Iodine is a constituent of the thyroid gland which controls the rate at which energy is used up in the body. It is present in the body in minute amounts about 15 to 23 mg. It is ingested in foods as inorganic iodides and as organic compound.
Apart from controlling the rate of energy utilization in the body, iodine is essential for synthesis of the thyroid hormones, thyroxin. Thyroxin 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.
Both foods and water provide iodine in the human diet. The amount present in the water varies from one area to another, and tends to parallel the iodine content of the soil. 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, iodisation of salt is the only technique available to make good of this deficiency. Sea fish, Oysters, seaweeds and vegetables grown on soils containing iodine are the richest dietary sources.
Iodine requirements of adults are about 0.2 mg. daily.
If sufficient iodine is not taken on the diet, enlargement of the thyroid gland takes place resulting in a disease called goiter. Subnormal basal metabolism, sometimes associated with over weight, lowered mental ability, nervousness and sluggish movements are symptoms of iodine deficiency.