title: Associations of body size and reproductive factors with circulating levels of sex hormones and prolactin in premenopausal Japanese women.
abstract: OBJECTIVE
  Body size and reproductive factors are important risk factors of breast cancer. The aim of the present study was to examine the associations of these factors with blood concentrations of sex hormones and prolactin in premenopausal Japanese women.
  
  
  METHODS
  We measured the plasma concentrations of estradiol, estrone, testosterone, dehydroepiandrosterone sulfate (DHEAS), sex hormone-binding globulin (SHBG), follicle-stimulating hormone, luteinizing hormone, and prolactin among 436 women who had regular menstrual cycles less than 40 days long. Information on menstrual and reproductive factors including history of breastfeeding was obtained using a self-administered questionnaire. Height and weight were measured.
  
  
  RESULTS
  After controlling for age and the phase of the menstrual cycle, the body mass index (BMI) was significantly inversely associated with total estradiol, estrone and SHBG and significantly positively associated with total and free testosterone and DHEAS. Nulliparous women had significantly higher levels of total and free testosterone, DHEAS, and prolactin than parous women. Duration of breastfeeding for the first child was significantly inversely associated with free testosterone and prolactin levels.
  
  
  CONCLUSIONS
  The data suggest that an increased risk of premenopausal breast cancer associated with low BMI is partially mediated by an increased total estradiol. Androgens and prolactin may explain the breast cancer protection provided by giving birth and breastfeeding.
authors.affiliation: Department of Epidemiology & Preventive Medicine, Gifu University Graduate School of Medicine, Gifu, 501-1194, Japan. chisato@gifu-u.ac.jp
authors.forename: Chisato
authors.initials: C
authors.lastname: Nagata
authors.forename: Keiko
authors.initials: K
authors.lastname: Wada
authors.forename: Kozue
authors.initials: K
authors.lastname: Nakamura
authors.forename: Makoto
authors.initials: M
authors.lastname: Hayashi
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Takeda
authors.forename: Keigo
authors.initials: K
authors.lastname: Yasuda
mesh_terms: D000328:Adult; D044466:Asian People / Q000706:statistics & numerical data; D015992:Body Mass Index; D049628:Body Size / Q000502:physiology*; D001942:Breast Feeding / Q000453:epidemiology; D001943:Breast Neoplasms / Q000097:blood / Q000453:epidemiology / Q000208:ethnology / Q000209:etiology; D002277:Carcinoma / Q000097:blood / Q000453:epidemiology / Q000209:etiology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006801:Humans; D008875:Middle Aged; D017697:Premenopause / Q000097:blood* / Q000502:physiology; D011388:Prolactin / Q000097:blood*; D017584:Reproductive History; D012307:Risk Factors
chemical_list: D012739:Gonadal Steroid Hormones; D011388:Prolactin