title: Pregnancy and lactation have no long-term deleterious effect on measures of bone mineral in healthy women: a twin study.
abstract: BACKGROUND
  The long-term effects of pregnancy and lactation on measures of bone mineral in women remain unclear.
  
  
  OBJECTIVE
  We studied whether pregnancy or lactation has deleterious long-term effects on bone mineral in healthy women.
  
  
  METHODS
  We measured bone mineral density (BMD; g/cm(2)) in women aged > or = 18 y. Analyses were performed on 3 data sets: study 1, 83 female twin pairs (21 monozygous and 62 dizygous) aged (x +/- SD) 42.2 +/- 15.5 y who were discordant for ever having been pregnant beyond 20 wk; study 2, 498 twin pairs aged 42.3 +/- 15.0 y; and study 3, 1354 individual twins, their siblings, and family members.
  
  
  RESULTS
  In study 1, there were no significant within-pair differences in unadjusted BMD or BMD adjusted for age, height, and fat mass at the lumbar spine or total-hip or in total-body bone mineral content (BMC; kg) (paired t tests). In study 2, there was no significant within-pair difference in measures of bone mineral or body composition related to the within-pair difference in number of pregnancies. In study 3, subjects with 1 or 2 (n = 455) and > or = 3 pregnancies (n = 473) had higher adjusted lumbar spine BMD (2.9% and 3.8%, respectively; P = 0.001) and total-body BMC (2.2% and 3.1%; P < 0.001) than did nulliparous women (n = 426). Parous women who breast-fed had higher adjusted total-body BMC (2.6%; P = 0.005), total-hip BMD (3.2%; P = 0.04), and lower fat mass (10.9%; P = 0.01) than did parous non-breast-feeders.
  
  
  CONCLUSIONS
  We found no long-term detrimental effect of pregnancy or breast-feeding on bone mineral measures.
authors.affiliation: University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville, Victoria, Australia.
authors.forename: Lynda M
authors.initials: LM
authors.lastname: Paton
authors.forename: Jo L
authors.initials: JL
authors.lastname: Alexander
authors.forename: Caryl A
authors.initials: CA
authors.lastname: Nowson
authors.forename: Claire
authors.initials: C
authors.lastname: Margerison
authors.forename: Mandy G
authors.initials: MG
authors.lastname: Frame
authors.forename: Bahtiyar
authors.initials: B
authors.lastname: Kaymakci
authors.forename: John D
authors.initials: JD
authors.lastname: Wark
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D015519:Bone Density; D002136:Calcium, Dietary / Q000008:administration & dosage; D003430:Cross-Sectional Studies; D005260:Female; D006615:Hip / Q000000981:diagnostic imaging; D006801:Humans; D007774:Lactation / Q000502:physiology*; D008875:Middle Aged; D011247:Pregnancy / Q000502:physiology*; D012189:Retrospective Studies; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D002136:Calcium, Dietary