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Iodine: Health Benefits, Deficiency and Goiter

Iodine is a trace mineral that is part of thyroid hormones, which help regulate the rate at which the body uses energy. Therefore, this mineral is essential to metabolism.

Iodized table salt is the main source of dietary iodine. Most people actually consume more iodine than is suggested, though iodine toxicity rarely occurs. Consuming more than 1,000 micrograms (1 milligram) of iodine per day can be dangerous, especially to the fetuses of pregnant women.

Recommended dietary allowances (RDAs) and tolerable upper intake levels of iodine expressed in micrograms (not milligrams) are as follows:

Age (both genders) RDA (mcg) Upper Limit (mcg)
Birth to 6 months 110 None established
7-12 months 130 None established
1-3 years 90 200
4-8 years 90 300
9-13 years 120 600
14-18 years 150, pregnant women 220, lactating 290 900
19 years and older 150, pregnant women 220, lactating 290 1,100

Health Effects of Iodine

Iodine, after being converted to iodide in the gastrointestinal tract, becomes part of the thyroid hormones thyroxin and triiodothyronine. These hormones regulate cell activity by controlling the rate at which cells use oxygen and thus influence the amount of energy released during basal metabolism. They are also vital to protein synthesis, blood cell production, tissue growth, nerve and muscle function, and reproduction.

In medicine, iodine is used as a topical disinfectant to kill bacteria and prevent infections in minor scrapes and cuts. In oral form, iodine may be used to treat overactive thyroid (hyperthyroidism) and iodine deficiency. In addition, radioactive iodine is used to treat hyperthyroidism and thyroid cancer.

Iodine Deficiency

Deficiency of iodine, though not a problem in the Western world, is the leading cause of preventable mental deficiency in the third world countries. It tends to affect women more than men, especially pregnant women as well as older children.

However, patients with elevated blood pressure, diabetes or kidney problems who drastically cut back their sodium intake put themselves at increased risk of iodine deficiency. Iodine deficiency can cause a drop in the production of thyroid hormones. As a result, the body begins to burn energy more slowly, leading to weight gain. In addition, a drop in thyroid hormone levels causes the cells of the thyroid gland to swell in an attempt to take in as much iodide as possible. This may lead to a visible lump in the neck, a condition known as goiter.

Children who have even a mild deficiency of iodine may experience goiters. Mental problems and learning difficulties may result. Fortunately, this condition is usually reversible with treatment. However, pregnant women with severe iodine deficiency may give birth to babies with extreme, irreversible mental and physical retardation known as cretinism. Symptoms include deafness, dwarfism, mutism, spasticity and other neuromuscular abnormalities.

Other medical conditions associated with a deficiency of iodine include:

  • Hypothyroidism or underactive thyroid (insufficient production of thyroid hormones)
  • Impaired growth
  • Increased infant mortality and stillbirths
  • Infertility
  • Miscarriages and other pregnancy complications

Eating too much of foods that contain the antithyroid substance goitrogen can also lead to goiter, because dietary iodine cannot counteract the effect of this substance. Foods particularly rich in goitrogen include cruciferous vegetables like bok choi, broccoli, Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, mustard, radishes, rutabagas, and turnips. Other foods high in goitrogen are bamboo shoots, peaches, peanuts, pears, soy products, spinach, strawberries, sweet potatoes and wheat.

Iodine Overdose

In fact, excessive consumption of iodine can also cause goiter as the thyroid gland accelerates its production of thyroid hormone. For example, people who eat large amounts of dried seaweed over a long period of time are at risk of developing this type of goiter.

Confusion and irregular heartbeat are other symptoms associated with an overabundance of iodine. Pregnant women, in particular, should avoid foods, drugs and prenatal supplements that can cause iodine overdose. Fetuses exposed to toxic amounts of iodine may develop large goiters that block their airways and cause suffocation.

Dietary Sources of Iodine

Iodized salt is the major source of dietary iodine for most people. Even small amounts of table salt fortified with iodine provide enough of this mineral to meet a person’s daily requirements. Other good sources include seafood (e.g., cod, haddock, perch and sea bass), certain plants that grow near the ocean such as seaweed (kelp), milk, bread and vegetables or other plants grown in iodine-rich soil.

Where to Get More Information: American Thyroid Association