title: Sexual factors and prostate cancer.
abstract: OBJECTIVE
  To assess whether prostate cancer might be related to hormone levels and, by inference, to differences in sexual activity.
  
  
  METHODS
  In a case-control study of men with prostate cancer aged < 70 years at diagnosis and age-matched control subjects, information was collected on two aspects of sexual activity; the number of sexual partners and the frequency of total ejaculations during the third to fifth decades of life.
  
  
  RESULTS
  There was no association of prostate cancer with the number of sexual partners or with the maximum number of ejaculations in 24 h. There was a negative trend (P < 0.01) for the association between risk and number of ejaculations in the third decade, independent of those in the fourth or fifth. Men who averaged five or more ejaculations weekly in their 20s had an odds ratio (95% confidence interval) of 0.66 (0.49-0.87) compared with those who ejaculated less often.
  
  
  CONCLUSIONS
  The null association with the number of sexual partners argues against infection as a cause of prostate cancer in this population. Ejaculatory frequency, especially in early adult life, is negatively associated with the risk of prostate cancer, and thus the molecular biological consequences of suppressed or diminished ejaculation are worthy of further research.
authors.affiliation: Cancer Epidemiology Centre, and Centre for Behavioural Research in Cancer, The Cancer Council Victoria, Melbourne, Australia. Graham.Giles@cancervic.org.au
authors.forename: G G
authors.initials: GG
authors.lastname: Giles
authors.forename: G
authors.initials: G
authors.lastname: Severi
authors.forename: D R
authors.initials: DR
authors.lastname: English
authors.forename: M R E
authors.initials: MR
authors.lastname: McCredie
authors.forename: R
authors.initials: R
authors.lastname: Borland
authors.forename: P
authors.initials: P
authors.lastname: Boyle
authors.forename: J L
authors.initials: JL
authors.lastname: Hopper
mesh_terms: D000328:Adult; D000368:Aged; D004542:Ejaculation; D004812:Epidemiologic Methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000503:physiopathology / Q000523:psychology*; D012725:Sexual Behavior; D012747:Sexual Partners