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More on Iodine

I am listening to an excellent talk by Stefan Hartmann (PA-C) on iodine. Hopefully he will grace us with this talk in the near future.

While listening I sought to find out why selenium is an important cofactor to iodine. This research paper provides an excellent summary:

Role of Iodine, Selenium and Other Micronutrients in Thyroid Function

and Disorders


Key Highlights:

  • It is remarkable that the production as well as the metabolism of thyroid hormone are dependent on two trace elements: iodine and selenium.

  • The thyroid gland requires iodine for the synthesis of thyroid hormones: thyroxine (3,5, 3’,5’-tetraiodothyronine or T4) and triiodothyronine (3,5,3’- triiodothyronine or T3).

  • T3, the physiologically active thyroid hormone, is produced either directly by the thyroid and by means of conversion catalyzed by selenium-containing deiodinases from the circulating T4 in peripheral tissues. It can bind to specific receptors in the nuclei of cells and regulate gene expression particularly in the liver, pituitary, muscle, and brain.

  • In this way, thyroid hormones regulate a number of physiologic processes, including growth, development, metabolism, and reproductive function [1, 2].

  • Three different selenium-dependent iodothyronine deiodinases (types I, II, and III) can both activate and inactivate thyroid hormones, making selenium an essential micronutrient for normal development, growth, and metabolism. Furthermore, selenium is found as selenocysteine in the catalytic center of enzymes protecting the thyroid from free radicals damage. In this way, selenium deficiency can exacerbate the effects of iodine deficiency and the same is true for vitamin A or iron deficiency.

  • Selenium-containing enzymes (GPx, PHGPx) participate in the protection of thyroid cells against H2O2 and free radicals. The H2O2 exposure is greatest when TSH levels are higher, as is the case of iodine deficiency. Thus, iodine deficiency increases H2O2 generation, whereas Se deficiency, impairing the enzyme activity, decreases its disposal.

  • Iodine Excess It is rare for diets of natural foods to supply iodine in excess. People living in the northern coastal regions of Japan have been found to have iodine intakes ranging from 50,000 to 80,000 mcg (50-80 mg) of iodine/day due a large amounts of seaweed in the diet [1].

  • Most people can be exposed to large amounts of iodine without apparent problems [106].


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