Iodine

Iodine (atomic weight 126.9045} is a relatively volatile halogen with valences I through 7. The term iodide refers to its ionic form 1-, iodate refers to lO3 Only isotope 127 occurs naturally, the radioactive isotopes 124. 125. 12S, 131. and 132 are produced artificially.

Abbreviations

Cys L-cysteine

TSH rhyroxine-srimulating hormone

Nutritional summary

Function: Iodine is an essential component of the thyroid hormones which have profound impact on development, growth, and metabolism.

Food sources: Good sources are lish, shellfish, seaweed, iodized salt, and fortified foods. Other foods provide variable amounts depending on the soil iodine content of their origin.

Requirements: Adults should get 150 jxg d: slightly more is needed during pregnancy and lactation.

Deficiency: A lack of iodine may cause spontaneous abortion and birth defects: it impairs irreversibly brain and physical development in the fetus and young child causing from mild to severe mental retardation, sometimes also hearing loss or paralysis of the legs. Deficiency in older children and adults stimulates excessive growth of the thyroid gland (goiter), slows metabolic rate, mental and cardiac function, and induces a feeling of fatigue and cold intolerance.

Excessive intake: Increased iodine intakes can promote thyroid hormone production in people with excessive function of the thyroid gland (autonomous hyperthyroidism). In healthy people, intakes above requirements (up to 2000|xg/d) will not confer any benefit, but appear to cause no harm. Chronic intake of several milligrams per day may disrupt thyroid function.

Dietary sources

Foods contain iodine mainly as iodide (I ). iodate (10; ), or thyroxine. Best iodine sources are marine fish, shellfish, seaweed, sea salt; iodized salt contains 76 jig iodideg, the iodide content of sea water is 50-60 ng/l (Hetzel el «/., 1990), Bread may contain iodate as a dough improver, and dairy foods may contain iodine from udder antiseptics. Urtsupplemcnted iodine content of foods closely correlates with the concentration in soil. Plants from iodine-sufficient soil contain around I ¡xg iodine/g dry weight. Plants from areas with iodine-depleted soils (old mountain ranges and coastal areas) contain only a fraction of that amount. Drinking water contains less than 2 p,g/| in iodine-deficient areas. Ty pical iodine intake m the US is 100 -150 fig/d.

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