title: Calcium absorption is significantly higher in adolescents during pregnancy than in the early postpartum period.
abstract: BACKGROUND
  Early childbearing may limit skeletal consolidation and increase calcium demands in adolescents.
  
  
  OBJECTIVE
  The purpose of this study was to characterize calcium absorption in pregnant and lactating adolescents.
  
  
  METHODS
  Fractional calcium absorption was evaluated in 23 adolescents (mean +/- SD age: 16.5 +/- 1.4 y) during the third trimester of pregnancy (34.7 +/- 1.0 wk gestation) and again in 15 of these adolescents 31 +/- 8 d after delivery. Eight adolescents were breastfeeding their infants during the follow-up study. Fractional calcium absorption was determined by using oral ((46)Ca or (44)Ca) and intravenous ((42)Ca) stable calcium isotopes. Total-body and lumbar spine bone mineral density were measured in adolescents during the postpartum period by using dual-energy X-ray absorptiometry.
  
  
  RESULTS
  Fractional calcium absorption was significantly greater during pregnancy than at 3-4 wk postpartum [0.526 +/- 0.152 (n = 23) compared with 0.297 +/- 0.108 (n = 15); P < 0.0001]. Lumbar spine z scores measured 19-44 d after delivery (n = 15) were significantly associated with calcium intake during pregnancy (y = -3.53 + 0.107x; R(2) = 0.355, P < 0.02) and were inversely related to fractional calcium absorption during pregnancy (y = 3.489 - 6.66x; R(2) = 0.52, P = 0.002). A total of 33% (5/15) of adolescents had lumbar spine z scores that met the definition of osteopenia (n = 3) or osteoporosis (n = 2) in the early postpartum period.
  
  
  CONCLUSIONS
  Calcium absorption in adolescents was significantly higher during the third trimester of pregnancy than in the early postpartum period, and higher calcium intakes during pregnancy appeared to be protective against loss of trabecular bone at the lumbar spine.
authors.affiliation: Center for Human Nutrition, The Johns Hopkins University Bloomberg School of Public Health, 615 North Wolfe Street, Room 2041, Baltimore, MD 21205-2179, USA. kobrien@jhsph.edu
authors.forename: Kimberly O
authors.initials: KO
authors.lastname: O'Brien
authors.forename: Maureen Schulman
authors.initials: MS
authors.lastname: Nathanson
authors.forename: Jeri
authors.initials: J
authors.lastname: Mancini
authors.forename: Frank R
authors.initials: FR
authors.lastname: Witter
mesh_terms: D015502:Absorptiometry, Photon; D000222:Adaptation, Physiological; D000293:Adolescent; D015519:Bone Density / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics*; D002127:Calcium Isotopes; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D007774:Lactation / Q000378:metabolism*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000378:metabolism; D049590:Postpartum Period / Q000378:metabolism*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000378:metabolism; D011253:Pregnancy in Adolescence / Q000378:metabolism*
chemical_list: D002127:Calcium Isotopes; D002118:Calcium