Iodine, a halogen element, has importance in human health as a component of the hormone thyroxine (produced by the human thyroid gland). Thyroxine is an important part of general metabolism regulation and normal fetal development.

Iodine deficiency can lead to an enlargement of the thyroid gland (e.g. goiter) and other related disorders. Severe maternal iodine deficiency during pregnancy can lead to fetal cretinism, a form of mental retardation. Less severe deficiencies during pregnancy can lead to lesser degrees of neurological damage, which generally manifest as poor cognitive performance and hearing impairment. These conditions are rare in the U.S. as iodine is easily accessible, especially from iodized salt.

Food sources of iodine include milk, bread, fish, various fruits and vegetables, and legumes.