What is Wolff Chaikoff effect ?

Wolff-Chaikoff effect:

Iodine deficiency leads to severe mental deterioration especially in children. The recommended dietary intake of iodine is 150µg/day for adults but increases during pregnancy and lactation. If iodine intake drops below 50µg/day then hypothyroidism results. High iodine intake (e.g. in amiodarone therapy) can induce hypothyroidism, goiter and sometimes hyperthyroidism. A large excess of iodide, when given acutely, inhibits the adenylate cyclase response to TSH and iodination of thyroglobulin also inhibit thyroglobulin hydrolysis. This is termed the Wolff-Chaikoff effect.

After few day of exposure to high iodide concentration, thyroidal uptake is very low, the intrathyroidal iodide concentration falls and the synthesis of iodinated Tg recommences. This effect can be used to prepare a thyrotoxic patient for thyroidectomy by giving excess KI.