Kashin-Beck disease--expanding the spectrum of iodine-deficiency disorders.

Selenium, as selenocysteine, is an integral component of two important enzymes — glutathione peroxidase and iodothyronine deiodinase — that are present in many tissues, including the thyroid gland. Glutathione peroxidase catalyzes the breakdown of hydrogen peroxide, thereby protecting against oxidative damage. Iodothyronine deiodinase catalyzes the deiodination of thyroxine to triiodothyronine, a more potent thyroid hormone. Iodine is not an integral component of any enzyme, but it is an integral component of thyroxine and triiodothyronine. Selenium and iodine are thus linked biochemically because both are involved in thyroid hormone production.