Читать книгу Anti-Aging Therapeutics Volume XIV - A4M American Academy - Страница 55

Biochemically, iodine’s main function is as an essential component of thyroid hormones. Thyroxine (T4) and triiodothyronine (T3) are comprised of approximately 65 and 59% iodine by weight, respectively.⁷ All mammals depend on thyroid hormones for regulation of enzymatic activity and protein synthesis. Once ingested, iodine is converted into elemental iodide, and taken up by the thyroid gland via the activity of a sodium-iodide symporter pump. This pump allows the thyroid to concentrate iodine by 20 to 50-fold above serum levels. The kidneys excrete 90% of iodine left in circulation with variable amounts eliminated via feces and sweat. Iodine is present in concentrated amounts in the salivary glands, breast tissue, the gastric mucosa, and the choroid plexus. With the exception of iodine concentrated via lactating breast tissue, the physiological significance of iodine at the other sites is not yet known.⁸

In times of iodine excess, the sodium-iodide transport pumps decrease in activity. When iodine excess is severe or persistent, there is inhibition of thyroid hormone production within the gland. This effect is called the Wolff-Chaikoff effect, and is named after the first researchers to observe it in an animal model. The possible mechanisms for this reduction include an inhibition of thyroxin secretion, inhibition of oxidization of iodine within the thyroid, and inhibition of the iodination of tyrosine within the thyroid follicles. The Wolff-Chaikoff effect usually reverses in 2-3 weeks after withdrawal of the excess iodine. This effect has been utilized therapeutically to suppress hyperthyroid states, mostly prior to the advent of thioamide thyrotoxic drugs.⁹

In a slightly deficient iodine state, the thyroid gland swells to compensate, often leading to goiter. Also counter logical is the fact that in the face of iodine excess, the thyroid commonly ends up being slowed into a hypothyroid state.