Iodine Deficiency Disorders

Iodine, a nonmetallic solid in the halogen family, is an essential constituent of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Thyroid hormones are involved in a wide range of biological functions and modulate gene expression through specific nuclear receptors. Iodine is present in small amounts in soil, water, plants, and animals, and insufficient dietary intake of iodine is generally related to lack of iodine in the soil. The iodine-deficiency disorders consist of a wide spectrum of disorders including mental retardation, impaired physical development, increased perinatal and infant mortality, hypothyroidism, cretinism, and goiter. Goiter is defined as an enlargement of the thyroid gland, and cretinism is a term used for a severe form of iodine deficiency characterized by severe mental retardation. The effects of iodine deficiency are most pronounced during periods of rapid growth, that is, in the fetus, neonate, infant, and young children, and this may have a major effect on brain development. The ongoing global effort to eliminate iodine-deficiency disorders through iodization of salt represents one of the largest public health efforts of the 20th century.