Ask your OB/GYN for a simple vitamin D blood test, and supplement accordingly to bring your levels up.

If you're low on D, careful sun exposure can help. But supplements are a must.

RODALE NEWS, EMMAUS, PA—Medical students have long been taught that prescribing higher vitamin D supplement doses during pregnancy is dangerous, thanks to experimental animal research done in the 1960s that suggested a harmful effect. But humans differ from lab animals, particularly it comes to vitamin D processes, it seems. "OBs were basically taught, 'You don't go near vitamin D in pregnancy,'" explains Bruce Hollis, PhD, professor of pediatrics at the Medical University of South Carolina, the coauthor of a recent study on the topic. Much of the nation is suffering from vitamin D deficiency, but low levels of the vitamin have been linked to everything from certain cancers to dementia. Many doctors are still wary of prescribing higher-dose supplements to raise blood levels of the vitamin, particularly in pregnant women. But emerging research presented earlier this month at the Pediatric Academic Societies annual conference found that supplementing with higher doses of vitamin D in expectant mothers actually produced better pregnancy outcomes—fewer premature births and infections. In the hundreds of women studied, no adverse outcomes were linked to the higher vitamin D doses. "The low amount of vitamin D [400 International Units, or IU; 200 IU for pregnant women] that was set 50 years ago was never set scientifically. There was no science behind it; just intuition," says Hollis. "It's a reasonable level for an infant, but left adults totally in peril."

THE DETAILS: New research looking at vitamin D in pregnancy was partially funded by the National Institutes of Health, and women were very closely monitored for negative health impacts during the study because of the previous animal research mentioned above. In one of the studies, researchers divided pregnant women into three groups, one that received 400, one 2,000, and a third that took 4,000 IU of vitamin D a day, from the time they were three months pregnant through delivery. (Urinary calcium levels were monitored regularly—elevated levels are the most common side effect of high-dose vitamin D supplementing. However, no abnormal levels were reported during the study.) In the studies, researchers found that taking 4,000 IU (about 10 times the amount normally recommended by many health agencies and medical groups) cut the rate of pregnancy-related complications (including gestational diabetes, high blood pressure, and preeclampsia) in half when compared to the women who took just 400 IU a day every day. Before the study, researchers found that nearly all the black women, more than 65 percent of the Hispanic women, and about half of the white women were vitamin D-deficient. (Skin manufactures vitamin D when sunlight hits it during the warm-weather months, but it's harder for this process to occur in darker-skinned people.) Authors of the new studies concluded that all pregnant women should take 4,000 IU of vitamin D a day during pregnancy to adequately raise blood levels of the vitamin in the mother. Hollis, citing preliminary research on vitamin D in nursing mothers, also recommends that lactating mothers take 6,000 IU to raise blood levels adequately and provide levels adequate for breastfeeding babies.

WHAT IT MEANS: Researchers don't even know everything vitamin D does in our body, but they know it plays a strong role in regulating the human immune system. This research suggests it's particularly important in pregnancy, perhaps because an out-of-check immune system could increase the odds of complications, including preeclampsia and infections. "Vitamin D early on makes the adaptive system suppressed, so antibodies don't go after the fetus," explains Hollis.