Iodine in Prenatal Vitamins

Pregnant woman holding belly, outdoors, mid section
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Pregnant women — and in particular, pregnant women with thyroid conditions — need extra iodine. Iodine is necessary because it is a building block for the body's manufacture of thyroid hormone. During the first trimester of pregnancy, when a fetus is unable to produce thyroid hormone, the mother produces "thyroid hormone for two," so to speak. If she does not have enough iodine in her system, the health of her infant — and her own health — may suffer due to a lack of sufficient thyroid hormone.

While iodine deficiency has not been an issue in the United States, it is on the rise. In late 2006, the Public Health Committee of the American Thyroid Association (ATA) issued a statement in the journal Thyroid calling for all pregnant women to supplement with iodine. And the 2003–2004 National Health and Nutrition Examination Surveys (NHANES) study found that more than 37% of women of childbearing age have urinary iodine values suggesting mild iodine deficiency.

Recommended Levels of Iodine

Concerns over iodine deficiency during pregnancy and lactation (breastfeeding) have resulted in a number of organizations issuing guidelines and recommendations for iodine intake. According to the New England Journal of Medicine (NEJM), these are the recommended levels of daily iodine intake during pregnancy and lactation:

  • Daily iodine intake of 220 µg during pregnancy and 290 µg during lactation — The Institute of Medicine
  • Daily iodine intake of 250 µg for pregnant and lactating women — The World Health Organization
  • Vitamin with iodine level of 150 µg for pregnant and lactating women — The American Thyroid Association

The 2011 Guidelines for Thyroid Disease in Pregnancy also recommend iodine supplementation during pre-conception, pregnancy and while breastfeeding.

While many women assume that prenatal vitamins have all the key nutrients needed by a pregnant woman, the iodine content of prenatal multivitamins sold in the United States is not mandated. That means that prenatal vitamins have varying levels of iodine content, and because the iodine in them can come from different sources, they often deliver an actual level of iodine that differs from the stated potency.

The NEJM reported on an evaluation that looked at 127 non-prescription and 96 prescription prenatal multivitamins currently marketed in the United States. Of these multivitamins, 114 (87 nonprescription, 27 prescriptions) contained iodine. Overall, only about half the vitamins evaluated contained iodine, with 32% of non-prescription prenatal vitamins containing no iodine whatsoever, and a whopping 72% of the prescription prenatal vitamins studied had no iodine.

Among those that did include iodine, 89% contained 150 µg or more of iodine per daily dose. Most got their iodine from kelp or potassium iodide. The researchers evaluated the iodine content in 60 of the prenatal vitamins with iodine and found that generally, for vitamins with potassium iodine, the iodine content was approximately equivalent to 76% of the total potassium iodide content. The kelp did not deliver reliable iodine levels, however, and varied by as much as 50% from the stated levels. Ten brands had iodine values that delivered less than half the stated iodine level.

According to the experts, to meet the minimum guidelines of 150 µg for pregnant and lactating women recommended by the American Thyroid Association, manufacturers of prenatal multivitamins in the United States should be encouraged to include iodine — but only in the more reliable potassium iodide form — and to include at least 197 µg of potassium iodide per daily, which will ensure that these vitamins contain 150 µg of supplemental daily iodine.

In 2015, the US Council for Responsible Nutrition's called for "all dietary-supplement manufacturers and marketers to begin including at least 150 μg of iodine in all daily multivitamin/mineral supplements intended for pregnant and lactating women in the United States within the next 12 months."

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