Iodine

Iodine is needed to synthesize a key hormone of the thyroid gland, thyroxine, which is involved in regulating metabolic rate, growth, and development. An iodine deficiency leads to goiter, a swelling of the thyroid gland in the front of the neck. Goiter was once common in the United States, but the use of iodized salt has eliminated the condition in this country. An excessive intake of iodine depresses thyroid activity, so taking supplemental doses of iodine is not recommended.