Women who take high doses of vitamin D during pregnancy have a greatly reduced risk of complications, including gestational diabetes, preterm birth, and infection, new research suggests.

Based on the findings, study researchers are recommending that pregnant women take 4,000 international units (IU) of vitamin D every day -- at least 10 times the amount recommended by various health groups.

Women in the study who took 4,000 IU of the vitamin daily in their second and third trimesters showed no evidence of harm, but they had half the rate of pregnancy-related complications as women who took 400 IU of vitamin D every day, says neonatologist and study co-researcher Carol L. Wagner, MD, of the Medical University of South Carolina.

Wagner acknowledges the recommendation may be controversial because very high doses of vitamin D have long been believed to cause birth defects.

"Any doctor who hasn't followed the literature may be wary of telling their patients to take 4,000 IU of vitamin D," she says. "But there is no evidence that vitamin D supplementation is toxic, even at levels above 10,000 IU."