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Iodine is an essential trace element; the thyroid hormones thyroxine and triiodothyronine contain iodine. In areas where there is little iodine in the diet—typically remote inland areas where no marine foods are eaten—iodine deficiency gives rise to goiter (so-called endemic goiter), as well as cretinism, which results in developmental delays and other health problems.
While noting recent progress, The Lancet noted, "According to World Health Organization, in 2007, nearly 2 billion individuals had insufficient iodine intake, a third being of school age. ... Thus iodine deficiency, as the single greatest preventable cause of mental retardation, is an important public-health problem."
In some such areas, this is now combated by the addition of small amounts of iodine to table salt in form of sodium iodide, sodium iodate, potassium iodide, and/or potassium iodate—this product is known as iodized salt. Iodine compounds have also been added to other foodstuffs, such as flour, water and milk in areas of deficiency. Seafood is also a well known source of iodine. Thus, iodine deficiency is more common in mountainous regions of the world where food is grown in iodine-poor soil.
Signs and symptoms 
A low amount of thyroxine (one of the two thyroid hormones) in the blood, due to lack of dietary iodine to make it, gives rise to high levels of thyroid stimulating hormone (TSH), which stimulates the thyroid gland to increase many biochemical processes; the cellular growth and proliferation can result in the characteristic swelling or hyperplasia of the thyroid gland, or goiter. In mild iodine deficiency, levels of triiodiothyronine (T3) may be elevated in the presence of low levels of levothyroxine, as the body converts more of the levothyroxine to triiodothyronine as a compensation. Some such patients may have a goiter, without an elevated TSH. The introduction of iodized salt since the early 1900s has eliminated this condition in many affluent countries; however, in Australia, New Zealand, and several European countries, iodine deficiency is a significant public health problem. It is more common in third-world nations. Public health initiatives to lower the risk of cardiovascular disease have resulted in lower discretionary salt use at the table. Additionally, there is a trend towards consuming more processed foods in western countries. The noniodized salt used in these foods means that people are less likely to obtain iodine from adding salt during cooking.
Goiter is said to be endemic when the prevalence in a population is > 5%, and in most cases goiter can be treated with iodine supplementation. If goiter is untreated for around five years, however, iodine supplementation or thyroxine treatment may not reduce the size of the thyroid gland because the thyroid is permanently damaged.
Iodine deficiency is one of the leading causes of preventable mental handicaps worldwide, producing typical reductions in IQ of 10 to 15 IQ points. It has been speculated that deficiency of iodine and other micronutrients may be a possible factor in observed differences in IQ between ethnic groups: see race and intelligence for a further discussion of this controversial issue.
Cretinism is a condition associated with iodine deficiency and goiter, commonly characterised by mental deficiency, deaf-mutism, squint, disorders of stance and gait, stunted growth and hypothyroidism. Paracelsus was the first to point out the relation between goitrous parents and mentally retarded children.
As a result of restricted diet, isolation, intermarriage, etc., as well as low iodine content in their food, children often had peculiar stunted bodies and retarded mental faculties, a condition later known to be associated with thyroid deficiency. Diderot, in his 1754 Encyclopédie, described these patients as "crétins". In French, the term "crétin des Alpes" also became current, since the condition was observed in remote valleys of the Alps in particular. The word cretin appeared in English in 1779.
In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency gives rise to hypothyroidism, symptoms of which are extreme fatigue, goiter, mental slowing, depression, weight gain, and low basal body temperatures.
Iodine deficiency is the leading cause of preventable mental retardation, a result which occurs primarily when babies or small children are rendered hypothyroidic by a lack of the element. The addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but as of March 2006, iodine deficiency remained a serious public health problem in the developing world. Iodine deficiency is also a problem in certain areas of Europe. In Germany it has been estimated to cause a billion dollars in health care costs per year.
Iodine may also help prevent diseases of the oral and salivary glands.
Risk factors 
Following is a list of potential risk factors that may lead to iodine deficiency:
- Low dietary iodine
- Selenium deficiency
- Exposure to radiation
- Increased intake/plasma levels of goitrogens, such as calcium
- Gender (higher occurrence in women)
- Smoking tobacco
- Alcohol (reduced prevalence in users)
- Oral contraceptives (reduced prevalence in users)
- Age (for different types of iodine deficiency at different ages)
Iodine accounts for 65% of the molecular weight of T4 and 59% of the T3. 15–20 mg of iodine is concentrated in thyroid tissue and hormones, but 70% of the body's iodine is distributed in other tissues, including mammary glands, eyes, gastric mucosa, arterial walls, the cervix, and salivary glands. In the cells of these tissues, iodide enters directly by sodium-iodide symporter (NIS).
- Venturi S, Guidi A, Venturi M. (1996). [Extrathyroid iodine deficiency disorders: what is the real iodine requirement?]". Le Basi Razionali della Terapia 16:267-275.
- Pellerin P (1961). "La tecnique d'autoradiographie anatomique a la temperature de l'azote liquide". Path Biol 232 (9): 233–252.
- Byeong-Cheol Ahn (2011). "Physiologic and False Positive Pathologic Uptakes on Radioiodine Whole Body Scan".
The diagnostic workup of a suspected iodine deficiency includes signs and symptoms as well as possible risk factors mentioned above.
