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Iodine constitutes about 0.00004% of the total human body weight. It is found in highest concentration in the thyroid gland, muscles, and various endocrine tissues. The primary function of iodine in the body is as a constituent of the hormones thyroxin and triiodotyrosine, both of which are secreted by the thyroid gland and affect growth, development, and the metabolic rate of the body.

Iodine, as a constituent of thyroxin, plays an important role in the efficient conversion of beta-carotene to vitamin A, with a subsequent increase in the efficacy of protein synthesis and cholesterol absorption.

Iodine deficiency is the primary cause of simple goiter and has been linked conclusively to cretinism.

Iodine is readily absorbed (almost 100%) from foodstuffs and is excreted in the urine.

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Method of Action

Iodine, upon absorption in the bloodstream, is concentrated within the thyroid gland by an active transport system called the "iodine pump." In the thyroid, iodine is oxidized to iodide by the enzyme iodine peroxidase. In this form, iodine is incorporated into tyrosine residues of the protein thyroglobulin proteins, whereupon it forms the active hormones thyroxin and triiodotyrosine.

Low thyroxin and triiodotyrosine levels in the body are "sensed" by the hypothalamus gland and stimulate the release of thyrotropin releasing hormone (TRH) from the hypothalamus. TRH stimulates the anterior pituitary to secrete thyroid stimulating hormone (TSH), which provokes processes that synthesize and release thyroxin and triiodotyrosine from the thyroglobulin protein. High thyroxin and triiodotyrosine levels provoke decrease TRH production, which slows the production of thyroxin and triiodotyrosine.

Thyroxin and triiodotyrosine enter the tissue cells of the body by passive diffusion. Increase adenosine triphosphate (ATP) consumption provokes an increased oxygen consumption and more expedient metabolism of glucose, lipids, and amino acids. The body then has an overall rise in basal metabolic rate.

High levels of thyroxin and triiodotyrosine can provoke an increase in the number and size of mitochondrial cells, with a possible inhibition of oxidative phosphorylation. This may result in an overall increase in body heat.

Goitrogens, natural inhibitors of the thyroid gland, can promote the development of goiter, a disorder characterized by an enlargement of the thyroid gland in the neck region. Goitrogens are found in cabbage, turnips, grape seeds, mustard, peanuts, cauliflower, and soybeans, as well as other food sources. Cooking is an adequate way of inactivating these compounds.

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Properties and Uses

Iodine has been used in the temporary treatment of hyperthyroidism (Grave’s disease). Hyperthyroidism is a disorder in which the thyroid is overactive, resulting in increased protein metabolism, calcium imbalance, glucose intolerance, and overall increased metabolism. Serum cholesterol and triglyceride levels are depressed, and the patient may complain of perspiration and heat intolerance. Iodine supplementation increases storage of the thyroid hormone thyroxine, helping to prevent its release.

Iodine supplements can be used for the prevention and cure of simple goiter, a disorder resulting from a deficiency in dietary iodine intake.

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Consequences of Deficiency

Insufficient iodine intake can, and quite frequently does, result in goiter. This condition is characterized by the swelling of the thyroid gland in the neck region. This swelling is a result of an increased proliferation of thyroid epithelial cells in order to compensate for low levels of thyroid hormones in the body. Symptoms of goiter include compression of the trachea (resulting in a hoarsening of the voice), chronic coughing, difficulty in swallowing, and facial congestion.

Severe iodine deficiencies in pregnant women can result in cretinism in the offspring, a disorder in which the child suffers from stunted growth or dwarfism, swollen facial features, and varying degrees of mental retardation.

Adults suffering from a surgically damaged thyroid may develop myxedema, a disorder with symptoms much resembling cretinism. These symptoms include lowered body temperature and pulse rate, lethargy, retardation of metabolic and mental processes, and a puffing of skin and tissues.

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Toxicity Levels

Excess dietary iodine is on the rise, and has many nutritionists concerned. These rises are attributed to: iodine in iodized salt found in many foods - especially prepackaged and fast foods; iodine in food supplements when the supplement taker takes double or triple doses thinking that if a little is good - more is even better (dangerous in this case); iodine added as a disinfectant to drinking water; iodine supplements given to livestock; iodine compounds used as dairy sanitizers; iodine used as a dough conditioner in bakeries. Amount over 500% of the RDA are considered to be dangerous and leads to a significant increase in the above outlined problems.

Excessive intake of iodine may result in a condition known as "iodine goiter." This type of goiter is characterized by an enlargement of the thyroid gland and might be erroneously diagnosed as goiter resulting from insufficient iodine intake. This condition is prevalent in Hokkaido, and island in norther Japan, where dietary intake of iodine rich seaweed and kelp are far in excess of RDA standards.

Research indicates that excess iodine may initially induce acne-like skin lesions or worsen preexisting acne and can result in the inhibition of thyroid hormone synthesis, with the effects being most pronounced in patients with hyperthyroidism.

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Recommended Dietary Allowances

RDA for men: 110 - 150 mcg
RDA for women: 80 - 115 mcg
RDA for child/adolescent: 60 - 110 mcg
RDA for infants: 40 mcg
RDA for pregnancy: 125 mcg
RDA for lactation: 150 mcg

Food Sources

Bread Butter Cheese Eggs
Fruits Kelp Meat Milk
Seafood Vegetables Prepackaged food Fast food
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