Prenatal Vitamins Should Contain Only Potassium Iodide, Not Other Sources Of Iodine, Scientists Urge

The researchers' recommendation appears as a research letter in the February 26th issue of the New England Journal of Medicine.

Normal thyroid function in fetuses and breastfed infants, which is dependent on sufficient maternal dietary intake of iodine, is crucial for normal neurocognitive development. Iodine deficiency affects more than 2.2 billion persons and is the leading cause of preventable mental retardation worldwide. Even mild iodine deficiency may have adverse effects on the cognitive function of children.

Using the Internet, the BUSM researchers identified 127 nonprescription and 96 prescription prenatal multivitamins currently marketed in the U.S. Of these multivitamins, 114 (87 nonprescription and 27 prescription) contained iodine. According to the label, 89 percent contained 150µg or more of iodine per serving. The iodine was in the form of kelp in 42 multivitamins, potassium iodide in 67, or another ingredient in five.

The researchers then measured the iodine content in 60 randomly selected iodine-containing prenatal multivitamins and compared the results with the values on their labels. They found that the iodine measured in those containing potassium iodide was approximately 75 percent of that stated on their labels. In contrast, the multivitamins containing kelp had large variations in their iodine content.

"The American Thyroid Associated has recommended that women receive prenatal vitamins containing 150µg of iodine daily during pregnancy and lactation. However, the iodine content of prenatal vitamins is not mandated in the United States," said author Elizabeth Pearce, MD, an assistant professor of medicine at BUSM, on behalf of her co-authors, Angela Leung, MD and Lewis Braverman, MD.

"In order to maintain consistency of labeling and to ensure these vitamins contain the recommended dosage, we strongly propose that the manufacturers of these products use only potassium iodide at a dose of 200µg per serving," she added.