Iodine: Iodine is a trace mineral produced by the body that is essential for normal growth and development. Seventy to eighty percent of iodine is found in the thyroid gland in the neck. The rest is distributed throughout the body, particularly in the ovaries, muscles, and blood. A deficiency of iodine can lead to hypothyroidism; symptoms of this condition include sluggishness, weight gain, and sensitivity to temperature changes. In infants and children, hypothyroidism can impair physical and mental development.

The classic sign of iodine deficiency is an enlarged thyroid gland. Some people with hypothyroidism develop an extremely large thyroid, known as goiter. Today, iodine deficiencies in the United States and other developed countries are rare because table salt is supplemented with iodine and crops in developed countries are generally grown in iodine-rich soil. In developing countries, however, where soil is often low in iodine, more than one billion people are estimated to be at risk for disorders caused by iodine deficiencies.