Iodine is a trace mineral and an essential nutrient found naturally in the body.

Iodine is needed for the normal metabolism of cells. Metabolism is the process of converting food into energy. Humans need iodine for normal thyroid function, and for the production of thyroid hormones.

Iodized salt -- table salt with iodine added -- is the main food source of iodine. Seafood is naturally rich in iodine. Cod, sea bass, haddock, and perch are good sources. Kelp is the most common vegetable seafood that is a rich source of iodine. Dairy products also contain iodine. Other good sources are plants grown in iodine-rich soil.

Lack of enough iodine (deficiency) may occur in places that have iodine-poor soil. Many months of iodine deficiency in a person's diet may cause goiter or hypothyroidism. Without enough iodine, the thyroid cells and the thyroid gland become enlarged.

Deficiency happens more often in women than in men, and is more common in pregnant women and older children. Getting enough iodine in the diet may prevent a form of physical and mental retardation called cretinism. Cretinism is very rare in the U.S. because iodine deficiency is generally not a problem.

Iodine poisoning is rare in the U.S. Very high intake of iodine can reduce the function of the thyroid gland.

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.

A 1/4 teaspoon of iodized table salt provides 95 micrograms of iodine. A 6-ounce portion of ocean fish provides 650 micrograms of iodine. Most people are able to meet the daily recommendations by eating seafood, iodized salt, and plants grown in iodine-rich soil. When buying salt make sure it is labeled "iodized."

The Food and Nutrition Board at the Institute of Medicine recommends the following dietary intake for iodine:

Infants

• 0 - 6 months: 110 micrograms per day (mcg/day)
• 7 - 12 months: 130 mcg/day

Children

• 1 - 3 years: 90 mcg/day
• 4 - 8 years: 90 mcg/day
• 9 - 13 years: 120 mcg/day

Adolescents and Adults

• Males age 14 and older: 150 mcg/day
• Females age 14 and older: 150 mcg/day

Specific recommendations depend on age, gender, and other factors (such as pregnancy). Women who are pregnant or producing breast milk (lactating) need higher amounts. Ask your health care provider which amount is best for you.

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Mason, MB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 237.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine,Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington, DC, 2001.