Lugol's solution is a mixture of elemental iodine and potassium iodide

People who work with diagnostic procedures have long been familiar with Lugol's solution. But the iodine-potassium iodide mixture has also been used to combat infections since the middle of the 19th century. How exactly does the iodine contained in it work and what are the current findings on its effectiveness in medicine and in the human body? 

Historical Background
Iodine (often spelled "iodine") got its name from the efforts of the French saltpeter maker Bernhard Courtois to produce gunpowder using seaweed. In his experiments, violet vapor developed - boiling iodine. In Greek, violet means "iodos", which is what the visible element was called from then on. Further research into iodine was carried out in 1814 by Nicolas Clément and Joseph Louis Gay-Lussac. However, its medicinal properties were already known in 1500 BC - people with goiter diseases, for example, were treated using the thyroid glands of sheep in order to provide them with sufficient iodine. The development of Lugol's solution goes back to the French doctor Jean Guillaume Lugol. In 1835, he produced a mixture containing iodine and potassium iodide in a mass ratio of 1:2, dissolved in water. The solution is reddish-brown in color, while its characteristic smell and taste are usually perceived as very unpleasant. Even in Lugol's time, his solution was used as a disinfectant, but also to detect starch. 

Iodine in Nature
Halogen is found in nature in a bound form and is found primarily in soil and rocks. In addition, there are deposits of sodium nitrate in hardened remains of bird droppings, particularly in Chile, which contain up to 1% iodine. Iodine often does not occur as a single element, but is found in compounds such as sodium iodate (NaIO3), lautarite (Ca(IO3)2) or sodium periodate (NaIO4). Seawater and seaweed also contain iodine. 

The element is also found in every cell in our body - it is therefore an essential micronutrient. The high iodine content in seafood supports a hypothesis put forward by evolutionary biologists: the consumption of these creatures in early human history played an important role in the development of the human brain and thus in evolution. The disinfecting properties against bacteria, viruses, fungi and parasites make the element particularly interesting. 

The Role of Iodine in Modern Nutrition
Iodine deficiency is a common diagnosis when it comes to thyroid problems such as goiter. Since the body cannot produce iodine itself, it must be supplied in sufficient quantities through food. It is particularly important for the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are needed for many aspects of our metabolism. A deficiency causes many symptoms of metabolic, muscle and nerve disease. The greatest need is in adolescents and adults up to the age of 50, with 200 micrograms of iodine per day. 
In order to function optimally, all of the body's glands depend on adequate amounts of iodine. These include the adrenal glands, the thymus gland, the ovaries, as well as the hypothalamus and the pituitary axis. An iodine deficiency therefore affects the entire hormonal system. In fact, after the thyroid gland, the ovaries have the second highest concentration of iodine in the entire body. 

Natural iodine supply is not actually a problem with a healthy diet. However, some people may be undersupplied, for example if they avoid salt or seafood for taste reasons or because of misinformation. For example, salt is still portrayed by some sources as bad for heart health. Today, many foods such as bread and pasta are also added with bromide and other additives that displace iodine. Modern agriculture is also now leading to a large-scale iodine deficiency in the soil, which ultimately becomes noticeable in grain. 
According to Dr. David Brownstein, author of the book “Iodine why you need it and why we cannot life without it”, a large number of people suffer from iodine deficiency. Lynne Farrow, author of the book “The Iodine Crisis”, also emphasizes that iodine deficiency has been prevalent in large parts of the population for several thousand years. The official figures from the WHO state that up to 72% of the world's population is probably affected by a preventable iodine deficiency disease. 
Regular consumption of iodine-rich foods should prevent deficiency symptoms. These include milk and dairy products, seafood, seaweed, algae, sea fish and iodized table salt. 

Iodine in Medicine
Iodine has long been used in cancer diagnostics in the form of Lugol's solution. In the so-called iodine test, it serves as a dye to make cell and tissue structures visible under the microscope, for example in mucous membrane samples. The background: healthy mucous membrane cells produce more glycogen (animal starch) than cancer cells. Due to the rapid storage of iodine in the glycogen molecules, healthy mucous membrane cells turn brownish, while cancer cells are whitish in color and can be distinguished from their healthy surroundings. The conspicuous white cell groups can be further analyzed after a biopsy. (Diagnostic efficiency of toluidine blue with Lugol's iodine in oral premalignant and malignant lesions. (Nagaraju et al.)) 

Other diagnostic applications of Lugol's solution can be found in microbiology for Gram staining of bacteria; in iodometry, an analysis method for various substances based on the reduction of iodine; or in the detection of alkaloids or chitin. 

But the well-known solution also plays a role for private individuals: it is an excellent disinfectant for throat infections. A few drops are dissolved in a little water and gargled without swallowing the solution. This can kill existing bacteria, for example, without the use of aggressive antibiotics. The iodine reacts with certain surface structures of pathogens, causing them to become inactive and die.