title: Lifetime cumulative number of menstrual cycles and serum sex hormone levels in postmenopausal women.
abstract: OBJECTIVE
  Lifetime cumulative number of menstrual cycles is related to breast cancer risk. The aim of this study is to investigate the relation between this index and serum sex hormone levels in postmenopausal women.
  
  
  METHODS
  Cross-sectional study including 860 naturally postmenopausal Dutch participants of the European Prospective Investigation into Cancer and Nutrition. Lifetime cumulative number of menstrual cycles was computed using questionnaire data on ages at menarche and menopause, number of pregnancies, breastfeeding, oral contraceptive use (OC) and regularity pattern. Measurements of hormones included estrone (E1), estradiol (E2), andostrenedione, testosterone, sex-hormone binding globulin (SHBG) and dehydroepiandrostenedione sulfate (DHEAS). The relation between the lifetime cumulative number of menstrual cycles and hormone levels was assessed using analysis of covariance. Relations between reproductive characteristics and hormone levels were also studied. Adjustments for characteristics at blood collection included age, years since menopause, BMI, hormone replacement therapy use, OC use, smoking habits, alcohol intake and physical activity were done.
  
  
  RESULTS
  Lifetime cumulative number of cycles was related with SHBG; participants in the lowest category had higher SHBG levels. For the separate characteristics, DHEAS and androstenedione increased significantly with increasing age at menarche, while androstenedione and testosterone decreased with increasing age at menopause. For the parity characteristics, SHBG levels increased according to the number of live births.
  
  
  CONCLUSIONS
  Lifetime cumulative number menstrual cycles was related only to SHBG. Therefore, free levels of estrogens or androgens may be related to this number of menstrual cycles estimate, reflecting lifetime exposure to ovarian hormones.
authors.affiliation: Julius Center for Health Sciences and Primary care, University Medical Center, Utrecht, The Netherlands. mchavezm@im.wustl.edu
authors.forename: Mariana
authors.initials: M
authors.lastname: Chavez-MacGregor
authors.forename: Carla H
authors.initials: CH
authors.lastname: van Gils
authors.forename: Yvonne T
authors.initials: YT
authors.lastname: van der Schouw
authors.forename: Evelyn
authors.initials: E
authors.lastname: Monninkhof
authors.forename: Paulus A H
authors.initials: PA
authors.lastname: van Noord
authors.forename: Petra H M
authors.initials: PH
authors.lastname: Peeters
mesh_terms: D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000097:blood* / Q000209:etiology*; D003430:Cross-Sectional Studies; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D008572:Menarche; D008593:Menopause; D008597:Menstrual Cycle; D008875:Middle Aged; D010298:Parity; D017698:Postmenopause; D011247:Pregnancy; D012307:Risk Factors; D012738:Sex Hormone-Binding Globulin / Q000032:analysis
chemical_list: D012739:Gonadal Steroid Hormones; D012738:Sex Hormone-Binding Globulin