Iodine is a chemical element belonging to halogens (group 17). It has as symbol I, with atomic mass 126.9 and atomic number 53. It is a component of the "nuclear ash" that formed our universe. In fact, it is derived from a nucleosynthesis process that occurred more than 10 billion years ago in a stellar supernova that exploded and dispersed its dust giving rise to the formation of our planet Earth about 5 billion years ago.


Iodine is essential in the diet of all living animals, so it is considered a trace element. Iodine is scarce on the surface of the earth, because, for hundreds of millions of years, it has been swept away by rain and glaciations, and transported from the earth's crust to the sea, which is enriched in form of iodide (I-). Seawater has approximately 60 micrograms per liter, while fresh terrestrial waters (estuaries, rivers, lakes) contain amounts of 10 to 200 times less.


Brown seaweeds, acting as a biological accumulator of iodine, contain 30,000 times more iodine than any other living being. It has been suggested that iodine played an important role in the protection of cellular components such as cell membrane lipids. Iodine is considered the first natural antioxidant used by living organisms to counteract the harmful effects of oxygen and is one of the reasons why this element is essential in animal development and in the evolution of the human brain.


Iodine was first described by Courtois in 1811 after algae ashes treated with sulfuric acid produced a purple vapor that condensed into dark purple crystals. Its name comes from the Greek iodes which means violet. In 1820, Dr. Jean-Francois Coindet was the first doctor to use the newly discovered element, in the form of a solution of iodine and potassium iodide in alcohol (tincture of iodine), to treat the abnormal thyroid growth so-called goiter. Later this same researcher observes that this combination of iodine in water (Lugol's solution) is an excellent antiseptic and disinfectant.


One hundred years later, in 1927 Sir Charles Harrington described the main thyroid hormone; Thyroxine contained iodine and that is essential for normal mammalian development. For this reason, most research on iodine physiology in humans and animals has focused on their role as part of these hormones. However, in recent years numerous investigations have found their ancestral antioxidant function in all the cells that capture it, from primitive algae to the most recent vertebrates. In fact, in its molecular form (I2) it binds to reactive oxygen species inhibiting its oxidizing action and protecting cellular components from oxidation.