Iodised Salt - Chemistry, Biochemistry and Nutritional Aspects

Chemistry, Biochemistry and Nutritional Aspects

Four inorganic compounds are used as iodide sources, depending on the producer: potassium iodate, potassium iodide, sodium iodate, and sodium iodide. Any of these compounds supplies the body with its 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.

Edible salt can be iodised by spraying it with a potassium iodate solution. 60 ml of potassium iodate, costing about US$1.15 (in 2006), are required to iodise a ton of salt. 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 1952, 7.5 mg/kg in 1962, 15 mg/kg in 1980, and 20 mg/kg in 1998. 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. The halogen iodide, over time and exposure to excess oxygen and carbon dioxide, slowly oxidises to metal carbonate and elemental iodine, which then evaporates.