Iodine

Iodine has one recognized role in human health, and that is in the formation of thyroxin, the thyroid hormone. Thyroxin regulates the metabolic rate of the body, and the availability of iodine affects the amount of hormone secreted. When there is a deficiency of iodine, the thyroid attempts to compensate by secreting more thyroxin. The gland then becomes enlarged, swollen, and congested. This is known as goiter. If insufficient iodine is present in a developing fetus, physical and mental retardation-cretinism-can result.

Goiter and cretinism are known to occur in areas of the world where iodine is low or nonexistent in the food supply. In some countries, such as the United States, iodine deficiency goiter (endemic goiter) has been virtually wiped out by fortifying table salt with iodide. Iodine deficiency, however, still affects upwards of 200 million people around the world.

Iodine is controversial for two reasons: breast, uterine, and ovarian cancer seem to be lower in areas of the world where iodine intake is high. Low intake of iodine may stimulate production of hormones which could help cause these forms of cancer. Keep in mind that this is only a theory based on studies of cancer death rates and iodine intake. Other factors obviously enter into the causation of cancer, and further experimentation is required before this theory is adequately tested.

The RDA for iodine is 150 micrograms (.15 mg.). Two grams of iodized salt supplies at least this amount.

Thyroid toxicity (thyrotoxicosis) has been reported to occur after administration of iodine supplements. Apparently, an excess of iodine results in the same physiological effect as a deficiency: hyperthyroidism. Many people react adversely to levels of iodine which are safe for most others, suggesting they have some metabolic defect which interferes with the regulation of the iodine-thyroid system. In addition to the stepped-up metabolism of hyperthyroidism and thyrotoxicosis, an excess of iodine can also cause acne.

The best natural sources of iodine are sea foods, including fish and seaweeds. A diet with plenty of these items does not need iodine supplementation. Baked goods and milk may also provide iodine, although it is not a natural part of the food, and is not a reliable source. Your baker may not use iodine compounds as dough conditioners; your dairy may not use iodine salt licks and disinfectants. Iodine is still an essential mineral. The best way to make sure you're getting enough, without increasing your salt intake, is to eat seafood.

Where is it found ?

Seafood, iodized salt, and sea vegetables-for example, kelp-are high in iodine. Processed food may contain added iodized salt. Iodine is frequently found in dairy products. Vegetables grown in iodine rich soil also contain this mineral.

Who is likely to be deficient ?

People who avoid dairy, seafood, processed food, and iodized salt can become deficient. Iodine deficiency can cause low thyroid function, goiter, and cretinism; however, iodine deficiencies are now uncommon in Western societies.

How much to take

Since the introduction of iodized salt, iodine supplements are unnecessary and not recommended for most people. For strict vegetarians who avoid salt and sea vegetables, 150 mcg per day is more than adequate.

Side effects

High doses (several milligrams per day) can interfere with normal thyroid function and should not be taken without consulting a nutritionally oriented doctor. The average diet provides about four times the recommended amount of iodine, which may result in health problems. In fact, goiter, traditionally a disease of iodine deficiency, is now linked sometimes to high iodine intake. Also, speculations of an iodine link to thyroid cancer have been reported. Some people react to supplemental iodine, the first symptom of which is usually an acne-like rash.

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