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

 

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

 

Brown seaweeds, acting as biological accumulators of iodine, contain 30,000 times more iodine than any other living organism. It has been suggested that iodine plays an important role in protecting 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 it is one reason this element is essential for animal development and the evolution of the human brain.

 

Iodine was first described by Courtois in 1811, when treating algae ash with sulfuric acid produced a purple vapor that condensed into dark purple crystals. Its name derives from the Greek iodes, meaning violet. In 1820, Dr. Jean-François Coindet was the first to use the newly discovered element, in the form of a solution of iodine and potassium iodide in alcohol (tincture of iodine), to treat an abnormal thyroid growth, known as goiter. Later, this same researcher observed 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, which contains iodine and is essential for normal mammalian development. For this reason, most research on iodine physiology in humans and animals has focused on its role as part of these hormones. However, in recent years, numerous investigations have revealed its ancestral antioxidant function in all the cells that take it up, from primitive algae to the most recent vertebrates. In fact, in its molecular form (I2), it binds to reactive oxygen species, inhibiting their oxidizing action and protecting cellular components from oxidation.