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Prenatal multivitamins provide uneven source of iodine

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October 23, 2018

Nearly one-quarter of the best-selling prenatal multivitamins in the U.S. in 2016 and 2017 did not contain iodine, although most of those that included iodine contained the recommended amount per dose, according to research published in Thyroid.

“Despite iodine sufficiency in the general U.S. population, the high variability of iodine content in food sources and differences in dietary patterns may leave some populations at risk for iodine deficiency,” Elizabeth N. Pearce, MD, MSc, FACE, associate professor of medicine in the section of endocrinology, diabetes and nutrition at Boston University School of Medicine, and colleagues wrote. “In particular, mild iodine deficiency has recently re-emerged among pregnant U.S. women.”

The researchers ascertained information on both adult and prenatal multivitamins from the market research company Information Resources. Eighty-nine of the best-selling adult multivitamins and 59 prenatal multivitamins from July 2016 to July 2017 were included in the analysis. Iodine levels were determined based on the labels of each product. Sales numbers during the study period excluded direct selling, specialty store and internet sales.

Of the 89 adult multivitamins, 74.2% included at least some iodine, with 75.8% of those providing the daily amount recommended by the American Thyroid Association (150 µg), according to the researchers. Nearly 9 billion doses of adult multivitamins were sold during the study period, and 84.8% contained iodine, whereas 78% had the recommended amount.

Of the 59 prenatal multivitamins, 57.6% contained iodine. Nearly all prenatal vitamins with iodine (91.2%) contained more than 150 µg per dose, which met ATA’s recommendation for pregnant women, the researchers wrote. Of the more than 460 million doses of prenatal multivitamins that were sold, 76.8% had iodine and 75.9% met the required amount.

Despite a median of 150 µg per dose for both the adult and prenatal multivitamins groups, both had wide ranges of iodine content. Prenatal vitamins also relied on a variety of iodine sources, with 73.5% of those with iodine made from potassium iodide. Kelp (23.5%) and the inactivated yeast Saccharomyces cerevisiae (2.9%) made up the rest, according to the data. All adult multivitamins in the study were produced with potassium iodide as the iodine source.

“Our results demonstrate that multivitamins are used by a substantial proportion of the

population and can be an important source of iodine for pregnant women,” the researchers wrote. “Some [prenatal multivitamins] used kelp and inactivated yeast as sources of iodine, although these were not employed in any of the [adult multivitamins] products. These sources have been previously shown to be variable in their iodine content. While it is unclear why [prenatal multivitamins] were less likely to use potassium iodide as an iodine source than [adult multivitamins], it is possible that kelp or inactivated yeast may be seen as more appropriate for those [prenatal multivitamins] that were marketed as ‘natural’ or ‘organic.’” – by Phil Neuffer

Disclosures: The authors report no relevant financial disclosures.

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This is an important study which provides an update to the situation regarding the iodine content of multivitamin products formulated for pregnant and non-pregnant individuals sold in the U.S. As adequate iodine nutrition is a well-established public health measure that can protect against preventable lifelong mental impairments, I am glad that the investigators report these new data to better understand this critical issue.

It was encouraging to see that nearly all (91%) of the prenatal products sold during the study period contained the minimal recommended level of iodine (150 mcg/day), due to the concerted efforts by the Council on Responsible Nutrition, American Thyroid Association, Endocrine Society and American Academy of Pediatrics to establish recent recommendations on this topic. However, the major primary findings, that there remains a wide range of iodine content in U.S. adult multivitamins and prenatal vitamins and that 24% of the prenatal vitamin doses sold (nearly 500 million in 2016-2017) still did not include any iodine, are striking. The results highlight the ongoing need to particularly protect against the harms of iodine insufficiency among those most vulnerable — women taking vitamins during the preconception period, pregnancy and the post-partum period.

Angela M. Leung, MD, MSc

Assistant Professor of Medicine,
Division of Endocrinology, Diabetes and Metabolism,
UCLA David Geffen School of Medicine, VA Greater Los Angeles Healthcare System

Disclosure: Leung reports that she serves on the board of directors of the American Thyroid Association.