Iodine was one of the earliest trace elements to be identified as essential. By 2700 BC, the Chinese treated goiter by feeding seaweed, marine animal preparations and burnt sponge (rich in iodine). 1 In the first half of the 19th century, the incidence of goiter was linked with low iodine content of food and drinking water. By the late 19th century, the geographic distribution of endemic goiter and cretinism was recognized to extend around the world. 2 In the 1920s, iodine was shown to be an integral component of the thyroid hormone thyroxine, required for normal growth and metabolism, and later in 1952 of triiodothyronine.