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Mineral Iodine

Found in:

The iodine content of foods is dependent upon the iodine content in the environment in which they grew. The best sources of iodine are seafood and seaweed which are of limited significance in Western diets. Meat, milk and eggs may also provide iodine. The iodized salt, dried salted cod fish, cod liver oil, raw haddock, whole cow milk, human milk, whole milk yogurt, fruit.

What is known to be good for:

Iodine is required as a component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Thyroxine and triiodothyronine are required for normal energy metabolism, thermoregulation, intermediary metabolism, protein synthesis, reproduction, growth, physical and mental development, hematopoiesis and neuromuscular function.

Other functions of Iodine:

Iodine is essential for all animals, including humans.

Lack of Iodine:

It is the most common cause of endemic goiter and cretinism in the world. Endemic goiter is one of the most prevalent nutritional deficiency problems that afflicts millions of people in many parts of the world. Lack of iodine results in an enlargement of the thyroid gland (goiter). The enlargement is due to over stimulation of the thyroid by TRF and TSH which are present in increased levels in an attempt to produce more circulating T4 and T3. Severe iodine deficiency can produce myxedema which is characterized by a dry, waxy type swelling, with abnormal deposits of mucoproteins under the skin. Cretinism may occur when there is an insufficient supply of iodine to infants and young children resulting in lowered BMR, dwarfism and retarded mental development. The use of supplemental iodine such as iodized salt in areas where dietary iodine deficiency is endemic has dramatically reduced the incidence of cretinism in the world.

Excess of Iodine can:

Excessive dietary intake of iodine results in inhibition of thyroid hormone synthesis clinically known as the Wolff-Chaikoff effect. Generally, the body will adapt to the higher intake but in a few individuals the effect continues and the individual develops a goiter. Hyperthyroidism resulting from excessive iodine intake is characterized by increased basal metabolism, goiter and disturbances in the autonomic nervous systems causing hyperirritability and increased creatinine metabolism.

Do you know where you find Iodine in your body?

The adult human body contains 10-20 mg iodine, and about seventy to eighty percent of the iodine is concentrated in the thyroid gland. The remainder is distributed throughout the body with higher concentrations occurring in the salivary and gastric glands as well as in the dense connective tissue.

Storage and manipulation of suppliers of Iodine:

The metabolism of iodine occurs under hormonal feedback control. The uptake, synthesis and release of iodine by the thyroid gland is stimulated by thyroid stimulating hormone (TSH) released by the anterior pituitary gland. The release of TSH is dependent upon release of thyrotropin-releasing factor (TRF) from the hypothalamus. TRF release, in turn, is dependent upon levels of circulating T3 and T4. When circulating T3 and T4 levels are low, there is increased release of TRF.

Absorption, Storage and Excretion

Certain foods such as cabbage, rutabaga, and other members of the Brassica family contain goitrogens, which interfere with thyroid hormone synthesis. Under normal circumstances insufficient quantities of the goitrigen are ingested to be of clinical significance. Absorbed iodide is converted to iodine in the gut before it enters the circulatory system. Circulating iodine is taken up by the thyroid gland by an active transport process. The iodine is then oxidized and bound to the thyroid protein, thyroglobulin, and then may undergo oxidative coupling to form thyroxine (T4) and triiodothyronine (T3). T4 and T3 circulate in the bloodstream bound to thyroxine binding globulin, prealbumin and albumin. Excretion of iodine is largely via the urine. There is significant recycling of iodine derived from T4 and T3 metabolites from the tissues back to the circulation. T4 and T3 may be conjugated in the liver to glucuronate and sulfate with some losses via the bile although most of the T4 is reabsorbed.

Sources: Yeung, David L. and Idamarie Laquatra. HEINZ HANDBOOK Of Nutrition, 9th ed.

Adapted by Editorial Staff, July 2007
Last update, August 2008