A major new study of vitamin A has found that doses only slightly above the maximum recommended levels during the early stages of pregnancy significantly increase the risk of birth defects.
The results prompted researchers to recommend that women of child-bearing age consume vitamin A primarily from their diet, along with modest levels in multivitamin supplements.
Researchers had already known that moderately high intake of vitamin A, on the order of 25,000 International Units per day or more, causes severe birth defects. But the new results from the Boston University School of Medicine, based on a study of more than 22,000 pregnant women, indicate that any dose above 10,000 IU per day can carry some risk.
The danger increases steadily with intake, and women consuming 20,000 IU per day were about four times as likely to have a child with a birth defect as those consuming less than 10,000 IU according to the study, which is scheduled to be published in the New England Journal of Medicine in November.
The journal eased its normally stringent rules on prepublication release of results to allow the study to be publicized “because of the potential public health importance of the findings,” said its editor, Dr. Jerome P. Kassirer.
The study’s chief investigator, epidemiologist Kenneth J. Rothman, cautioned that many commercial multivitamins contain 10,000 IU of vitamin A, enough to push women into the dangerous range, and that some contain as much as 25,000 IU.
The findings “don’t really surprise me at all,” said John Hathcock of the Council for Responsible Nutrition, which represents vitamin manufacturers. CRN, he noted, has recommended since 1987 that pregnant women consume no more than 8,000 IU per day.
But Michelle Kling, a spokes woman for the March of Dimes Birth Defects Foundation noted that “Multivitamins are very important for pregnant women. They make up for (essential nutrients) that are not gotten from the diet.” The March of Dimes recommends taking multivitamins that contain no more than 5,000 IU of vitamin A and against taking supplements containing only vitamin A.
Virtually everyone agreed that there may be an easy way out of the dilemma: switching from supplements containing vitamin A to those containing beta-carotene, an antioxidant vitamin that is beneficial to the heart and that is converted to vitamin A in the body. It is also present in a variety of vegetables.