title: A prospective study of physical activity and risk of prostate cancer in US physicians.
abstract: BACKGROUND
  Exercise can suppress androgen production and may thus decrease the risk of prostate cancer. However, findings from epidemiological studies assessing physical activity and risk of prostate cancer are inconsistent.
  
  
  METHODS
  We prospectively examined the association between physical activity and prostate cancer risk in the Physicians' Health Study (PHS), a randomized trial of low-dose aspirin and beta-carotene among 22,071 men aged 40-84 without self-reported myocardial infarction, stroke and cancer. At baseline in 1982, men were asked about the frequency of exercise vigorous enough to work up a sweat. Physical activity was assessed in a similar fashion again at 36 months of follow-up.
  
  
  RESULTS
  During 11.1 years of follow-up (258 779 person-years), 982 cases of prostate cancer occurred and were confirmed by medical record review. After adjustment for potential confounding factors (including age, height, randomized treatment assignment, smoking status, alcohol intake, use of multivitamins, history of diabetes, history of hypertension and history of high cholesterol), the relative risks for prostate cancer associated with exercise vigorous enough to work up a sweat were 1.0 (referent) for frequency less than once per week, 1.02 (95% CI: 0.82-1.26) for once per week, 1.07 (95% CI: 0.90-1.27) for 2-4 times per week, and 1.11 (95% CI: 0.90-1.36) for 5+ times per week. Across all subgroups of men categorized by age, body mass index, smoking status, alcohol intake, use of multivitamins, history of diabetes, history of hypertension and history of high cholesterol, there were no significant associations between frequency of exercise vigorous enough to work up a sweat and prostate cancer risk. After excluding cases of prostate cancer that occurred during the first 36 months of follow-up, again, there was no significant association. Combining physical activity assessments at baseline and at 36 months also yielded no significant association with prostate cancer risk.
  
  
  CONCLUSIONS
  These observational data from the Physicians' Health Study do not support the hypothesis that increased physical activity reduces the risk of prostate cancer.
authors.affiliation: Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02215, USA.
authors.forename: S
authors.initials: S
authors.lastname: Liu
authors.forename: I M
authors.initials: IM
authors.lastname: Lee
authors.forename: P
authors.initials: P
authors.lastname: Linson
authors.forename: U
authors.initials: U
authors.lastname: Ajani
authors.forename: J E
authors.initials: JE
authors.lastname: Buring
authors.forename: C H
authors.initials: CH
authors.lastname: Hennekens
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015444:Exercise; D006801:Humans; D008297:Male; D008875:Middle Aged; D010820:Physicians / Q000706:statistics & numerical data*; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000453:epidemiology* / Q000517:prevention & control; D012306:Risk; D014481:United States / Q000453:epidemiology