Researchers recommend pregnant women take 4,000 IU vitamin D a day

In the 1950s and '60s, people were concerned that vitamin D could cause birth defects, according to Carol L. Wagner, MD, lead author of the study and a pediatric researcher at Medical University of South Carolina. It now is known that vitamin D is important for maternal and infant health, including bone health and immune function.

Recent studies have shown that vitamin D deficiency during pregnancy is a serious public health issue.

"Diet doesn't provide enough vitamin D, and we don't go in the sun as much as we need," Dr. Wagner said.

Therefore, she and her colleagues, including Bruce W. Hollis, PhD, who has worked in the field of vitamin D research for the last 30 years, set out to determine the optimal dose of vitamin D supplements for pregnant women without doing harm.

Researchers randomized 494 pregnant women at 12-16 weeks' gestation into three treatment groups. Group one received 400 International Units (IU) of vitamin D a day until delivery; group two received 2,000 IU and group three received 4,000 IU. The women were evaluated monthly to ensure safety.

"No adverse events related to vitamin D dosing were found in any of the three arms of the study," Dr. Wagner said.

Investigators also looked at the effects of vitamin D supplementation on complications during pregnancy, including preeclampsia, gestational diabetes, infections, and preterm labor and birth.

"The spectacular part of the study was it showed women replete in vitamin D had lower rates of preterm labor and preterm birth, and lower rates of infection," Dr. Wagner said.

The greatest effects were seen among women taking 4,000 IU of vitamin D per day. Therefore, the researchers recommend this daily regimen for all pregnant women.