Physiology Dietary Sources and Requirements

R Houston, Emory University, Atlanta, GA, USA © 2005 Elsevier Ltd. All rights reserved.

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Iodine is classified as a nonmetallic solid in the halogen family of the Periodic Table of the elements and therefore is related to fluorine, chlorine, and bromine. The halogen family lies between the oxygen family and the rare gases. Iodine sublimates at room temperature to form a violet gas; its name is derived from the Greek iodes, meaning 'violet-colored.' Iodine was discovered by Bernard Courtois in Paris in 1811, the second halogen (after chlorine) to be discovered. It took nearly 100 years to understand its critical importance in human physiology. In 1896, Baumann determined the association of iodine with the thyroid gland, and in 1914 Kendall, with revisions by Harrington in 1926, described the

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hormone complexes synthesized by the thyroid gland using iodine that are so integral to human growth and development.

As the biochemistry of iodine and the thyroid was being established, the scarcity of the element in the natural environment became evident and the link between deficiency and human disease was revealed. Enlargement of the thyroid, or goitre, is seen in ancient stone carvings and Renaissance paintings, but it was not until years later that the link with lack of iodine was firmly established. Even with this knowledge, many years passed before preventive measures were established. From 1910 to 1920 in Switzerland and the USA work was done on the use of salt fortified with iodine to eliminate iodine deficiency, with classic work being done by Dr David Marine in Michigan. Recently the linkage of iodine deficiency with intellectual impairment has brought iodine into the international spotlight.

Recent work has demonstrated that the halogens, including iodine, are involved through the halo-peroxidases in enzymatic activity and production of numerous active metabolites in the human body. While the importance of iodine for the

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