Iodine: What you see is often not what you get

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Iodine is crucial to the development of fetuses and infants and mothers-to-be often take supplements containing the element to ensure that they are getting enough. But a new study shows that many supplements -- particularly those in which the iodine is derived from kelp -- do not contain as much as they claim.

Severe iodine deficiency can cause cretinism, which is marked by severely stunted physical and mental development, but even a mild deficiency can cause neurological impairment. The widespread use of iodized table salt had reduced this problem in developed countries, but growing restrictions on salt use for health reasons have caused it to reappear. Recent national surveys of women of child-bearing age show that more than a third have at least a mild iodine deficiency.

Dr. Elizabeth Pearce and her colleagues at Boston University School of Medicine identified 114 non-prescription and 27 prescription multivitamins containing iodine and randomly tested 60 of them. They reported Wednesday in the New England Journal of Medicine that the supplements in which the iodine came from potassium iodide contained an average of about 75% of the amount claimed on the label.

But those in which the iodine came from kelp -- which is known to have variable concentrations of the element -- were all over the place, ranging from a low of about 22% of the claimed value to a high of 300%. Pearce recommended that women use only multivitamins in which iodine is provided in the form of potassium iodide and that all manufacturers use only potassium iodide at a dose about 30% higher than the label claims.

-- Thomas H. Maugh II