Iodine is a trace element that is essential for the synthesis of thyroid hormones in vertebrates, although iodoproteins are are present in invertebrates. Some regions of the world are naturally deficient in iodine due to the low availability of iodine from their soil or other climatic and environmental factors affecting iodine availability.

Iodine is an essential trace element for humans. The average adult has between 20 and 50 milligrams of iodine. Approximately 60% of the iodine is in the thyroid gland, which is located in the base of the neck. The rest of the iodine is in the thyroid hormone, ovary and muscle. The distribution of iodine in the world varies greatly, so that the food that grows in areas with a low concentration of iodine does not contain enough of the micronutrient. These areas are located in Central America, parts of China, Continental Europe, Russia and South America.

Physiological role of iodine

Iodine is a component of the thyroid hormones thyroxine and triiodothyronine that determine the rate of metabolism in the body. This refers to the conversion of food into energy in the body, and also how to use that energy.

Thyroid hormones are essential for the growth and development of organs, particularly the brain, reproductive system, nervous system, bones, skin, hair, nails and teeth. The thyroid gland is involved in the production of proteins, cholesterol synthesis, carbohydrate absorption and the conversion of carotene to vitamin A.

Thyroxine is important for the regulation of body weight.

Metabolism

Iodine is absorbed in the small intestine, and the excess is eliminated in the urine.

Food sources of iodine

Good sources of iodine are vegetable that grows on the soil rich with iodine. The iodine present in the upper crust of earth is leached by glaciation and repeated flooding and is carried to the sea. Sea water is, therefore, a rich source of iodine. The seaweed located near coral reefs has an inherent biologic capacity to concentrate iodine from the sea. The reef fish which thrive on seaweed are rich in iodine. Apart from sea food; onions, chokeberry, milk and milk products are rich in iodine. Sodium or potassium iodide is added to salt in many countries. Iodine content in food products

Recommended daily allowance

Iodine deficiency

Lack of iodine in the body leads to a number of different diseases, such as hypothyroidism, goiter and cretinism. If the daily intake of iodine is less than 50 micrograms the deficiency occurs.

When the storage of iodine in the body depleted thyroid gland located in the neck comes under the influence of the pituitary gland, increases its activity and starts to increase. This phenomenon is called a goiter. Other symptoms of hypothyroidism include fatigue, apathy, drowsiness, vulnerability values are presented to cold, lethargy, muscle weakness, increasing body weight and skin becomes rougher. Young people who live in areas where there is a lack of iodine are at risk of developing goiter.

Iodine deficiency is a significant global problem, but it is relatively rare in industrialized countries due to salt iodine which is used in the diet. People who consume too much food, which prevents the utilization of iodine incidence of goiter. These foods include raw cabbage, kale, turnips, peanuts, soybeans, cauliflower. Some medications, such as disulfiram, thiouracil, thiourea and sulfonamide can also inhibit the thyroid gland and lead to a lack of iodine in the body. Reducing the amount of salt that enters the body in combination with a higher intake of industrially prepared food which uses a small amount of iodinated salt can also lead to a lack of iodine in the body.

Thyroid hormones are needed during pregnancy due to the normal nervous development of the fetus. If in women during pregnancy occurs iodine deficiency it increases the risk of miscarriage and dead born child. If the infant is borne at term it can cause irreversible mental retardation. This is known as (cretinism) and is a major cause of preventive acting in areas with low iodine.

If in a child is present moderate iodine deficiency then appear less mental capacity and poor motivation. Developing fetus, newborn and young children are most vulnerable to food which does not have enough iodine, so treatment before conception or early in pregnancy is essential for the protection of irreversible damage. Breast milk contains more iodine than infant formula milk, and therefore if a child is born prematurely and fed with infant formula it is exposed to a greater risk of iodine deficiency.

Iodine plays an important role in fibrocystic breast disease. Hypothyroidism and iodine deficiency increases the risk of breast cancer.

The spectrum of iodine deficiency disorders

Overdose

Excess iodine intake is more difficult to define. Many people regularly ingest huge amounts of iodine - in the range 10-200 mg/day – without apparent adverse effects. Symptoms of acute poisoning of absorbed iodine (rather than iodidte) caused by its corrosive effects on the gastrointestinal tract, include vomiting, abdominal pain and diarrhea. Other symptoms may be a metallic taste in the mouth, pain in the teeth, gums and mouth as well as severe headaches. Finally, and kidneys stop producing urine. The lethal dose is 2-3 grams of iodine. If someone notice symptoms of excess iodine they need to be treated with large amounts of milk, starch solution and a 1% solution of potassium thiosulphate.

Toxic effects of iodide (unlike iodine) are rare and may cause reduction in the secretion of thyroid hormones, acne, and inflammation of the salivary gland if quantities exceed more than 1500 micrograms. Daily iodine intake should not be more than 1000 micrograms per day. Toxic effects may result from high intake that can occur during medical treatments. Patients may become hypersensitive if iodine is intaked for a long period.

Iodine in medicine

Iodine in medicine is used for the treatment of disease caused by lack of iodine. Most iodine is added in the form of iodized salt or iodized oil injection.

Some studies have shown that iodine treatment can reduce symptoms of fibrocystic breast disease.

Iodine is a good antiseptic and can be used to kill bacteria and fungi. Therefore, the use of a wide range of showering microorganisms including Candida and Chlamydia. Excessive intake of iodine is not good because it can reduce thyroid function.

Iodine in the form of tablets can be used to disinfect water.

In nuclear accidents radioactive iodine is released into the atmosphere. The use of radioactive iodine the thyroid gland can cause the occurrence of cancer. Treatment with iodine can preventively act on radioactive intake of iodine.

References

Frieden E., 1984, “Biochemistry of the essential ultratrace elements,” Plenum press, New York [Web Reference]

Frieden E., 2012, “ed. Biochemistry of the essential ultratrace elements. Vol. 3,” Springer Science & Business Media; [Web Reference]

Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001. 8, Iodine. [Web Reference]

Koutras D.A., Matovinovic J. and Vought R., 1985, “The ecology of iodine. In: Stanbury J.B., Hetzel B.S. (eds). Endemic goitre and cretinism, iodine nutrition in health and disease,” p. 185-95. New York: Wiley Eastern Limited.

Soetan K.O., Olaiya C. O. and Oyewole O.E., 2010, “The importance of mineral elements for humans, domestic animals and plants-A review,” African Journal of Food Science; 4(5): 200-222. [Web Reference]