Biochemical and physiological roles
This trace mineral is used for the production of thyroid hormones , including triiodothyronine (T3) and thyroxine (T4). It is absorbed and transported to the thyroid in the iodide form. Then oxidized by thyroid peroxidases to iodize tyrosine residues and lead to tetraiodothyronine or thyroxine (T4). Thyroxine is partially deiodinated at T3 by liodothyronine 5'deiodase, a seleno-dependent enzyme. T3 is the most active hormonal form. A deficit induces a decrease in the level of thyroid hormone with the triggering of regulations by the hypothalamic-pituitary axis: hypothalamic "Thyrotropin Releasing Hormone" (TRH) and TSH, pituitary thyroid-stimulating hormone. With this deficit, the hyperstimulation of the thyroid causes the gland to hypertrophy: this is goiter.
Iodine needs and recommended intakes
The main sources are fish , shellfish , dairy products and eggs . In most countries the needs are not covered if the salt is not iodized. Recent work (LAMAND and TRESSOL, 1992) indicates that, to cover the needs , all salts (household and industrial) should be iodized at 20 mg/kg to compensate for losses during salt storage (coarse salts or fine salts) even stored in good conditions. The intakes recommended by most authors are 150 µg/day .