Iodine content of prenatal multivitamins in the United States.

To the Editor: Normal thyroid function in fetuses and breast-fed infants, which is dependent on sufficient maternal dietary intake of iodine, is crucial for normal neurocognitive development.1 Children of mothers with severe iodine deficiency may have cretinism. Iodine deficiency affects more than 2.2 billion persons (38% of the world’s population) and is the leading cause of preventable mental retardation worldwide.2 Even mild iodine deficiency may have adverse effects on the cognitive function of children.1 National surveys including the first and third National Health and Nutrition Examination Surveys (NHANES I and III) and NHANES 2001–2002 have reported a decrease of approximately 50% in adult urinary iodine values since the 1970s in the United States. In the subgroup of women of childbearing age, the median urinary iodine value decreased from 294 to 128 μg per liter. The most recent NHANES survey (2003–2004) reported that 37.2% of this subgroup of women had urinary iodine values below 100 μg per liter, which suggests mild iodine deficiency.3 The Institute of Medicine recommends a daily iodine intake of 220 μg during pregnancy and 290 μg during lactation; the World Health Organization recommends 250 μg of iodine daily for pregnant and lactating women. The American Thyroid Association has recommended that women receive prenatal vitamins containing 150 μg of iodine daily during pregnancy and lactation.4 However, the iodine content of prenatal multivitamins is not mandated in the United States. Using the Internet, we identified 127 nonprescription and 96 prescription prenatal multivitamins currently marketed in the United States. Of these multivitamins, 114 (87 nonprescription and 27 prescription) contained iodine; according to the product labeling, 101 (89%) contained 150 μg or more of iodine per daily dose. The iodine was in the form of kelp (in 42 multivitamins), potassium iodide (in 67), or another ingredient (in 5). We measured the iodine content in 60 randomly selected iodine-containing prenatal multivitamins (1 to 2 tablets per bottle, each from a single lot) and compared the results with the values on their labels (Table 1). The mean (±SE) level of measured iodine per daily dose in 35 potassium iodide–containing vitamins was 119.0±13.6 μg. Table 1. Iodine Content in Prenatal Multivitamins.