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Vitamin D Supplements Safe For Pregnant Women, Offer Benefits


Although pregnant women are typically warned against taking various supplements, a new study has found that vitamin D supplements are safe for both women and their newborns, even when taken at high amounts. This study is the first to test a vitamin D supplement at 4,000 IU, the upper level set by the Institutes of Medicine (IOM), in pregnant women.

Vitamin D offers benefits for pregnant women

The debate over safe and effective levels of vitamin D for various populations, and especially pregnant women, has been a long, ongoing one. Dr. Bruce Hollis, from the Medical University of South Carolina in Charleston, who led the new study, noted that “the scientific debate has made little progress since Dr. Gilbert Forbes made a recommendation of 200 IU (international units) per day in 1963, which was based on a hunch.”

In 1997, the IOM stated that 200 IU of vitamin D during pregnancy was adequate, and that anything greater than 2,000 IU daily could cause harm. Recently, however, the IOM modified its stance by increasing the tolerable upper intake limit to 4,000 IU, but still maintained a low estimated average requirement of 400 to 600 IU daily, which, as the authors of the new study note, is based on old data even though new data exist.

The randomized, controlled trial enrolled 502 healthy pregnant women between 12 and 16 weeks into gestation to determine how different dosages of vitamin D daily could safely sustain a circulating level of at least 32 nanograms per milliliter of 25(OH)D (the form of vitamin D in blood serum). A total of 350 women completed the study through delivery.

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The women were randomly assigned to one of three treatment groups: 400 IU, 2,000 IU, or 4,000 IU of vitamin D daily. A balance of Caucasian, Hispanic, and African-American women were in each group. Analysis by the researchers revealed that women who took 4,000 IU per day of vitamin D were more likely to achieve and maintain the desired level of 25(OH)D throughout their pregnancy, while women who took lower doses of the supplement did not reach the desired level.

In addition, 4,000 IU of vitamin D was found to be safe. As Dr. Hollis noted, “a daily dosage of up to 4,000 IU of vitamin D was required to sustain normal metabolism in pregnant women,” and that “following decades of speculation into its safety our research has demonstrated vitamin D supplementation to be both safe and effective.”

Previous research has indicated that a pregnant woman’s vitamin D status is important not only for her own health but for that of her unborn child as well. For example, a study published in the Journal of Clinical Endocrinology and Metabolism in 2010 reported that vitamin D status in pregnant women affects the bone mineral accumulation and bone size of the fetus.

In a more recent study, researchers noted that pregnant women who take vitamin D supplements may protect their newborns against respiratory syncytial virus (RSV), a potentially fatal disease. Another study, published in Epidemiology, reported that vitamin D supplementation during pregnancy may reduce a mother’s risk of developing preeclampsia. Vitamin D is also known to play a role in maintaining the body’s internal regulation (homeostasis) during pregnancy.

Overall, this latest study shows that 4,000 IU of vitamin D supplements taken by pregnant women are safe and effective for both women and their newborns regardless of race. The authors concluded that their findings suggest the IOM raise their current recommendations for vitamin D for pregnant women “to 4,000 IU vitamin D per day so that all women regardless of race attain optimal nutritional and hormonal vitamin D status throughout pregnancy.”

Belderbos ME et al. Pediatrics 2011 May 9; doi:10.1542/peds.2010-3054
Haugen M et al. Epidemiology 2009 Sept; 20(5): 720-26
Hollis B et al. Journal of Bone and Mineral Research 2011 June; doi: 10.1002.jbmr.463
Vijakainen HT et al. Journal of Clinical Endocrinology and Metabolism 2010 Apr; 95(4): 1749-57