title: Prospective study of recreational physical activity and ovarian cancer.
abstract: BACKGROUND
  It has been hypothesized that physical activity may reduce the risk of ovarian cancer by decreasing estrogen levels, reducing body fat, and reducing the frequency of ovulation. Epidemiologic studies of this relationship have obtained inconsistent results. The only prospective study to date reported a positive association between frequent vigorous exercise and ovarian cancer risk. We further evaluated this relationship in the Nurses' Health Study cohort.
  
  
  METHODS
  Participation in recreational physical activity was assessed by questionnaire in 1980, 1982, 1986, 1988, 1992, and 1994, with questions assessing exercise frequency, duration, and intensity. Results were adjusted for age, parity, oral contraceptive use, tubal ligation, and other risk factors for ovarian cancer. All statistical tests were two-sided.
  
  
  RESULTS
  During a 16-year follow-up (from 1980 to 1996), 1.2 million person-years were accrued by 92 825 cohort members, and 377 cases of epithelial ovarian cancer were confirmed. The relative risk (RR) of ovarian cancer for women engaging in recreational physical activity for 7 hours or more per week compared with those reporting less than 1 hour per week was 0.80 (95% confidence interval [CI] = 0.49 to 1.32; P(trend) =.59). When both the frequency and intensity of activity were taken into account, activity level was also not associated with a reduced risk of ovarian cancer. Compared with inactive women, participants reporting high activity in terms of metabolic equivalent task hours (MET hours) were at greater risk of ovarian cancer (RR for 20 to <30 MET hours/week = 1.84 [95% CI = 1.12 to 3.02]; RR for >30 MET hours/week = 1.27 [95% CI = 0.75 to 2.14]).
  
  
  CONCLUSIONS
  Overall, results did not suggest an inverse association between recreational physical activity and ovarian cancer. The possibility of a modest increase in risk with frequent vigorous activity requires further investigation.
authors: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, and Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA. ebertone@schoolph.umass.edu
authors: E R
authors: ER
authors: Bertone
authors: W C
authors: WC
authors: Willett
authors: B A
authors: BA
authors: Rosner
authors: D J
authors: DJ
authors: Hunter
authors: C S
authors: CS
authors: Fuchs
authors: F E
authors: FE
authors: Speizer
authors: G A
authors: GA
authors: Colditz
authors: S E
authors: SE
authors: Hankinson
mesh_terms: D000328:Adult; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009726:Nurses; D010051:Ovarian Neoplasms / Q000453:epidemiology*; D011446:Prospective Studies; D011998:Recreation; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013997:Time Factors; D014481:United States