Vitamin D Found to Be Safe for Healthy Pregnant Women

Laurie Barclay, MD

July 06, 2011

July 6, 2011 — Vitamin D supplementation of 4000 IU/day is safe and effective for healthy pregnant women and their infants, according to the results of a large, double-blinded, randomized clinical trial published online June 27 in the Journal of Bone & Mineral Research.

"Vitamin D supplementation during pregnancy remains controversial largely due to severe misconceptions about the potential harm it may cause to the fetus," lead author Bruce W. Hollis, PhD, from the Division of Neonatology, Department of Pediatrics, Medical University of South Carolina in Charleston, said in a news release. "Surprisingly 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."

Women with a singleton pregnancy were randomly assigned to receive 400, 2000, or 4000 IU vitamin D3/day beginning at 12 to 16 weeks' gestation and continuing until delivery. Maternal and neonatal circulating 25(OH)D at delivery was the main study endpoint, and secondary endpoints were achievement of 25(OH)D level of 80 nmol/L or more and 25(OH)D concentration required to achieve maximal 1,25(OH)2D production.

The study completion rate (continuation until delivery) was 350 of 494 women enrolled. The supplementation groups varied significantly in mean 25(OH)D at delivery and 1 month before delivery (P < .0001), as well as in the proportion of participants who were vitamin D sufficient (P < .0001). These were greatest in the group receiving 4000 IU.

For the 2000 IU group compared with the 400 IU group, the relative risk (RR) for achieving more than 80 nmol/L 25(OH)D within 1 month of delivery was significantly different (RR, 1.52; 95% confidence interval [CI], 1.24 - 1.86). This was also true for the 4000 IU group compared with the 400 IU group (RR, 1.60; 95% CI, 1.32 - 1.95), but not for the 4000 IU group compared with the 2000 IU group (RR, 1.06; 95% CI, 0.93 - 1.19).

There was a direct effect of circulating 25(OH)D on circulating 1,25(OH)2D concentrations throughout pregnancy (P < .0001), with the 4000 IU group having the highest production of 1,25(OH)2D in all strata.

"The study is a large, double-blinded, randomized clinical trial, showing that supplementation with vitamin D in a dose of 2000 IU and 4000 IU per day is safe and without any side effects during pregnancy," Kristine Møller, PhD, from the Department of Medicine and Endocrinology, Aarhus University Hospital in Denmark, told Medscape Medical News when asked for independent comment.

"Women with low 25(OH)D at baseline, mainly women with an African-American background, had the largest benefit of the supplementation."

The study authors note that the current estimated average requirement was comparatively ineffective at achieving adequate circulating 25(OH)D, especially in blacks, but that vitamin D supplementation of 4000 IU/day for pregnant women was most effective in achieving sufficiency in all women and their neonates, regardless of race

Safety measures did not differ among groups, and no adverse event was thought to be caused by vitamin D supplementation or circulating 25(OH)D levels.

"The study did not find any advantage of vitamin D supplementation on the risk of adverse pregnancy outcome, risk of cesarean section, or in respect to size of the newborn child," Dr. Møller said. "This could be due to the relative low number of women who, because of their low 25(OH)D levels at baseline, did benefit from the supplementation. Of future interest would be to explore the effect of vitamin D supplementation in relation to the risk of adverse pregnancy outcome, risk of cesarean section, or in respect to size of the newborn child in vitamin D–deficient women."

Limitations of this study include the possible lack of generalizability to women living at other latitudes or to those with preexisting hypertension and diabetes, and the inability to determine the safety of vitamin D supplementation before the twelfth week of gestation.

"In our study subjects, a daily dosage of up to 4,000 IU of vitamin D was required to sustain normal metabolism in pregnant women," Dr. Hollis concluded. "Furthermore, following decades of speculation into its safety our research has demonstrated vitamin D supplementation to be both safe and effective."

On the basis of their findings, the investigators suggest that "the current vitamin D EAR and RDA for pregnancy women issued in 2010 by the Institute of Medicine should be raised 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."

The National Institute of Child Health and Human Development and National Institutes of Health/National Center for Research Resources supported this study. The study authors and Dr. Møller have disclosed no relevant financial relationships.

J Bone Mineral Res. Published online June 27, 2011. Full text

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