title: Effects of age at first pregnancy and breast-feeding on the development of postmenopausal osteoporosis.
abstract: OBJECTIVE
  Although pregnancy and breast-feeding require adequate calcium mobilization, it is not known if these affect the acquisition of a healthy peak bone mass (PBM) and, hence, postmenopausal osteoporosis (OPS). The objective of this study was to analyze previous pregnancies and/or breast-feeding and their association with OPS.
  
  
  METHODS
  After obtaining institutional review board approval, postmenopausal women (>49 y) presenting for a dual-energy x-ray absorptiometry bone density scan were invited to participate. Risk factors for OPS, including previous fractures, pregnancy information, and dual-energy x-ray absorptiometry results, were collected. OPS was defined as a T score of -2.5 or lower.
  
  
  RESULTS
  Data were obtained from 619 women. Of these, 49.8% were smokers, 27.2% used a bisphosphonate, 64.1% used hormone therapy, and 5.5% had used steroids. Based on PBM, ages at first pregnancy were dichotomized to younger than 27 years and 27 years or older. Women with a history of breast-feeding had a lower prevalence of OPS (7.6%) versus women who had never breast-fed (18.7%; P < 0.001). Women with a first pregnancy when they were 27 years or older and a history of breast-feeding had the lowest prevalence of OPS (4.6%) versus women with a first pregnancy when they were younger than 27 years and no history of breast-feeding (16.3%; P = 0.001).
  
  
  CONCLUSIONS
  Breast-feeding seems to significantly decrease the incidence of postmenopausal OPS. Women whose first pregnancy occurs after PBM (≥27 y of age) and who have a history of breast-feeding had the lowest prevalence of OPS. Thus, an association between OPS and both breast-feeding and age of pregnancy seems to be present.
authors.affiliation: Department of Obstetrics and Gynecology, The Reading Hospital and Medical Center, Reading, PA 19612-6052, USA. schnatzp@readinghospital.org
authors.forename: Peter F
authors.initials: PF
authors.lastname: Schnatz
authors.forename: Kathaleen G
authors.initials: KG
authors.lastname: Barker
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Marakovits
authors.forename: David M
authors.initials: DM
authors.lastname: O'Sullivan
mesh_terms: D015502:Absorptiometry, Photon; D000367:Age Factors; D000368:Aged; D001942:Breast Feeding; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008423:Maternal Age; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000000981:diagnostic imaging / Q000453:epidemiology*; D017698:Postmenopause; D011247:Pregnancy; D015995:Prevalence; D017584:Reproductive History; D012307:Risk Factors