Seven out of every ten pregnant women in the United States are not getting enough Vitamin D according to a study published in the May issue of the American Journal of Obstetrics and Gynecology. While prenatal vitamins do raise Vitamin D levels during pregnancy, the study shows that higher doses may be needed for many women.

Adit Ginde, MD, MPH, from University of Colorado Denver School of Medicine, lead author of the study said, "We already know Vitamin D is important for bone health of the mother and infant, but we are just starting to scratch the surface about the many potential health benefits of Vitamin D during pregnancy."

The latest study shows that many pregnant women in the United States have insufficient vitamin D levels. For those women, prenatal vitamins do not provide enough vitamin D, and higher doses are needed to raise levels. Women with darker skin, those who cover their skin for religious or cultural reasons and those living further north during winter months are at particularly high risk for lower Vitamin D levels.

"Prenatal vitamins do help raise vitamin D levels, but many women start taking them after becoming pregnant. Although research is ongoing, I think it's best for women to start a few months before becoming pregnant to maximize the likely health benefits," said Ginde.

There is a growing body of evidence that Vitamin D levels have fallen below what's considered healthy in the overall population -- likely from decreased outdoor activity. And vitamin D has reemerged as an important nutritional factor in maternal and infant health. Vitamin D deficiency early in life has been linked to increased risk of respiratory infections and childhood wheezing. Lower levels in adults have been linked to cardiovascular disease and specific types of cancer.

The study did find that some women have enough Vitamin D. Study co-author Carlos Camargo, MD, DrPH, from Massachusetts General Hospital cautioned that there may be risks from excessive Vitamin D intake. "We need more data from clinical trials of Vitamin D supplementation in pregnant women. If the ongoing trials continue to show benefit, the best strategy will likely be measuring Vitamin D levels through a simple blood test and choosing supplementation doses according to those levels."

Ginde added, "This tailored approach is common in preventive care for people with high cholesterol, and safer and more effective than a one-size-fits-all solution."

The study team from University of Colorado School of Medicine, Massachusetts General Hospital and Children's Hospital Boston analyzed nationally representative data from 928 pregnant and 5,173 non-pregnant women of childbearing age collected by the Centers for Disease Control and Prevention. This research was supported by the National Institutes of Health.