mean ejaculations per
month at ages 20 to 29 years were 15.1; 40 to 49 years, 11.3; 50 to
59 years, 9.4; and 60 years or older, 5.0.

Fifty-eight percent of men reported an ejaculation frequency of more
than 3 times per week at ages 20 to 29 years, whereas the proportion
of men having more than 3 ejaculations per week decreased to 32% at
ages 40 to 49 years, and further declined to 22% at ages 50 to 59
years and to 5% at ages 60 years or older.

Ejaculation frequency at ages 20 to 29 years showed positive
correlations with ejaculation frequency at ages 40 to 49 years (r =
0.70); 50 to 59 years (r = 0.54); and 60 years or older (r = 0.39);
all P<.001. The number of ejaculations at ages 40 to 49 years was
positively correlated with those at ages 50 to 59 years (r = 0.81)
and 60 years or older (r = 0.53); all P<.001.

Age-standardized lifetime ejaculation frequency was evaluated in
relation to various risk factors for prostate cancer to assess the
potential for confounding (Table 1). Men with greater lifetime
ejaculation frequency tended to be physically more active and were
more likely to have a history of syphilis or gonorrhea, prostatitis,
and vasectomy than men with lower ejaculation frequency.

THE LIFESTYLES OF HIGHLY-SEXED MEN
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In addition, men with greater ejaculation frequency were more likely
to be currently divorced or separated and consumed more total energy,
lycopene, fish, alcohol, supplemental vitamin E, and supplemental
zinc.

Men in the highest category of average lifetime ejaculation frequency
were less likely to have a family history of prostate cancer and a
history of surgery for enlarged prostate than men in the lower
categories of ejaculation frequency. Men in the highest and lowest
categories had a lower prevalence of prostate-specific antigen (PSA)
screening relative to men in the intermediate categories of
ejaculation frequency.