Iodine

Iodine, the form in which iodine is found in food, is required in extremely small amounts for normal thyroid gland functioning. Once in the body, iodine is chemically changed to iodide. The thyroid gland, located in the neck, is responsible for producing two important hormones that maintain a normal level of metabolism and are essential for normal growth and development, body temperature, protein synthesis, and much more. Iodide is a part of both these hormones.

• Thyroid gland—A gland found on either side of the trachea that produces and secretes two important hormones that regulate the level of metabolism.

Iodine is not found in many foods: mostly saltwater fish and grains grown in iodine-rich soil (once covered by the oceans, soil in the central states contains little iodine). Iodized salt was introduced in 1924 to combat iodine deficiencies. Iodine also finds its way accidentally into milk (cows receive iodine-containing drugs, and dairy equipment is sterilized with iodine-containing compounds), and into baked goods through iodine salts used as dough conditioners. Processed foods in the United States do not use iodized salt.

Average intake in the U.S. is more than recommended but less than toxic. A deficiency can cause hypothyroidism, a condition in which less thyroid hormone is made, leading to low metabolic rate, tendency to weight gain, and drowsiness. A deficiency can also cause simple goiter, in which the thyroid gland becomes very large and the affected person feels lethargic, gains weight, and has a decreased body temperature. If a woman has an iodine deficiency during pregnancy (and possibly also a selenium deficiency), the development of the fetus will be harmed, and it could cause cretinism, a condition of mental and physical retardation.

• Hypothyroidism— A condition in which there is less production of thyroid hormones; this leads to symptoms such as low metabolic rate, fatigue, and weight gain.
• Simple goiter— Thyroid enlargement caused by inadequate dietary intake of iodine.
• Cretinism (congenital hypothyroidism)— Lack of thyroid secretion; causes mental and physical retardation during fetal and later development.