Also, this study does not address the diet of the babies, Lawrence said. Although vitamin D is in both breast milk and infant formula, cholesterol and the amino acid taurine are only found in breast milk and also affect brain development after birth, she added.
Lawrence advises pregnant women get a dietary consultation in their first trimester and consider vitamin D supplementation. "We have realized that vitamin D has a lot more impact than to prevent rickets," she said.
Vitamin D may have additional benefits for mothers-to-be. Other research conducted by Hollis and his team found that pregnant women taking vitamin D could lower their risk of pregnancy-related diabetes and high blood pressure.
Early studies suggesting that high levels of vitamin D could lead to birth defects were bogus, Hollis said.
Women can receive up to 50,000 units a day before worrying about having too much vitamin D, Hollis said. Excessive vitamin D can lead to spikes in blood levels of calcium, which can, in turn, lead to kidney and nerve damage and abnormal heart rhythm.
To learn more about vitamin D, visit the Office of Dietary Supplements at the U.S. National Institutes of Health.
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