Women who take large doses of vitamin D during pregnancy may be giving their children a lower risk of dental problems.

In a double-blinded clinical trial, researchers randomized 623 women to two groups. Beginning in the 24th week of pregnancy, one group took two pills daily, one containing 400 units and the other 2,400 units of vitamin D. The other took a 400 unit pill plus an identical-looking placebo. The study is in JAMA Pediatrics.

Six years later, the children were examined by dentists who did not know which mothers had taken the supplements. They found that children of women who took the vitamin D regimen had a 47 percent lower rate of enamel defects in both permanent and baby teeth than those in the control group.

At age 6, there was no association with cavities, “but you can’t have cavities without first having enamel defects. This is an extremely robust finding, and I have no doubt that it does not come by chance,” said the senior author, Dr. Hans Bisgaard, a professor of pediatrics at the University of Copenhagen. “By age 10, we will see plenty of cavities and this same protective effect,” he predicted.

Vitamin D is known to be essential in enamel development, but, the authors write, little is known about the cause or prevention of enamel defects. So this intervention, which had no adverse side effects, could be an effective measure.