Iodine or Iodide? A Laboratory Evaluation of the Content of Powdered Iodine Supplements

Background: Iodine is a vital micronutrient essential for thyroid hormone synthesis and neurological development in utero and in the early postpartum period. Maternal iodine deficiency during pregnancy can result in infant congenital hypothyroidism. Congenital hypothyroidism is the most prevalent preventable cause of mental retardation in the world. Some proponents of supplementation believe that products containing both iodine (I2) and iodide (I−) are therapeutically superior to iodide-only formulations. As a step toward evaluating this claim, we tested three commercially available products that list both iodine and iodide on the label, to determine their content.Design: Two powdered and one aqueous solution were tested using ion chromatography, X-ray spectrometry, ion coupled mass spectrometry, and the iodine-starch test to more accurately determine their composition.Results: We found that when each of the dry supplements were dissolved in a slightly basic solution, only the I− form was then present.Conclusion: Our findings suggest that dry products made with only iodide are likely to be substantially equivalent to dry products made with both forms, at least by the time they are digested and absorbed.