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Pregnancy-related changes in bone turnover markers are not accompanied by mineral mobilisation in the appendicular skeleton in women with habitually low calcium intake

Published online by Cambridge University Press:  30 April 2021

M. Breasail ,
K. A. Ward ,
L. M. A. Jarjou ,
S. E. Moore  and
A. Prentice
M. Breasail
Affiliation:
MRC Nutrition and Bone Health Research Group, Cambridge, UK
K. A. Ward
Affiliation:
MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, UK MRC Unit The Gambia, London School of Hygiene and Tropical Medicine, Banjul, Gambia
L. M. A. Jarjou
Affiliation:
MRC Unit The Gambia, London School of Hygiene and Tropical Medicine, Banjul, Gambia
S. E. Moore
Affiliation:
MRC Unit The Gambia, London School of Hygiene and Tropical Medicine, Banjul, Gambia Department of Women and Children's Health, King's College London, London, UK
A. Prentice
Affiliation:
MRC Nutrition and Bone Health Research Group, Cambridge, UK MRC Unit The Gambia, London School of Hygiene and Tropical Medicine, Banjul, Gambia
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Proceedings of the Nutrition Society , Volume 80 , Issue OCE1: Winter Conference Live 2020, 8–9 December 2020, Micronutrient malnutrition across the life course, sarcopenia and frailty , 2021 , E22
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In pregnancy, changes in maternal calcium (Ca) economy occur to satisfy fetal Ca demand(Reference Prentice1). Whether maternal mineral reserves facilitate these requirements in a population with habitually low Ca intakes (~400mg/day)(Reference Prentice2) is difficult to quantify and no data exist from sub-Saharan Africa. Our aim was to determine whether changes in maternal bone metabolism occurred in pregnancy using bone turnover markers (BTMs) and peripheral quantitative computed tomography (pQCT) between early second and third trimesters.

Pregnant rural Gambians aged 18–45 years (n = 467) participating in a trial of antenatal nutritional supplements (ISRCTN49285450)(Reference Moore3) were invited for longitudinal measurements: biochemistry including maternal BTMs (serum collagen type 1 cross-linked β-C-telopeptide (CTX), type 1 procollagen N-terminal (P1NP) plus parathyroid hormone (PTH) and 1,25(OH)2D)) and pQCT scans at the non-dominant radius and tibia. pQCT measures were total volumetric bone mineral density (vBMD), trabecular vBMD, total area at distal sites (4%) and cortical vBMD, bone mineral content (BMC), total area at proximal sites (33/38%). Supplements were iron folic acid (IFA; standard care), multiple micronutrients (MMN), protein energy (PE), PE + MMN. Independent t-tests tested whether within-group and pooled change differed significantly from 0. Multiple regression adjusting for age, and then supplement group tested if between-visit change differed by group. Data for change are expressed as mean [95CI]%.

Visits occurred at mean (SD) 14(3) and 31(1) weeks of pregnancy. Pregnancy-related changes in BTMs were observed with CTX increasing by 23.0 [15.09,29.29]% and P1NP decreasing by 32.4 [-37.19,-28.17]%. Changes in maternal PTH and 1,25(OH)2D were also evident, increasing by 13.2 [8.44,19.34]% and 21.0 [17.67,24.29]% respectively. No significant group differences were seen. Radial trabecular and cortical vBMD, and BMC increased between visits by 1.15 [0.55,1.75]%, 0.35 [0.26,0.44]% and 0.55 [0.41,0.68]% respectively. At the tibia, total and trabecular vBMD increased by 0.34 [0.15,0.54]% and 0.46 [0.17,0.74]%, while cortical vBMD and BMC increased by 0.41 [0.24,0.58]%, and 0.47 [0.25,0.69]% respectively. At the radius change in cortical vBMD in MMN and PE was 0.54 [-1.01, -0.07]% and 0.73 [-1.20,-0.26]% lower than IFA. Increase in radius cortical CSA in MMN was 0.67 [0.10,1.25]% greater than IFA. Change in tibia total vBMD was 0.76 [0.22,1.30]% greater in PE + MNN vs IFA.

Between-visit changes in BTMs suggest pregnancy-related changes in maternal bone mineral homeostasis. However, no evidence of bone mineral mobilisation was observed in the peripheral skeleton, rather modest increases were observed. No consistent differences were found by supplement group, despite the MMN groups containing vitamin D. In this population, with habitually low Ca intakes, the peripheral skeleton is not mobilised as a Ca source for the offspring.

However, in light of the large changes in BTMs it is possible that mobilisation was occurring at axial sites because BTMs in the circulation reflect changes throughout the skeleton.

References

Prentice, A. (2003) J Nutr, 133(5 Suppl 2): p. 1693s–1699s.CrossRefGoogle Scholar
Prentice, A. (1994) Adv Exp Med Biol, 352: p. 243–55.CrossRefGoogle Scholar
Moore, S.E., et al. (2012) BMC Pregnancy Childbirth, 12: p. 107.CrossRefGoogle Scholar