Iodine as Mineral – Rich Food Sources, Functions, Deficiency & Daily Requirements for Children, Men & Women

Presentation Notes on Iodine (I) Vegetarian & Non Vegetarian Food Sources, Recommended Dietary allowance, Iodine deficiency disorders, Role in Human Body with Treatment in word / .doc / ppt format

Iodine:

It is an essential component of thyroid hormones (T3 and T4).

Sources:

• Iodized table salts, flesh and oil of marine fish, onion, iodate-enriched bread.

Daily requirement:

• Adult man: 140mg; adult women: 100mg.
• Adolescent boy: 150mg; adolescent girl: mg.
• Pregnant woman: 125mg; lactating woman: 150mg.
• Children: 60-100mg.

Incorporation of iodine:

• Concentration of iodine occurs in the thyroid follicle actively, with the help of a NA + K+- ATPase pump.
• This iodide (I-) is then oxidized to iodine (I+) with the help of peroxidase.
• Iodination of the tyrosine residues of the protein thyroglobulin now occurs.
• Thyroglobulin, a glycoprotein, contains approximately 5000 amino acids. 115 tyrosine residues present.

Absorption and metabolism:

• Free iodine and inorganic iodate are first converted to iodide which are easily absorbed from gastrointestinal tract.
• Iodides can also be absorbed from mucous membrane, lungs and skin.
• Thyroid hormones, i.e., triiodothyronine (T3) and tetraiodothyronine (T4) are iodinated derivatives of the amino acid, thyronine.
• In the thyroid gland, iodine is taken up by the active transport and oxidized to active iodine.
• The active iodine is then utilized to iodinate tyrosine to form iodotyrosine.
• Iodotyrosine residues are then coupled to form T3 and T4.

Functions of iodine:

• Iodine is required for the synthesis of hormones, T3 and T4. Iodine acts only when it is  synthesized and it carries out the following functions :

-          Increases metabolism and oxygen consumption of tissues. Increases basal metabolic rate.

-          Increases conversion of glycogen to glucose leading to increase in blood sugar level.

-          Increases heart rate.

-          Depletes calcium and phosphorus of bones and increases urinary calcium excretion. 

Excretion:

• Liver, kidneys, muscles and heart deaminate iodothyronine to iodothyropyruvate. This is then decarboxylated to iodothyroacetate. Deiodination occurs in peripheral tissues.
• Detoxication is carried out by methylation or conjugation with glucuronic and sulphuric acids excreted in bile and urine.

Circulation of T3 and T4:

Iodine deficiency:

• It leads to still births, abortions, congenital heart anomalies, endemic cretinism, mental retardation and neurological defects. Treatment of iodine deficiency before pregnancy prevents disorders in children.

Applied aspects:

• Goitre is the enlargement of thyroid gland. There are normal, hypo and hyperthyroid states. Simple goitre results in decreased thyroxine production. It occurs due to defect in the steps for production of thyroid hormones.
• Simple endemic goitre occurs due to inadequate supply of iodine, hypothyroidism and myxoedema in adults.
• Myxoedema is due to hypothyrodisim in adults. Basal metabolic rate and body temperature are lowered and memory is poor in this disease.
• Cretinism is due to incomplete development or congenital absence of thyroid gland. It is evident in children. Children are dwarfed, mentally retarded and have protruding tongue and pot bellies.

Hyperthyroidism:

• Expoththalmus, enlarged and hyperactive thyroid.
• Grave’s disease results from increased production of thyroid stimulating immunoglobin (TSI) that activates TSH receptor, LATS (long-acting thyroid stimulating factor).
• Hahimoto’s disease. Occurs due to destruction of thyroid tissues, effects of antithyroid antibiotics, overproduction of TSH and hyperthyroidism.

Applied aspects:

• Antithyroid substances such as cabbages, turnip, soyabean cause simple goitre. Goitrogenic substances contain L-5-viny-2-thiooxazolidone.
• Radioiodine studies. radioiodine uptake studies are undertaken to determine the overall activity of the gland, particularly in hyperthyroidism. Trace doses of I125 or I131 are administered orally and percentage of iodine taken up by thyroid gland is measured by counting a-rays at standard time intervals.
• In patients with Grave’s disease, thyroid uptake is measured before and after an 8-day course of iodinated T3 administration. No decline in uptake is observed.

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