Iodine Content of the Best-Selling United States Adult and Prenatal Multivitamin Preparations

Iodine is essential for thyroid hormone production and fetal development. Even mild maternal iodine deficiency in gestation may be associated with impaired child neurodevelopment. Iodine requirements increase during pregnancy and lactation. Supplements containing 150 μg/day are recommended by the American Thyroid Association for all U.S. women who are pregnant, lactating, or planning pregnancy. The contribution of multivitamin supplements as an iodine source for pregnant and nonpregnant US adults has not been well studied. This study aimed to understand better the contribution of the top-selling adult multivitamins (AMV) and prenatal multivitamins (PMV) to iodine nutrition in the United States.Product names, dollar sales, unit and volume sales, and recommended daily intakes of the top-selling 99 AMV and 60 PMV from July 2016 to July 2017 were obtained from Information Resources, Inc. Iodine content and source were determined from product labels. After excluding private-label brands and unavailable product labels, a final sample of 89 AMV and 59 PMV was analyzed.Of the 89 AMV, 74.2% contained iodine. The median (range) iodine content of AMV was 150 μg (38-150 μg) per daily serving. Over the study period, 8,924,371,955 AMV doses were sold, of which 84.8% contained iodine. Thirty-four (57.6%) of the 59 PMV contained iodine, with a median (range) iodine content of 150 μg (25-290 μg) per daily serving. Over the study period, 466,927,559 PMV doses were sold, of which 76.8% contained iodine. All iodine-containing AMV used potassium iodine as an iodine source. Of iodine-containing PMV, 73.5% used potassium iodide, 23.5% kelp, and 2.9% inactivated Saccharomyces cerevisiae as an iodine source.During the one-year study period, a higher proportion of AMV doses than PMV doses contained iodine. Some PMV but no AMV included sources of iodine known to be highly variable. The median iodine content of the top-selling AMV and PMV was at the recommended 150 μg daily intake, but the range remains wide. Twenty-four percent of PMV doses sold did not contain iodine. More effort is needed to ensure adequate iodine content in prenatal vitamins for women who are pregnant, lactating, or planning pregnancy.