Editing Thyroid (section)

====Iodine====
{{Further|Iodine in biology}}
[[File:The thyroid gland in health and disease (1917) (14780980651).jpg|thumb|Child affected by [[Congenital iodine deficiency syndrome]], associated with a lack of iodine.<ref>The thyroid gland in health and disease Year: 1917 [[Robert McCarrison]]</ref>]]
[[Iodine deficiency]], most common in inland and mountainous areas, can predispose to goitre – if widespread, known as [[endemic goitre]].{{sfn|Greenspan's|2011|p=164}} Pregnant women deficient of iodine can give birth to infants with thyroid hormone deficiency.{{sfn|Greenspan's|2011|p=164}}<ref name=":1" /> The use of [[iodised salt]] to add iodine to the diet<ref name=":1" /> has eliminated [[endemic cretinism]] in most developed countries,<ref>{{Cite book|url=https://books.google.com/books?id=sX-HCgAAQBAJ&q=iodine+supplementation+has+eliminated+cretinism&pg=PA268|title=Global Epidemiology of Cancer|last=Harris|first=Randall E. | name-list-style = vanc |date=2015-05-07|publisher=Jones & Bartlett Publishers|isbn=978-1-284-03445-5|page=268|language=en}}</ref> and over 120 countries have made the iodination of [[salt]] mandatory.<ref>{{cite journal | vauthors = Leung AM, Braverman LE, Pearce EN | title = History of U.S. iodine fortification and supplementation | journal = Nutrients | volume = 4 | issue = 11 | pages = 1740–6 | date = November 2012 | pmid = 23201844 | pmc = 3509517 | doi = 10.3390/nu4111740 | doi-access = free }}</ref><ref name=Map>{{cite web|url=https://fortificationdata.org/map-number-of-nutrients/|title=Map: Count of Nutrients In Fortification Standards|website=Global Fortification Data Exchange|access-date=23 December 2019}}</ref>

Because the thyroid concentrates iodine, it also concentrates the various radioactive [[isotope]]s of iodine produced by [[nuclear fission]]. In the event of large accidental releases of such material into the environment, the uptake of radioactive iodine isotopes by the thyroid can, in theory, be blocked by saturating the uptake mechanism with a large surplus of [[Radiation pill|non-radioactive iodine]], taken in the form of potassium iodide tablets. One consequence of the [[Chernobyl disaster]] was an increase in [[thyroid cancer]]s in children in the years following the accident.<ref>{{cite news| url=http://news.bbc.co.uk/hi/english/sci/tech/newsid_1319000/1319386.stm | work=BBC News | title=Chernobyl children show DNA changes | date=2001-05-08 | access-date=2010-05-25}}</ref>

Excessive iodine intake is uncommon and usually has no effect on the thyroid function. Sometimes though it may cause hyperthyroidism, and sometimes hypothyroidism with a resulting goitre.<ref name="MSD">{{cite web |title=Iodine - Disorders of Nutrition |url=https://www.msdmanuals.com/en-gb/home/disorders-of-nutrition/minerals/iodine |website=MSD Manual Consumer Version |access-date=18 December 2019 |archive-date=18 December 2019 |archive-url=https://web.archive.org/web/20191218133539/https://www.msdmanuals.com/en-gb/home/disorders-of-nutrition/minerals/iodine |url-status=dead }}</ref>