Discovered by Bernard Courtois (1777-1838) in 1811, iodine is a trace element, essential to (human) life, found in rocks, seawater and some types of soil. Sea fish and shell fish are also good sources of iodine, and it can be found in milk in the UK. It has an important biological function in that it is used to synthesize thyroid hormones that act on gene transcription in the process of regulating the basal metabolic rate. Some of the recommended amounts of iodine in food are as follows, given in micrograms (mcg): 1-3 years: 900 mcg, 4-8 years: 300 mcg, 9-13 years: 600 mcg, 17 years and older: 1100 mcg, pregnant/lactating women 14-18 years: both 900 mcg, pregnany/lactating women 19 years and older: both 1,100 mcg.
See Iodine deficiency, Metabolism