Iodine

Other Name(s):

iodide, organic iodine, potassium iodide, sodium iodide

General Description:

In 1922, researchers discovered that the thyroid gland needs iodine to produce thyroid hormones and prevent the development of a goiter (enlarged thyroid). Thyroid hormones regulate metabolism, and affect reproductive processes, nerves, muscles, skin, and hair. In addition to preventing goiters, iodine helps with the synthesis of protein and utilization of oxygen.

Iodine is incorporated into two important hormones produced by the thyroid gland. Together, these two hormones regulate the metabolic rate of the body. They are extremely important in growth and development, particularly in the fetus and newborn, where deficiencies may result in mental retardation, abnormal appearance, and functional loss.

Medically Valid Uses:

Iodine is used to prevent and treat goiters, hyperthyroidism (over-active thyroid gland), iodine deficiency, and to prevent and/or treat thyrotoxic crisis. Goiters can be prevented by adding potassium iodide to table salt. Bread and water are alternative sources of iodine, if the iodine content is sufficiently high. Appropriate treatment of goiter during pregnancy is particularly critical for the health of the fetus.

Unsubstantiated Claims:

Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.

Iodine is claimed to reduce the risk of breast cancer, decrease fatigue, prevent weight gain, and treat arteriosclerosis (hardening of the arteries).

Recommended Intake:

Iodine supplements are essential for people living in the "goiter belt" (the Great Lakes states) or any other area lacking iodine in the soil. Adults who receive insufficient iodine in their diet can develop goiters (enlarged thyroid glands). If the lack of iodine is severe, they may also develop hypothyroidism (underactive thyroid gland). Mental retardation does not develop in adults who develop hypothyroidism.

It is estimated that before table salt was routinely supplemented with iodine, 50 to 70 percent of the people living in the Lake Michigan area had goiters. People who consume large amounts of "goitrogenic" vegetables such as cabbage, kale, Brussels sprouts, and rutabagas need additional iodine. Goitrogenic substances inhibit the absorption of iodine from the intestinal tract. Cooking deactivates goitrogenic substances.

Cretinism is a condition in which the thyroid gland did not function while the fetus was developing. This condition can lead to mental retardation and inhibit physical growth. Although cretinism is generally related to a congenital defect, it can be caused by profound iodine deficiency in the mother.

As indicated below, iodine is measured in micrograms. The RDA is the Recommended Dietary Allowance.

Group

RDA

Infant (0 to 6 months)

40 mcg

Infant (6 months to 1 year)

50 mcg

Children (1 to 3 years)

70 mcg

Children (4 to 6 years)

90 mcg

Children (7 to 10 years)

120 mcg

Men (11+ years)

150 mcg

Women (11+ years)

150 mcg

Pregnant women

175 mcg

Breast-feeding women

200 mcg

 

Food source

Nutrient content per 100 grams

Seaweed

61,990 mcg*

Iodized salt

10,000 mcg

Cod liver oil

838 mcg

Seafood, fish (depending on type of fish)

36-311 mcg

Seafood, shellfish (depending on type of shellfish)

31-129 mcg

Sea salt

94 mcg

* mcg = micrograms

Newborn infants who had insufficient iodine available while developing in the uterus are typically born with enlarged thyroids and evidence of hypothyroidism. Severe hypothyroidism can result in growth abnormalities and profound mental retardation.

Deficiencies in adults may result in a goiter (enlarged thyroid gland). An insufficient intake of iodine may result in hypothyroidism. Signs of hypothyroidism are slow mental reaction, dry skin and hair, loss of physical and mental vigor and alertness, and weight gain.

Side Effects, Toxicity and Interactions:

Elemental iodine, such as that found in "tincture of iodine" used to disinfect cuts, is extremely poisonous. Ingestion of even small amounts can be fatal.

Ingestion of potassium iodide or organically bound iodine preparations over a period of time, with doses approaching 1,000 micrograms/day can produce goiter and suppress the function of the thyroid. An excessive intake of iodine may cause a goiter similar to that seen with iodine deficiency. Excessive iodine may also depress the function of the thyroid, causing a mild hypothyroidism.

Women who are pregnant or breast-feeding should not take iodine supplements without consulting a physician. Excessive iodine intake may produce hypothyroidism in the newborn and the appearance of a goiter.

Since iodine interacts with lithium carbonate (taken for the manic phase of manic depressive syndromes), those taking lithium should avoid taking iodine supplements. Using iodine and lithium together may result in hypothyroidism. Also, avoid taking iodine supplements at the same time as taking amiodarone (a drug to control heart arrhythmias).

Additional Information:

Many areas of the country contain very little iodine in the soil. Subsequently, crops produced in these areas, and animals raised on these crops, contain very little iodine. Prior to the addition of iodine to table salt, these iodine-poor areas produced a large number of people with goiters (an enlargement of the thyroid gland caused by insufficient iodine in the diet). This problem has largely disappeared following the iodination of salt and the widespread consumption (even inland) of ocean fish and shellfish. However, despite iodized salt, daily iodine intake appears to be decreasing.

Iodized salt contains potassium iodide, usually in a ratio of one part iodine to 10,000-100,000 parts salt. Although this means there is actually very little iodine in salt, there is a sufficient amount to prevent the development of a goiter. Typically, iodized salt produced in the United States contains 76-100 micrograms of iodine per gram of salt.

Click here for a list of reputable Web sites with general information on nutrition.

References:

  1. Behrman RE, Kliegman RM, Nelson EE, Vaughan VC, eds. Nelson Textbook of Pediatrics. 14th ed. Philadelphia, PA: W.B. Saunders Co.; 1992.

  2. Braunwald E, Isselbacher KJ, Petersdorf RG, Wilson JD, Martin JB, Fauci AS, eds. Harrison's Principals of Internal Medicine. 11th ed. New York, NY: McGraw-Hill; 1987.

  3. Ingenbleek Y, Jung L, Ferard G, Bordet F, Goncalves AM, Dechoux L. Iodised rapeseed oil for eradication of severe endemic goitre. Lancet. 1997;350(9090):1542-5.

  4. Lee K, Bradley R, Dwyer J, Lee SL. Too much versus too little: the implications of current iodine intake in the United States. Nutr Rev. 1999;57(6):177-81.

  5. Smyth PP. The thyroid and breast cancer: a significant association? Ann Med. 1997;29(3):189-91.

  6. Smyth. PP, Delange F. The disorders induced by iodine deficiency. Thyroid. 1994;4(1):107-28.

  7. Hetzel BS. The Story of Iodine Deficiency: An International Challenge in Nutrition. Delhi: Oxford University Press; 1989.

  8. Stanbury JB, ed. The Damaged Brain of Iodine Deficiency. Elmsford, NY: Cognitive Communications Corp.; 1994.

  9. Smolin LA, Grosvenor MB. Nutrition Science and Applications. 2nd ed. Sanders College Publishing; 1997.

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