title: Cross-sectional study of the effects of parturition and lactation on bone mineral density later in life.
abstract: OBJECTIVE
  The present cross-sectional study investigated the effects of parturition and lactation on bone mineral density (BMD) later in life.
  
  
  METHODS
  The subjects were 456 premenopausal and 713 postmenopausal Japanese women aged 40-69 years old. They were classified into six subgroups at 5-year increments. Age, height, weight, menopausal status, age at menopause (in postmenopausal women), years since menopause (in postmenopausal women), parity, and total lactation period were recorded. Lumbar spine BMD (L2-4) was measured by dual-energy X-ray absorptiometry (DEXA). In each subgroup, correlations of parturition and lactation with BMD were investigated using Pearson's correlation test and multiple regression analyses.
  
  
  RESULTS
  In premenopausal women aged 40-44 years old (n=143), total lactation period was inversely correlated with BMD (r= -0.293, P<0.01). This relationship remained significant after adjusting for age, height, weight, and parity (P<0.05). Although the total lactation period was inversely correlated with BMD in the group aged 60-64 years old (r= -0.194, P<0.05, n=218), this relationship disappeared after adjusting for age, YSM, height, weight, and parity. However, in the other subgroups, there were no significant correlations between total lactation period and BMD. There were no significant correlations observed between parity and BMD in any groups.
  
  
  CONCLUSIONS
  Reproductive history of lactation and parity does not seem to be a major determinant of BMD later in life.
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, Japan.
authors.forename: Nobuko
authors.initials: N
authors.lastname: Kojima
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Douchi
authors.forename: Shouichiro
authors.initials: S
authors.lastname: Kosha
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Nagata
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000368:Aged; D015519:Bone Density; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D007774:Lactation; D008159:Lumbar Vertebrae; D008593:Menopause; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012044:Regression Analysis