Iodised salt (also spelled iodized salt) is table salt mixed with a minuscule amount of various iodine salts. The ingestion of iodine prevents iodine deficiency. Worldwide, iodine deficiency affects about two billion people and is the leading preventable cause of intellectual and developmental disabilities. Deficiency also causes thyroid gland problems, including endemic goitre. In many countries, iodine deficiency is a major public health problem that can be cheaply addressed by purposely adding small amounts of iodine to the sodium chloride salt. Iodine is a micronutrient and dietary mineral that is naturally present in the food supply in some regions (especially near sea coasts) but is generally quite rare in the Earth's crust. Where natural levels of iodine in the soil are low and vegetables do not take up the iodine, iodine added to salt provides the small but essential amount of iodine needed by humans. An opened package of table salt with iodide may rapidly lose its iodine content in high temperature and high relative humidity conditions through the process of oxidation and iodine sublimation. Poor manufacturing techniques and storage processes can also lead to insufficient amounts of iodine in table salt.
Chemistry, biochemistry, and nutritional aspects
Four inorganic compounds are used as iodine sources, depending on the producer: potassium iodate, potassium iodide, sodium iodate, and sodium iodide. Any of these compounds supplies the body with the iodine required for the biosynthesis of thyroxine (T4) and triiodothyronine (T3) hormones by the thyroid gland. Animals also benefit from iodine supplements, and the hydrogen iodide derivative of ethylenediamine is the main supplement to livestock feed. Salt is an effective vehicle for distributing iodine to the public because it does not spoil and is consumed in more predictable amounts than most other commodities. For example, the concentration of iodine in salt has gradually increased in Switzerland: 3.75 mg/kg in 1922, 7.5 mg/kg in 1962, 15 mg/kg in 1980, 20 mg/kg in 1998, and 25 mg/kg since 2014. These increases were found to improve iodine status in the general Swiss population. Salt that is iodised with iodide may slowly lose its iodine content by exposure to excess air over long periods. Salts fortified with iodate are relatively stable to storage and heat; the main concern is reducing impurities in the salt itself, which can be removed relatively easily. Moisture accelerates the decomposition of iodate, but ceases to do so once reducing impurities are removed. Contrary to popular assumptions, iodised salt cannot be used as a substitute for potassium iodide (KI) to protect a person's thyroid gland in the event of a nuclear emergency. There is not enough iodine in iodised salt to block the uptake of radioactive iodine by the thyroid.
Production
Edible salt can be iodised by spraying it with a potassium iodate or potassium iodide solution. 57 grams of potassium iodate, costing about US$1.15 (in 2006), is required to iodise a short ton (2,000 pounds) of salt. Optional additives include:
Stabilisers such as dextrose (typically at about 0.04%) and sodium thiosulfate, which prevent potassium iodide from oxidizing and evaporating. These ingredients are not required for potassium iodate, which is commonly used globally for its increased stability, but is not approved by the US FDA. Anti-caking agents such as calcium silicate and sodium ferrocyanide, which prevent clumping.
Public health initiatives
Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual and developmental disabilities. According to public health experts, iodisation of salt may be the world's simplest and most cost-effective measure available to improve health, only costing US$0.05 per person per year. At the World Summit for Children in 1990, a goal was set to eliminate iodine deficiency by 2000. At that time, 25% of households consumed iodised salt, a proportion that increased to 66% by 2006. Salt producers are often, although not always, supportive of government initiatives to iodise edible salt supplies. Opposition to iodisation comes from small salt producers who are concerned about the added expense, private makers of iodine pills, concerns about promoting salt intake, and unfounded rumours that iodisation causes AIDS or other illnesses. The United States Food and Drug Administration recommends 150 micrograms (0.15 mg) of iodine per day for adults. While iodine is crucial, the FDA also recommends limiting overall sodium intake to less than 2,300 mg per day for adults, which is approximately 1 teaspoon of table salt.
Argentina Since 8 May 1967 salt for human or animal use must be iodised, according to the Law 17,259.
Australia Australian children were identified as being iodine deficient in a survey conducted between 2003 and 2004. As a result of this study the Australian Government mandated that all bread except "organic" bread must use iodised salt. There remains concern that this initiative is not sufficient for pregnant and lactating women.
Brazil Iodine Deficiency Disorders were detected as a major public health issue by Brazilian authorities in the 1950s when about 20% of the population had a goitre. The National Agency for Sanitary Vigilance (ANVISA) is responsible for setting the mandatory iodine content of table salt. The Brazilian diet averages 12 g of table salt daily, more than twice the recommended value of 5 g daily. To avoid excess consumption of iodine, the iodizing of Brazilian table salt was reduced to 15–45 mg/kg in July 2013. Specialists criticised the move, saying that it would be better for the government to promote reduced salt intake, which would solve the iodine problem as well as reduce the incidence of high blood pressure.
Canada For table and household use, salt sold to consumers in Canada must be iodised with 0.01% potassium iodide. Sea salt and salt sold for other purposes, such as pickling, may be sold uniodised.
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