title: Effect of calcium supplementation on bone resorption in pregnancy and the early postpartum: a randomized controlled trial in Mexican women.
abstract: BACKGROUND
  Calcium needs are physiologically upregulated during pregnancy and lactation to meet demands of the developing fetus and breastfeeding infant. Maternal calcium homeostasis is maintained by hormonal adaptive mechanisms, thus, the role of dietary calcium supplementation in altering maternal responses to fetal-infant demand for calcium is thought to be limited. However, increased calcium absorption is directly related to maternal calcium intake and dietary supplementation has been suggested to prevent transient bone loss associated with childbearing.
  
  
  METHODS
  In a double-blind, randomized placebo-controlled trial, we randomly assigned 670 women in their first trimester of pregnancy to 1,200 mg/day calcium (N = 334) or placebo (N = 336). Subjects were followed through 1-month postpartum and the effect on urinary cross-linked N-telopeptides (NTx) of type I collagen, a specific marker of bone resorption, was evaluated using an intent-to-treat analysis. Women with a baseline and at least one follow-up measurement (N = 563; 84%) were included. Subsequent analyses were conducted stratifying subjects by compliance assessed using pill counts. In random subsets of participants, bone-specific alkaline phosphatase (BAP) (N = 100) and quantitative ultrasound (QUS) (N = 290) were also measured.
  
  
  RESULTS
  Calcium was associated with an overall reduction of 15.8% in urinary NTx relative to placebo (p < 0.001). Among those who consumed ≥50%, ≥67%, and ≥75% of pills, respectively, the effect was associated with 17.3%, 21.3%, and 22.1% reductions in bone resorption (all p < 0.001). There was no significant effect of calcium on bone formation measured by BAP. However, by 1-month postpartum, those in the calcium group had significantly lower NTx/BAP ratios than those in the placebo group (p = 0.04) indicating a net reduction in bone loss in the supplement group by the end of follow-up. Among subjects who consumed ≥50% and ≥75% of pills, respectively, calcium was also associated with an increase of 26.3 m/s (p = 0.03) and 59.0 m/s (p = 0.009) in radial SOS relative to placebo by 1-month postpartum.
  
  
  CONCLUSIONS
  Calcium administered during pregnancy and the early postpartum period, to women with intakes around adequacy, was associated with reduced bone resorption and, thus, may constitute a practical intervention to prevent transient skeletal loss associated with childbearing.
  
  
  BACKGROUND
  ClinicalTrials.gov Identifier NCT00558623.
authors.affiliation: Center for Perinatal, Pediatric, and Environmental Epidemiology, Yale Schools of Public Health and Medicine, 1 Church Street 6th floor, New Haven, CT 06510, USA. adrienne.ettinger@yale.edu.
authors.forename: Adrienne S
authors.initials: AS
authors.lastname: Ettinger
authors.forename: Héctor
authors.initials: H
authors.lastname: Lamadrid-Figueroa
authors.forename: Adriana
authors.initials: A
authors.lastname: Mercado-García
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kordas
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Wood
authors.forename: Karen E
authors.initials: KE
authors.lastname: Peterson
authors.forename: Howard
authors.initials: H
authors.lastname: Hu
authors.forename: Mauricio
authors.initials: M
authors.lastname: Hernández-Avila
authors.forename: Martha M
authors.initials: MM
authors.lastname: Téllez-Rojo
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D015415:Biomarkers / Q000652:urine; D001862:Bone Resorption / Q000150:complications / Q000517:prevention & control*; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000201:enzymology; D002136:Calcium, Dietary / Q000008:administration & dosage*; D024042:Collagen Type I / Q000652:urine; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008800:Mexico; D010455:Peptides / Q000652:urine; D010919:Placebos; D049590:Postpartum Period; D011247:Pregnancy; D011248:Pregnancy Complications / Q000517:prevention & control*; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; D002136:Calcium, Dietary; D024042:Collagen Type I; D010455:Peptides; D010919:Placebos; C052929:collagen type I trimeric cross-linked peptide; D000469:Alkaline Phosphatase