Iodine

Most of the iodine in the body occurs in the thyroid gland. Iodine in the thyroid gland is necessary for the formation of thyroid hormones.

Iodine Deficiency

Iodine deficiency is rare, because in most countries, iodine (as iodide) is added to commercial table salt.

When iodine is deficient, the thyroid gland enlarges, forming a goiter, as it attempts to capture more iodine for the production of thyroid hormones. Iodine deficiency causes the same symptoms as an underactive thyroid gland (hypothyroidism (see Section 13, Chapter 163)). In adults, such symptoms include puffy skin, a hoarse voice, impaired mental function, dry and scaly skin, sparse and coarse hair, and weight gain. If a pregnant woman has this deficiency, the growth and brain development of the fetus may be abnormal. Unless the baby is treated soon after birth, mental retardation with short stature (cretinism) develops. If a nuclear radiation accident occurs, iodine deficiency increases the risk of thyroid cancer in children because the deficient thyroid gland collects the radioactive iodine.

The diagnosis of iodine deficiency is based on blood tests indicating low levels of iodine and thyroid hormones or a high level of thyroid-stimulating hormone (TSH) or on the presence of a goiter (only in adults). Treatment consists of iodine supplements. Infants may also require supplements of thyroid hormone, sometimes throughout life.

Iodine Excess

Excess consumption of iodine is uncommon. It usually results from taking iodine supplements to treat a prolonged iodine deficiency. Sometimes people who live near the sea consume too much iodine because they eat a lot of seafood and drink water that is high in iodine. Iodine excess may cause the thyroid gland to become overactive and produce excess thyroid hormones (a disorder called hyperthyroidism (see Section 13, Chapter 163)). As a result, the thyroid gland enlarges, forming a goiter.

The diagnosis is based on symptoms and on high levels of iodine and thyroid hormones and a low level of thyroid-stimulating hormone (TSH) in the blood. Treatment involves using salt that is not fortified with iodine and reducing consumption of foods that contain iodine.