In addition, a 24-hour urine iodine collection is a useful medical test, as approximately 90% of ingested iodine is excreted in the urine. If a 24-hour urine collection is not practical, a random urine iodine-to-creatinine ratio can alternatively be used.
Iodine deficiency is treated by ingestion of iodine, such as found in food supplements. Mild cases may be treated by using iodized salt in daily food consumption, or drinking more milk; or eating egg yolks, and saltwater fish. Iodized salt offers sufficient amounts of iodine. For a salt and/or animal product restricted diet, sea vegetables (kelp, hijiki, dulse, nori (found in sushi)) may be incorporated regularly into a diet as a good source of iodine.
In an adult, 150 µg/d is sufficient for normal thyroid function. However, because of the additional requirements of women, it is recommended that higher intake levels of 150-300 µg/d should be ingested daily.
Iodine deficiency resulting in goiter occurs 187 million people globally as of 2010 (2.7% of the population). Certain areas of the world, due to natural deficiency and unavailability of iodine, are severely affected by iodine deficiency, which affects approximately two billion people worldwide. It is particularly common in the Western Pacific, South-East Asia and Africa. Among other nations affected by iodine deficiency, China and Kazakhstan have begun taking action, while Russia has not. Successful campaigns for the adoption of the use of iodized salt require education of salt producers and sellers and a communication campaign directed at the public. The cost of adding iodine to salt is negligible—"Only a few cents a ton."
Iodine deficiency has largely been confined to the developing world for several generations, but reductions in salt consumption and changes in dairy processing practices eliminating the use of iodine-based disinfectants have led to increasing prevalence of the condition in Australia and New Zealand in recent years. A proposal to mandate the use of iodized salt in most commercial breadmaking was adopted there in October, 2009.. In a study of the United Kingdom published in 2011, almost 70% of test subjects were found to be iodine deficient. The study's authors suggested an investigation regarding "evidence-based recommendations for iodine supplementation".
With iodine supplementation, goiters caused by iodine deficiency decrease in size in very young children and pregnant women. Generally, however, long-standing goiters caused by iodine deficiency respond with only small amounts of shrinkage after iodine supplementation, and patients are at risk for developing hyperthyroidism.
See also 
- The Lancet (12 July 2008). "Iodine deficiency—way to go yet". The Lancet 372 (9633): 88. doi:10.1016/S0140-6736(08)61009-0. PMID 18620930. Retrieved 2008-12-05.
- François Delange, Basil Hetzel. "The Iodine Deficiency Disorders". Thyroid Disease Manager.
- Iodine in Seaweed
- Andersson M, Takkouche B, Egli I, Allen HE, de Benoist B (2005). "Current global iodine status and progress over the last decade towards the elimination of iodine deficiency". Bull. World Health Organ. 83 (7): 518–25. PMC 2626287. PMID 16175826.
- T. E. C. Jr. M.D. (August 1, 1974). "Paracelsus on What the Physician Should Know". Pediatrics (American Academy of Pediatrics) 54 (2): 141. Retrieved 2008-12-05.
- Felig, Philip; Frohman, Lawrence A. (2001). "Endemic Goiter". Endocrinology & metabolism. McGraw-Hill Professional. ISBN 978-0-07-022001-0.
- "Micronutrients — Iodine, Iron and Vitamin A". UNICEF.
- Patrick L (2008). "Iodine: deficiency and therapeutic considerations". Altern Med Rev 13 (2): 116. PMID 18590348.
- Venturi, S.; Venturi, M. (2009). "Iodine in evolution of salivary glands and in oral health". Nutrition and health (Berkhamsted, Hertfordshire) 20 (2): 119–134. doi:10.1177/026010600902000204. PMID 19835108.
- Knudsen N, Laurberg P, Perrild H, Bülow I, Ovesen L, Jørgensen T (October 2002). "Risk factors for goiter and thyroid nodules". Thyroid : Official Journal of the American Thyroid Association 12 (10): 879–88. doi:10.1089/105072502761016502. PMID 12487770.
- medscape > Iodine Deficiency Authors and editors: Stephanie L Lee and George T Griffing. Updated: Apr 22, 2009
- "Mortality and Burden of Disease Estimates for WHO Member States in 2002" (xls). World Health Organization. 2002.
- Vos, T (2012 Dec 15). "Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010.". Lancet 380 (9859): 2163–96. PMID 23245607.
- "In Raising the World’s I.Q., the Secret's in the Salt", article by Donald G. McNeil, Jr., The New York Times, December 16, 2006.
- l "Iodine Fortification", article appearing on March 5, 2013 from Food Standards.
- "Iodine status of UK schoolgirls: a cross-sectional survey". The Lancet 377 (9782): 2007–12. 11 June 2011. doi:10.1016/S0140-6736(11)60693-4. PMID 21640375.
- International Council for the Control of Iodine Deficiency Disorders
- Can Africa meet the goal of eliminating iodine-deficiency disorders by the year 2000?
- Kotwal A, Priya R, Qadeer I (2007). "Goiter and other iodine deficiency disorders: A systematic review of epidemiological studies to deconstruct the complex web". Arch. Med. Res. 38 (1): 1–14. doi:10.1016/j.arcmed.2006.08.006. PMID 17174717.
- "Iodine and adult IQ"