title: Usual physical activity and endogenous sex hormones in postmenopausal women: the European prospective investigation into cancer-norfolk population study.
abstract: BACKGROUND
  Short-term trials indicate that intensive physical activity may influence endogenous sex hormone concentrations. However, the relationship between usual daily physical activity and endogenous hormones in postmenopausal women in the general population is still uncertain.
  
  
  OBJECTIVE
  To determine the relationship between usual physical activity and endogenous sex hormones in postmenopausal women. A cross-sectional population-based study of 2,082 postmenopausal women ages 55 to 81 years, residing in the general community of Norfolk, United Kingdom, and not currently using hormone replacement therapy were chosen to participate. Physical activity in the past 1 year was assessed using a validated questionnaire, and endogenous sex hormone and sex hormone-binding globulin (SHBG) concentrations were determined.
  
  
  RESULTS
  Usual physical activity levels were inversely associated with circulating concentrations of testosterone and estradiol, testosterone/SHBG ratio, and positively associated with SHBG. These associations were only slightly attenuated after adjusting for potential covariates including body mass index, smoking status, alcohol intake, and reproductive variables. Testosterone concentrations and testosterone/SHBG ratios were 19% [95% confidence interval (95% CI), 9-27%, P < 0.001] and 24.0% (95% CI, 13-34% P < 0.001) lower, respectively, whereas estradiol concentrations were 6% (95% CI, 0-12%; P < 0.05) lower in the highest compared with lowest activity levels, respectively. A decreasing trend for the estradiol/SHBG ratio and 17alpha-hydroxyprogesterone concentrations was also observed. Androstenedione levels did not differ significantly according to physical activity.
  
  
  CONCLUSIONS
  Higher usual physical activity levels among postmenopausal women seem to be related to lower endogenous testosterone and estradiol concentrations. This may be one mechanism that could partly explain the reported inverse relationship between physical activity and breast cancer risk in some studies.
authors.affiliation: Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge School of Clinical Medicine, Cambridge, United Kingdom.
authors.forename: Mei-Fen
authors.initials: MF
authors.lastname: Chan
authors.forename: Mitch
authors.initials: M
authors.lastname: Dowsett
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Folkerd
authors.forename: Sheila
authors.initials: S
authors.lastname: Bingham
authors.forename: Nicholas
authors.initials: N
authors.lastname: Wareham
authors.forename: Robert
authors.initials: R
authors.lastname: Luben
authors.forename: Ailsa
authors.initials: A
authors.lastname: Welch
authors.forename: Kay-Tee
authors.initials: KT
authors.lastname: Khaw
mesh_terms: D019326:17-alpha-Hydroxyprogesterone / Q000097:blood; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D000735:Androstenedione / Q000097:blood; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004958:Estradiol / Q000097:blood* / Q000378:metabolism; D004970:Estrone / Q000097:blood; D005260:Female; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D017698:Postmenopause / Q000097:blood / Q000502:physiology*; D011446:Prospective Studies; D012738:Sex Hormone-Binding Globulin / Q000032:analysis; D011795:Surveys and Questionnaires; D013739:Testosterone / Q000097:blood* / Q000378:metabolism; D006113:United Kingdom
chemical_list: D012738:Sex Hormone-Binding Globulin; D004970:Estrone; D013739:Testosterone; D000735:Androstenedione; D004958:Estradiol; D019326:17-alpha-Hydroxyprogesterone