Why is Iodine added to Salt?

saltWhen back in 1811 Bernard Courtois noticed the violet fumes produced when his seaweed extraction tank was being cleaned, he could have never dreamed that he had set the stage for one of the most important nutritional interventions in history. Let’s backtrack a little. Courtois owned a factory that produced potassium nitrate, better known as saltpetre. This substance was a major component of gunpowder and was in great demand by the military. One source of potassium nitrate was vegetable matter and Courtois had found that decaying seaweed fit the bill nicely. But the large tanks used to extract the seaweed had to be periodically cleaned, a difficult procedure that required the use of acids. When one day a particularly large amount of acid was used, violet fumes appeared and condensed on the cold surfaces of the tank into dark metallic-looking crystals. A sample of this found its way into the hands of Joseph-Louis Gay Lussac, one of the most noted French scientists of the era. He was intrigued by the stuff, but was really energized into studying it thoroughly when he heard that Sir Humphrey Davy, the brilliant English chemist who was visiting France upon a special invitation by Napoleon, had also been given a sample. Gay-Lussac didn’t want an Englishman to make some big discovery from a French product. Independently, both men came to the conclusion that the violet crystals constituted a new element which Gay-Lussac named “iode” from the Greek for violet. Davy suggested iodine, to make the name conform with chlorine, to which it was similar.

Iodine turned out to have some disinfectant properties, but that is not its main claim to fame. Iodine is an essential nutrient, required by the thyroid gland to produce thyroxine, a hormone that controls many body functions, including brain acuity. A deficiency of iodine in the diet leads to an enlargement of the thyroid gland, known as goiter, and in extreme cases causes cretinism and dwarfism. But even mild cases of iodine deficiency can cause mental retardation. Indeed, iodine deficiency is regarded as the leading preventable cause of mental retardation. A small deficiency in pregnant women or infants can lower IQ scores by 10-15 points. It is estimated that about 2 billion people suffer from iodine deficiency in the world, and the real tragedy is that the condition is so readily preventable. Addition of potassium iodate to salt is the simple solution. About $1.15 worth added to each ton of salt solves the problem. Progress is being made: in 1990 only about 25% of the world’s households consumed iodized salt, now more than two thirds do. The simple measure of adding iodine to salt is perhaps the most effective way to increase the world’s cumulative intelligence.

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