WEDNESDAY, Feb. 25 (HealthDay News) -- Most prenatal vitamins marketed in the United States don't contain as much iodine as is stated on the label, researchers report.
The variance is troubling, they say, since iodine is critically important to the health of a developing fetus.
In a letter appearing in the Feb. 26 issue of the New England Journal of Medicine, the team also noted that the actual levels of iodine found in the supplements were typically below those recommended by the American Thyroid Association (ATA).
"Iodine nutrition is critically important in pregnancy," explained Dr. Elizabeth Pearce, co-author of the letter and an assistant professor of medicine at Boston University Medical Center. "Women who are deficient in pregnancy have children often with lower IQs or neurocognitive delays. Iodine deficiency is the leading cause of preventable mental retardation in the world."
But, based on the new findings, "it seems that an ideal prenatal vitamin, in terms of iodine, does not exist," she said. "About half of them have iodine that's derived from kelp and that's very variable."
Through an Internet search, the authors found 127 nonprescription and 96 prescription prenatal vitamins currently available in the United States.
Product labeling on 114 products (87 nonprescription and 27 prescription) claimed that the vitamins contained iodine. According to the labeling, 101 (89 percent) of these products contained at least 150 micrograms of iodine in a daily dose.
Sixty-seven vitamins contained iodine from potassium iodide, 42 from kelp, and five from some other source.
"Products containing iodine from potassium iodide tended to be more consistent, [but] 150 micrograms of potassium iodide is not the same as 150 micrograms of iodine," Pearce stressed. "If you really want people to get what the American Thyroid Association [ATA] has recommended -- which is 150 micrograms [of iodine] a day in a supplement -- there isn't one, but we would prefer products made from potassium iodide."
After measuring actual iodine contained in 60 randomly selected products, the authors determined that the mean dose overall was 119 micrograms of iodine. But this level varied widely, depending on where the iodine came from. For example, potassium iodide contained about 76 percent iodine, while the level of iodine from vitamins with kelp ranged anywhere from 33 to 610 micrograms per daily dose.
In 13 of the vitamin brands sampled, the actual iodine content differed from what was stated on the labeling by 50 percent or more, the researchers reported.
"The values of iodine are all over the map," Pearce concluded.
Beyond being essential for the developing fetus, iodine is also critical for women who are breast-feeding. And adults who don't have enough of the element can develop goiter.
According to background information in the article, 2.2 billion people worldwide suffer from iodine deficiency.
The ATA recommends that women who are pregnant or breast-feeding take prenatal vitamins with 150 micrograms of iodine a day. Both the Institute of Medicine (IOM) and the World Health Organization (WHO) recommend higher amounts. The IOM suggests 220 micrograms daily during pregnancy and 290 micrograms while breast-feeding; the WHO recommends 250 micrograms daily during both pregnancy and breast-feeding.
According to the researchers, manufacturers should only use potassium iodide and should make sure supplements contain at least 197 micrograms of potassium iodide to ensure the recommended dose of iodine.
A representative of the supplements industry welcomed the findings.
"We compliment the article for identifying a significant potential problem and recommending to some degree that something be done about it," said John Hathcock, senior vice president for scientific and international affairs at the Council for Responsible Nutrition, in Washington, D.C. "If iodine levels keep declining [iodine levels in U.S. adults have decreased by about 50 percent since the 1970s, most dramatically among women of childbearing age] and maybe even at present levels, there could be pockets of individuals with certain dietary habits who could [develop problems]."
Differences in labeling requirements for drug or food products on the part of the U.S. Food and Drug Administration may also account for some of the discrepancies, Hathcock added.
The good news, Pearce said, is that mild iodine deficiency in the United States is not likely to result in major or even detectable neurodevelopmental delays.
"But because we know the potential is there and it's such an easy thing to prevent, it makes sense to make sure that women get adequate iodine nutrition," she said.
Consumers should be able to read on the label whether the iodine comes from kelp or potassium iodide, she said.
There's more on iodine deficiency at the American Thyroid Association.
SOURCES: Elizabeth N. Pearce, M.D., assistant professor, medicine, Boston University Medical Center; John Hathcock, Ph.D., vice president, scientific and regulatory affairs, Council for Responsible Nutrition, Washington, D.C.; Feb 26, 2009, New England Journal of Medicine