title: Calcium intake in winter pregnancy attenuates impact of vitamin D inadequacy on urine NTX, a marker of bone resorption.
abstract: OBJECTIVE
  Pregnancy is characterised by increased bone turnover, but high bone turnover with resorption exceeding formation may lead to negative maternal bone remodelling. Recent studies are conflicting regarding the effect of calcium on skeletal health in pregnancy. The aim of this study was to examine the seasonal effect of serum 25-hydroxyvitamin D (25OHD) and dietary calcium on a marker of bone resorption.
  
  
  METHODS
  This was prospective study of 205 pregnant women [two cohorts; early pregnancy at 13 weeks (n = 96), and late pregnancy at 28 weeks (n = 109)]. Serum 25OHD and urine cross-linked N-telopeptides of type I collagen (uNTX) were measured at both time points. Intakes of vitamin D and calcium were recorded using 3-day food diaries at each trimester.
  
  
  RESULTS
  Compared to summer pregnancies, winter pregnancies had significantly lower 25OHD and significantly higher uNTX. Higher calcium intakes were negatively correlated with uNTX in winter, but not summer. In late pregnancy, compared to those reporting calcium intakes ≥1000 mg/day, intakes of <1000 mg/day were associated with a greater increase in uNTX in winter pregnancies than in summer (41.8 vs. 0.9%). Increasing calcium intake in winter by 200 mg/day predicted a 13.3% reduction in late pregnancy uNTX.
  
  
  CONCLUSIONS
  In late pregnancy, during winter months when 25OHD is inadequate, intakes of dietary calcium <1000 mg/day were associated with significantly increased bone resorption (uNTX). Additional dietary calcium is associated with reduced bone resorption in late pregnancy, with greater effect observed in winter. Further research regarding optimal dietary calcium and 25OHD in pregnancy is required, particularly for women gestating through winter.
authors.affiliation: UCD Perinatal Research Centre, UCD Obstetrics and Gynaecology, School of Medicine, National Maternity Hospital, University College Dublin, Dublin, Ireland.
authors.forename: Eileen C
authors.initials: EC
authors.lastname: O'Brien
authors.affiliation: Department of Clinical Chemistry, St Vincent's University Hospital, Dublin, Ireland.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Kilbane
authors.affiliation: UCD Perinatal Research Centre, UCD Obstetrics and Gynaecology, School of Medicine, National Maternity Hospital, University College Dublin, Dublin, Ireland.|Department of Endocrinology, St Vincent's University Hospital, Dublin, Ireland.|UCD School of Medicine, National Maternity Hospital, University College Dublin, Dublin, Ireland.
authors.forename: Malachi J
authors.initials: MJ
authors.lastname: McKenna
authors.affiliation: Centre for Support and Training in Analysis and Research (CSTAR), School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Segurado
authors.affiliation: UCD Perinatal Research Centre, UCD Obstetrics and Gynaecology, School of Medicine, National Maternity Hospital, University College Dublin, Dublin, Ireland.
authors.forename: Aisling A
authors.initials: AA
authors.lastname: Geraghty
authors.affiliation: UCD Perinatal Research Centre, UCD Obstetrics and Gynaecology, School of Medicine, National Maternity Hospital, University College Dublin, Dublin, Ireland. fionnuala.mcauliffe@ucd.ie.
authors.forename: Fionnuala M
authors.identifier: http://orcid.org/0000-0001-6187-4017
authors.initials: FM
authors.lastname: McAuliffe
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D015415:Biomarkers / Q000097:blood / Q000652:urine; D001862:Bone Resorption / Q000209:etiology / Q000517:prevention & control*; D002112:Calcifediol / Q000097:blood; D002136:Calcium, Dietary / Q000627:therapeutic use*; D015331:Cohort Studies; D003094:Collagen / Q000652:urine*; D015930:Diet Records; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D039382:Maternal Nutritional Physiological Phenomena; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology* / Q000652:urine; D011261:Pregnancy Trimester, First; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D012306:Risk; D012621:Seasons; D012720:Severity of Illness Index; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology* / Q000652:urine
chemical_list: D015415:Biomarkers; D002136:Calcium, Dietary; C461299:urinary N-telopeptide of type I collagen, human; D015652:25-Hydroxyvitamin D 2; D003094:Collagen; D002112:Calcifediol
keywords: 25OHD; Bone turnover; Calcium; Pregnancy; Season; Vitamin D