Iodine is a trace element that plays a significant role in the healthy functioning of the thyroid. Humans typically contain about 20 to 30 milligrams of iodine. While this element is present in the muscles, skin, bones, and blood, it lies primarily in the thyroid. Iodine is essential to thyroid hormone production, which helps regulate various processes in the body, including physical and mental development and metabolism.

Sources of Iodine

Unlike other minerals, the body does not hold onto iodine; rather, it is filtered by the kidneys and flushed rather quickly from the body through urine. In turn, since the body consistently uses and flushes iodine, it is important that people consistently ingest iodine in order to maintain appropriate levels. Oceanic food sources are an excellent natural source of iodine: fish and shellfish, including cod, sea bass, and perch, are good sources of iodine, as is seaweed.

The levels of iodine found in other foods, such as meats, eggs, dairy products, and vegetables, vary depending on the conditions in which these food sources are raised or grown. Meats may be rich in iodine if the animals from which the meats come consume an iodine-rich diet; similarly, vegetables that are grown in iodine-rich soil have higher levels of iodine. Soil closer to the coast is usually richer in iodine, and in turn, the food harvested from this soil typically has higher iodine content. Specific foods that are usually good sources of iodine, especially when grown in iodine-rich soil, include pineapple, cantaloupe, lettuce, spinach, and mushrooms.

Iodized salt is typically the main source of iodine for most people; there are about 70 micrograms of iodine in one gram of salt. In turn, a person would only need to ingest about two to three grams of iodized salt daily to meet the recommended intake of about 150 micrograms of iodine. While sea salt is a natural source of iodine, it does not contain as much iodine as iodized salt. Iodine supplements in tablet or liquid form are also available.

Functions of Iodine

The thyroid holds the greatest concentration of iodine in the body. Iodine is used primarily in the production of thyroid hormones, particularly thyroxine and triiodothyronine, and therefore is a significant factor in the proper functioning of the thyroid gland. The thyroid gland is responsible for how the body uses energy, for setting the basal metabolic rate (BMR); it influences physical and mental development, the functioning of the nervous system, and metabolism. The thyroid also plays a role in protein and cholesterol synthesis, as well as the absorption of carbohydrates. Since the thyroid regulates how the body uses energy, it also has an effect on many of the bodily processes and functioning in general. It can have a significant effect on reproduction as well as nerve and bone development, among other things.

Uses of Iodine

Iodine is primarily used to prevent and treat conditions that occur from an iodine deficiency. Iodine may be used to treat goiter and hypothyroidism, conditions that typically occur due to insufficient iodine levels. In helping to insure that the thyroid functions properly, iodine may also decrease the risk of atherosclerosis because the thyroid helps regulate how the body metabolizes fat and cholesterol. Iodine also helps treat fibrocystic breast disease because people suffering from this disease often demonstrate low levels of the mineral. Iodine supplementation may also help prevent miscarriages caused by low levels of iodine, and may protect against thyroid damage and thyroid cancer by preventing the thyroid from using radioactive iodine instead of regular iodine. Iodine has also been shown to keep skin, nails, and hair healthy, and iodine solutions are frequently used as antibacterial agents.

Iodine Deficiency

Goiter and hypothyroidism are perhaps the most common and well known results of iodine deficiency. When a person does not maintain sufficient levels of iodine, the cells of the thyroid gland expand in an attempt to catch more iodine; a goiter is when the entire gland becomes enlarged. Symptoms of hypothyroidism, a condition in which the thyroid does not function properly, include fatigue, weight gain, and decreased mental functioning. Cretinism is a condition that affects babies and children who have not received sufficient amounts of iodine; this condition results in mental impairment and other problems. Iodine deficiencies have also been linked to increased risk of some cancers, especially breast cancer.

People living in certain areas of the world are more prone to iodine deficiencies, primarily due to the lack of iodine available in the soil of these regions. Because there is little iodine in the soil, and therefore little iodine in the food, it is more difficult for people to meet the daily iodine recommendations. Such regions include Switzerland, Central America, mountainous regions of South America, New Zealand, and the Himalayas. In the United States, people who live near the Great Lakes, in the Midwest, and in the Pacific Northwest are more prone to iodine deficiencies; in fact, such deficiencies were what prompted iodine to be added to table salt in the 1920s. The introduction of iodized table salt significantly decreased the incidence of iodine deficiency. Women in general seem to be more likely to experience iodine deficiencies, especially adolescent, pregnant, and menopausal women.

Certain foods may contribute to iodine deficiencies. Foods including cabbage, soybeans, and peanuts, among others, include goitrogens; goitrogens prevent the body from properly using iodine, and therefore can contribute to iodine deficiency. However, cooking these foods lessens or eliminates the negative effects of these substances.

Up to 1,000 micrograms of iodine can be tolerated within the body; however, extended elevated levels of iodine can lead to iodine toxicity. Symptoms of iodine toxicity include headache, rash, difficulty breathing, and a metallic taste in the mouth.         

Required Daily Amount

All men and women are recommended to intake about 150 micrograms of iodine daily. For people who live in areas in which iodine levels in the soil are low, and therefore who are at risk of iodine deficiency, the recommendation increases to 150 to 300 micrograms of iodine.


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