Most of the body iodine is present in the thyroid gland, but all cells contain trace amount of iodine. Iodine is a constituent of two hormones, thyroxine (T4) and triiodothyroxine (T3). These hormones (i) regulate energy metabolism, (ii) synthesis of proteins and cholesterol and in the conversion of carotene to vitamin A.
The amount of iodine in plant food depends on whether or not iodine was present in the soil in which the plants were grown. Vegetables grown in iodine-rich soil will naturally be the good sources of iodine. The animal sources of iodine include milk, sea fish, shell fish and crabs.
For adults are about 0.10 to 0.15 mg/day for infants and children 0.05 to 0.10 mg/day. This is normally supplied by an ordinary well balanced diet and by drinking water except in mountainous regions where the food and water are deficient in iodine content. Drinking and cooking water often contain iodine in sufficient quantities to provide the daily requirement. Iodised salt may be added when cooking foods in areas with insufficient natural sources of iodine.
Adults - 100-150 μg/day
Pregnant women - 200 μg/day
Absorption is through the villi of the small intestine into the blood stream and 90 percent of the iodine of the thyroid gland is in organic combination and stored in the follicular colloids as thyroglobulin.
Inorganic iodine is mostly excreted by the kidneys, liver, skin, lungs and intestine and in milk. About 10 percent of circulating organic iodine is excreted in feces.
A deficiency of iodine leads to a decreased production of thyroxine, and inturn a lowered rate of energy metabolism. In an attempt to produce more thyriod hormones the thyroid gland enlarges. This condition is called simple or endemic goiter. In a mild deficiency the only symptom noted is slight enlargement of the thyroid gland visible at the neckline. However, if the condition persists, the women who has a simple goiter and who fails to get sufficient iodine during pregnancy will be unable to supply the fetus with its needs: thus, the baby is more severely affected than its mother.
People born in areas which lack of iodine in the water and soil have a tendency to develop ‘goitre’, a condition characterised by subnormal metabolic activities. The condition may be reversed if treated sufficiently with iodine at the early stage itself.