Maternal obesity and baseline vitamin D insufficiency alter the response to vitamin D supplementation: a double blind, randomized trial in pregnant women

Raghad Alhomaid, Maria S Mulhern, JJ Strain, Eamon Laird, Martin Healy, Michael J. Parker, M McCann

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Background The achievement of target 25-hydroxyvitamin D [25(OH)D] concentrations in pregnancy may be altered by maternal obesity. Objective The authors examined the effects of maternal supplementation of 10 μg compared with 20 μg vitamin D3/d on maternal and umbilical cord 25(OH)D. The secondary aim was to investigate the influence of maternal BMI (in kg/m2) on the response of the primary outcomes. Methods The authors performed a 2-arm parallel double-blind randomized trial with 240 pregnant women recruited throughout the year in Northern Ireland. Women were stratified by BMI to receive 10 or 20 µg vitamin D3/d from 12 gestational wk (GW) until delivery. Maternal blood samples collected at 12, 28, and 36 GW and from the umbilical cord were analyzed for total serum 25(OH)D. A total of 166 women completed the study. Results Mean ± SD 25(OH)D at 36 GW was 80.8 ± 28.2 compared with 94.4 ± 33.2 nmol/L (P < 0.001) (10 compared with 20 µg vitamin D3/d, respectively). In those classified with 25(OH)D <50 nmol/L at baseline and assigned 10 µg vitamin D3/d, mean 25(OH)D concentrations remained <50 nmol/L at 36 GW, whereas those <50 nmol/L at baseline and assigned 20 µg vitamin D3/d, had mean 25(OH)D concentrations ≥50 nmol/L at 28 and 36 GW. In women with obesity and 25(OH)D <50 nmol/L at baseline, the related mean umbilical cord 25(OH)D was deficient (<25 nmol/L) in both treatment groups, whereas those with obesity and 25(OH)D ≥50 nmol/L at baseline had an average umbilical cord 25(OH)D between 25 and 50 nmol/L in both treatment groups. Conclusions Supplementation of 20 µg vitamin D3/d is needed to attain maternal and umbilical cord 25(OH)D concentrations ≥50 nmol/L on average, in those who start pregnancy with low 25(OH)D concentrations (<50 nmol/L). Under current recommendations, women with obesity and low 25(OH)D in early pregnancy are particularly vulnerable to maintaining a low 25(OH)D concentration throughout pregnancy and having an infant born with deficient 25(OH)D concentrations. This trial was registered at as NCT02713009.
Original languageEnglish
Article numbernqab112
Pages (from-to)1208-1218
Number of pages11
JournalThe American Journal of Clinical Nutrition
Issue number3
Early online date8 May 2021
Publication statusPublished (in print/issue) - 1 Sept 2021

Bibliographical note

© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.


  • Maternal obesity
  • Body weight
  • BMI
  • Pregnancy
  • 25(OH)D concentration
  • vitamin D
  • vitamin D requirements


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