Iodine is a mineral that plays a key role in the metabolism (process of converting food to energy) of cells. It is part of the thyroid hormones thyroxin and triiodothyronine, which perform various roles in the body.

Most Americans obtain their iodine through the use of iodized table salt. This is salt that has been fortified with iodine. Milk and breads are also good sources of iodine. Salt water in the ocean is the major source of the world’s iodine. Iodine is found in salt water, seafood (e.g., cod, sea bass, haddock and perch) and plants that grow near salt water, including kelp (seaweed).

A lack of iodine typically is not a problem for Americans, but more than 1 billion people worldwide suffer from this type of deficiency, according to the Thyroid Foundation of America.

Iodine deficiency is the leading cause of preventable mental deficiency in the world. A moderate deficiency of iodine can lead to a swelling of the thyroid gland (goiter). More severe deficiencies of iodine in a pregnant woman can lead to a severe form of mental and physical retardation (cretinism) in her child. Excessive levels of iodine can also cause health problems, including goiter.