About one third of the iodine present in adults occurs in the thyroid gland. It is about 20-25 mg. The concentration of this in the thyroid is about 2500 times greater than in any other body tissue.
Iodine is ingested in food as inorganic iodides and as organic compounds. During the process of digestion, iodine is split from organic compounds and is absorbed as inorganic iodides. The degree of absorption depends upon the level of the thyroid hormone circulating in the blood. The blood transport iodine as free iodine and as protein bound iodine or PBI, which is sensitive to the changes in the level of thyroid activity. It rises during pregnancy and with hyper activity of the gland. The measurement of PBI is a specific diagnosis for the thyroid activity, now replacing the former basal metabolic test.
Thyroid activity is controlled by the thyroid –stimulating hormone or TSH which is secreted by the anterior lob of the pituitary gland. This helps to bring about release and withdrawal of iodine from the blood circulation during cellular oxidation. About one third of the iodine thus released is retained to be used again as thyroid hormone and the remainder is excreted through urine.
It is constituent of the thyroid gland which controls the rate of energy utilized in the body or the BMR. Iodine is essential for synthesis of thyroid hormone, thyroxin. In the thyroid gland the complex organic iodine is oxidized to element iodine which then binds with tyrosine to form mono and –Di-iodotyrosines. The epithelial cells of the gland convert iodotyrosines to thyroxin. Thyroxin is bound to the globulin and is stored as thryoglobin in the gland. Thyroxine regulates the rate of oxidation within the cells thereby stimulating physical and mental growth, functioning of nerve and muscle tissue, circulation of blood and metabolism of all nutrients
Iodine is generally supplied by food and water, provided the soil contains it. People living in coastal areas and eating sea fish ingest enough iodine for their needs. In hilly areas where there is deficiency of iodine in food and drinking water, Iodization of salt is the only technique available to make good this deficiency in order to prevent endemic goiter. Sodium or potassium iodide is used for iodization is not possible, another method is employed by injecting iodised oil into the muscles. Iodised poppy seed oil contains 37 per cent of iodine. It is cheap, long acting and relatively free from side effects.
The daily requirement for iodine range from 100mg to 150mg. The requirement s increases during pregnancy, lactation and periods of rapid growth. These daily requirements are supplied by food and water except in hilly regions where there is a deficiency of iodine in both soil and water.
Deficiency of iodine (Hypothyrodism)
Endemic goiter, the iodine deficiency disease, occurs in certain part of the world where the soil has low iodine content. As a result the food and water also became deficient in iodine in these areas. The general great lakes, the pacific North West Switzerland, Central American countries, mountainous region of s. America and New Zealand are known for endemic goiter.
Endemic goiter is a public health problem in India in the sub- Himalayan areas, Maharashtra and the sub Vindhya region (Aurangabad) Where 50 per cent have goiter. These areas from the goiter belt of our country.
Goiter is characterized by the swelling of thyroid gland. The reduced secretion of the thyroid gland controls the state of the connective tissue. Deficiency of thyroxin reduces the carbohydrate oxidation resulting in the accumulation of mucopolysaccharides that give the person a myxodemic appearance.
Due to the over activity of thyroid gland there is excessive oxidation of food. The individual with a hyperactive thyroid will be lean restless, perpetually hungry, having popping eye. The presence of natural inhibitor of thyrosine in cabbage, turnips, mustard and rapeseed helps to overcome hyperthyroidism.