Vitamin D supplementation during pregnancy

Abstract

Vitamin D requirements have become one of the most highly debated and controversial topics in nutrition. Recommendations for vitamin D intake during pregnancy are a central part of this discussion. The publication of a controlled trial of vitamin D supplementation in pregnant women by Hollis and coworkers in this issue of JBMR provides important data about the effects of different doses of vitamin D3 supplementation on serum 25-hydroxyvitamin D [25(OH)D] levels. (1) Hollis and coworkers report that providing daily supplements of 2000 or 4000 IU of vitamin D3 during the second and third trimesters of pregnancy led to higher serum 25(OH)D concentrations in women during pregnancy and in their newborn infants than supplements of 400 IU/d. (1) As suggested by a footnote, further results from this controlled trial may be provided in the future in the peer-reviewed literature. For now, an evaluation of these results and how they might guide vitamin D recommendations during pregnancy is appropriate. In this report, (1) increases in both vitamin D supplementation and serum 25(OH)D level were associated with higher serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels. This outcome was the primary one for which this study was designed and sample size determined. However, there was no evidence of any clinical outcome differences based on supplement dose, and such outcomes were not part of the original study design. Specifically, there were no significant differences based on supplement dose in the 350 subjects who completed the study in C-section rate, gestational age, birth weight, or neonatal intensive-care unit (NICU) admission rate. Rates of preeclampsia and preterm birth based on supplement dose were not provided. Although NICU admission is not a complete assessment measure for neonatal outcome, these findings provide evidence that different levels of vitamin D supplementation had no significant positive or negative effect on the need for advanced neonatal care. Of note is that although an intention-to-treat analysis was indicated in the methods, outcome data are not available for the over 100 subjects who discontinued the study or were withdrawn from it without a known pregnancy loss. Outcomes such as neonatal or maternal bone mineral content, postneonatal infant health outcomes, and long-term bone outcomes for mother and infant are not provided in this report. (1) There is conflicting scientific evidence regarding the long-term effects of maternal vitamin D supplementation on childhood health outcomes (2,3) and no evidence about long- or short-term outcomes for maternal bone health from supplementation at doses of 4000 IU/d during pregnancy.