Iodine is a nonmetallic mineral essential in human nutrition. The highest concentrations of iodine in the human body are found in the thyroid gland, muscles, and endocrine tissues. Iodine functions as a primary component of thyroxin and triiodotyrosine, thyroid hormones that regulate growth, development, energy metabolism, and body temperature. Supplemental forms of iodine include inorganic iodides (iodine bonded to sodium or potassium) and organic sources such as kelp and iodine casseinate.
Iodine is found primarily in seafoods, including seaweed. It can also be found in foods grown on iodine-rich soil. In most developed countries, the primary source of dietary iodine is iodized salt, which generally provides 70 micrograms of iodine per gram of salt.
The Reference Daily Intake (RDI) for iodine is 150 micrograms per day. With the prevalence of iodized salt, most people can easily get this amount in their regular diet. Iodine toxicity is rare, seen primarily in people consuming large quantities of seaweed and in those with excessive exposure to iodine-containing chemicals. Excessive iodine intake has been associated with inflammation of the thyroid, thyroid enlargement, abnormal heart beat, heart failure, and an increased risk for Graves' disease.