Iodine in food and iodized salt is present in several chemical forms including sodium and potassium salts, inorganic iodine (I2), iodate, and iodide, the reduced form of iodine. Salt iodization programs, which many countries have implemented, have dramatically reduced the prevalence of iodine deficiency worldwide. In some regions of the world, iodine-deficient soils are common, increasing the risk of iodine deficiency among people who consume foods primarily from those areas. The earth’s soils contain varying amounts of iodine, which in turn affects the iodine content of crops. For example, it appears to play a role in immune response and might have a beneficial effect on mammary dysplasia and fibrocystic breast disease. Iodine may have other physiological functions in the body as well.
In the absence of sufficient iodine, TSH levels remain elevated, leading to goiter, an enlargement of the thyroid gland that reflects the body’s attempt to trap more iodine from the circulation and produce thyroid hormones. TSH secretion increases thyroidal uptake of iodine and stimulates the synthesis and release of T3 and T4. It is secreted by the pituitary gland to control thyroid hormone production and secretion, thereby protecting the body from hypothyroidism and hyperthyroidism. Thyroid function is primarily regulated by thyroid-stimulating hormone (TSH), also known as thyrotropin. They are also required for proper skeletal and central nervous system development in fetuses and infants. Thyroid hormones regulate many important biochemical reactions, including protein synthesis and enzymatic activity, and are critical determinants of metabolic activity. Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Iodine is a trace element that is naturally present in some foods, is added to some types of salt, and is available as a dietary supplement. For a reader-friendly overview of Iodine, see our consumer fact sheet on Iodine. This is a fact sheet intended for health professionals.
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