Wolff–Chaikoff effect

[woo͡lf′ chī′kəf]
the decreased formation and release of thyroid hormone in the presence of an excess of iodine.

The Wolff–Chaikoff effect is hypothyroidism caused by ingestion of a large amount of iodine. Whether or not daily ingestion of 1000 mcg - 12.5mg (mixed iodide/iodine) doses by otherwise healthy adults will cause this effect in a statistically significant number of patients has not yet been proven in human studies.
It is an autoregulatory phenomenon which inhibits formation of thyroid hormones inside of the thyroid follicle. This becomes evident secondary to elevated levels of circulating iodide. The Wolff-Chaikoff effect lasts several days (around 10 days), after which it is followed by an "escape phenomenon", which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" is believed to occur because of decreased inorganic iodine concentration secondary to down-regulation of sodium-iodide symporter on the basolateral membrane of the thyroid follicular cell.
The Wolff–Chaikoff effect can be used as a treatment principle against hyperthyroidism by infusion of a large amount of iodine to shut down the hyperfunctioning thyroid gland, or an unpleasant iatrogenic effect of several iodine containing drugs, of which the most famous is amiodarone.
The Jod-Basedow phenomenon is iodine-induced hyperthyroidism.

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