Vitamin D Supplementation May Have Varying Effects in Pregnancy

Pregnant women may benefit more from customized vitamin D supplement doses, as certain factors appear to influence the effectiveness of supplementation, according to study results published in the Journal of Clinical Endocrinology & Metabolism.¹

“It is critical for pregnant women to have sufficient levels of vitamin D for the health of their baby,” study author Nicholas C. Harvey, MA, MB, BChir, MRCP, PhD, professor of rheumatology and clinical epidemiology at the University of Southampton in the United Kingdom, said in a press release.² “Our study findings suggest that in order to optimize vitamin D concentrations through pregnancy, the supplemental dose given may need to be tailored to a woman’s individual circumstances, such as the anticipated season of delivery.”

Using data from the multicenter, double-blind, randomized, placebo-controlled Maternal Vitamin D Osteoporosis Study (MAVIDOS, ISRCTN registration number 82927713) trial, Dr Harvey and colleagues assessed 25-hydroxyvitamin D (25[OH]D) levels in 829 pregnant women who received early pregnancy ultrasounds at 1 of 3 hospitals in the United Kingdom.

At approximately 14 weeks’ gestation, women were randomly assigned to receive either 1000 IU/d of the vitamin D3 supplement cholecalciferol (n = 407) or placebo (n = 422). Levels of 25(OH)D, maternal anthropometry, health, and lifestyle were measured at the beginning of the study and repeated at 34 weeks’ gestation. The researchers gauged compliance via pill count at 19 and 34 weeks.

As expected, higher 25(OH)D levels were found in the cholecalciferol supplementation group vs the placebo group at 34 weeks’ gestation (57.7 nmol/L vs 43.1 nmol/L; P <.001).¹

Additionally, among women taking cholecalciferol, multiple linear regression analysis linked lower 25(OH)D levels at 34 weeks’ gestation with higher pregnancy weight gain (kg) from 14 to 34 weeks (β = –0.81; 95% CI, –1.39 to –0.22), lower compliance (%) with study medication (β = –0.28; 95% CI, 0.072-0.48), lower 25(OH)D (nmol/L) in early pregnancy (β = 0.28; 95% CI, 0.16-0.4), and delivery in summer vs winter (β = 10.51; 95% CI, 6.4-14.63).¹

“Our findings of varied responses to vitamin D supplementation according to individual attributes can be used to tailor approaches to prenatal care,” study author Cyrus Cooper, OBE, MA, DM, FRCP, FFPH, FMedSci, professor of rheumatology and clinical epidemiology at the University of Southampton’s MRC Lifecourse Epidemiology Unit, said in the release.² “This work will inform the development of strategies to enhance bone development across generations.”

Despite their findings, the researchers cited several study limitations, including the exclusion of women with 25(OH)D levels lower than 25 nmol/L or higher than 100 nmol/L, a predominantly white study population, and the lack of examination of genetic determinants of response to vitamin D supplementation.¹

“Future studies should aim to determine appropriate doses to enable consistent repletion of 25(OH)D during pregnancy, and our findings support the notion that clinical approaches to vitamin D repletion may be informed by individual characteristics. As such, personalized vitamin D supplementation advice might become part of future antenatal care,” the researchers wrote.

References

1. Moon RJ, Harvey NC, Cooper C, et al. Determinants of the maternal 25-hydroxyvitamin D response to vitamin D supplementation during pregnancy. J Clin Endocrinol Metab. 2016 Oct 27. doi:10.1210/jc.2016-2869 [Epub ahead of print].
2. Customized vitamin D supplements may benefit pregnant women [press release]. Washington, DC: Endocrine Society Newsroom; October 27, 2016. https://www.endocrine.org/news-room/current-press-releases/customized-vitamin-d-supplements-may-benefit-pregnant-women. Accessed October 31, 2016.