Research on vitamin D is exploding, and we are learning that sufficient blood levels of this vitamin are crucial to our health, and also that a significant proportion of the population, including pregnant women, is deficient. Vitamin D is a key factor in fetal bone growth during the third trimester. For pregnant and nursing women, vitamin D insufficiency increases the risk of preeclampsia and also puts their children at risk of impaired growth during infancy and autoimmune diseases during childhood.1
Despite these dangers, vitamin D deficiency is common, affecting up to 50% of pregnant women and breastfed infants.1 Most prenatal vitamins, similar to other conventional multivitamins, contain only 400 IU vitamin D, an amount that is known throughout the scientific community to be inadequate for maintaining sufficient blood levels of vitamin D.
The National Institutes of Health considers 2000 IU to be the daily tolerable upper limit of vitamin D intake, but scientists wanted to know whether higher doses would be safe for pregnant women, and more importantly, whether using higher doses to attain sufficient blood levels of vitamin D would reduce the risk of pregnancy complications.
Researchers tested 400, 2000, and 4000 IU doses of vitamin D in pregnant women starting at 12 weeks gestation. They saw significant differences between groups in blood levels of vitamin D (25(OH)D). In healthy adults, a minimum of 30 ng/ml 25(OH)D is thought to be required for vitamin D to properly exert its many vital functions in the body.2 Consequently, I recommend that levels be maintained in the range of 35-55 ng/ml. The 400 IU group maintained 25(OH)D levels of only about 30 ng/ml, and the 2000 IU group reached 25(OH)D of 42 ng/ml by the end of their pregnancies. The 4000 IU group’s levels reached the optimal range earlier on in pregnancy and remained between 40 and 50 ng/ml for the duration of the study. Since there were no differences in any safety measures, and no adverse events were attributed to the supplements, the researchers concluded that vitamin D supplementation of up to 4000 IU is safe for pregnant women.3
The researchers then looked at pregnancy outcomes – whether the vitamin D affected pregnancy complications such as pre-term labor, pre-term birth, and infection.
The risk of these pregnancy complications overall was 50% lower in the 4000 IU group than the 400 IU group. Women who had complications on average had lower 25(OH)D levels than women who did not have complications. Importantly, neonatal serum 25(OH)D correlated with maternal 25(OH)D, confirming that the additional vitamin D helped to insure that babies were born with sufficient vitamin D levels.4
As mentioned above, I recommend that 25(OH)D levels be maintained in the range of 35-55 ng/ml. These authors recommend serum 25(OH)D levels of at least 40 ng/ml, and therefore supplementation level of 4000 IU according to their results. However, the level of supplementation necessary for individuals to reach optimal serum 25(OH)D levels may vary. Vitamin D needs of individual pregnant women should be assessed by blood test and supplementation should be adjusted accordingly. For some women that may be 2000 IU, but others may require more. I will continue to monitor these studies, and update my recommendations accordingly.
1. Mulligan ML et al. Implications of vitamin D deficiency in pregnancy and lactation. Am J Obstet Gynecol. 2009 Oct 19. [Epub ahead of print]
2. Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences.Am J Clin Nutr 2008;87(suppl):1080S– 6S.
3. Wagner CL et al. "Vitamin D supplementation during Pregnancy Part I NICHD/CTSA Randomized Clinical Trial (RCT): Safety Considerations" PAS 2010; Abstract 2630.7.
4. Wagner CL et al. "Vitamin D supplementation during Pregnancy Part 2 NICHD/CTSA Randomized Clinical Trial (RCT): Outcomes" PAS 2010; Abstract 1665.6
MedPageToday: PAS: Vitamin D Cuts Risks of Pregnancy. Michael Smith, North American Correspondent, MedPage Today May 01, 2010