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Everything Everywhere Daily: History, Science, Geography & More
The Element Iodine: Its Discovery, Health Benefits, and Why It’s in Salt
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The element iodine is far more important than you might think. It was discovered accidentally, yet it can be found almost anywhere. It's something so small you only need a trace amount of it, yet without it, entire populations can suffer devastating health consequences. It's been used as a medicine and a disinfectant, and it's even a critical chemical in the production of many of the electronic devices that we use today. Learn more about iodine and why this element matters so much on this episode of Everything Everywhere Daily. This episode is sponsored by Audible. It's time to believe in the Hail Mary, one of the most talked about science fiction adventures of the decade. Project Hail Mary by Andy Weir is now on the big screen, and there's never been a better moment to experience the audiobook that started it all. Ryland Grace is humanity's last hope. 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Iodine might seem like a rather odd element to be doing an episode on, but as you'll soon see, if it wasn't for iodine, you. You and I wouldn't be here. The story of iodine begins in 1811 in Paris, during the Napoleonic wars, in the workshop of a saltpeter manufacturer named Bernard Courtois. Saltpeter, or potassium nitrate, was essential for making gunpowder, and France needed enormous quantities of it to fuel Napoleon's military campaigns. Courtois produced saltpeter by extracting it from seaweed ash collected along the Brittany coast. One day, while cleaning his copper vats with sulfuric acid, he added too much acid and noticed something remarkable. A cloud of violet vapor rose from the mixture and condensed on cooler surfaces as dark, metallic looking crystals. Courtois was struck by the novelty of the substance, but lacked the resources to investigate it fully. He shared samples with colleagues and a few chemists, and within two years, the great French chemistry Joseph Louis Gay Lussac and the English chemist Humphry Davy had each independently confirmed that this violet colored substance was a new element. Gay Lussac named it Iodae, from the Greek word iodes, meaning violet colored, and the English adapted this to iodine. Iodine is the 61st most abundant element in the Earth's crust, making it relatively rare compared to many other elements, but not extremely rare. It belongs to the halogen group, the same chemical family as fluorine, chlorine and bromine, and shares their tendency to form ionic salts and readily reacts with other substances. In nature, iodine does not appear in its pure elemental form. Instead, it's almost always found as iodine ions chemically bonded to other elements. The oceans are the largest reservoir of iodine on Earth. Over billions of years, rainwater has slowly leached iodine from inland rocks and soils, carrying it through rivers and streams into the sea. As a result, seawater contains a modest but consistent concentration of iodine. And marine organisms. Seaweeds, fish, shellfish and sea vegetables have evolved to concentrate iodine in their tissues at levels far higher than the surrounding water. This is precisely why Bernard Courtois was able to extract so much iodine from seaweed ash in the first place. The distribution of iodine on land, however, is very uneven. Coastal regions and floodplains that receive regular deposits of marine sediment tend to have iodine rich soils, while mountainous inland areas, particularly those shaped by ancient glaciers which stripped away the topsoil, are severely iodine deficient. The Himalayas, the Alps, the Andes and the Great Lakes region of North America all are areas where iodine poor soil yields iodine, poor crops and livestock. This geographic imbalance has had enormous consequences for human health throughout history. More on that in a bit Concentrated deposits of iodine compounds are only found in a handful of places around the world. Chile is by far the largest producer of iodine, thanks to vast deposits of caliche ore in the Atacama Desert, which contain iodate minerals. Japan and the United States are also significant producers, obtaining iodine from ancient seawater trapped in rock formations, which are pumped to the surface and processed. These three countries together account for the overwhelming majority of the world's iodine supply. Iodine and its compounds have found their way into a surprisingly wide range of industrial applications in the chemical industry. Iodine serves as a catalyst in the production of a host of everyday plastics and synthesized fibers. Iodine compounds are used in the production of certain pharmaceuticals, dyes and specialty chemicals. One of the most important uses of iodine is the manufacture of polarizing films for liquid crystal displays. The thin layers in LCD screens used in televisions, computer monitors and smartphones all rely on iodine treated polyvinyl alcohol films to control light polarization. As global demand for flat panel displays exploded over the last several decades, this application became one of the dominant drivers of iodine consumption worldwide. Iodine also plays a critical role in animal feed supplements. Livestock raised far from sea are vulnerable to the same iodine deficiencies as humans, and the agriculture industry adds iodine compounds to feeds to ensure the health and productivity of cattle, pigs and poultry. Photography once relied heavily on silver iodine, a light sensitive material, though the digital revolution has dramatically reduced demand for it. Iodine is also used in the manufacture of certain inks, colorants and as a stabilizing agent in some industrial processes. One of the most widely known uses of iodine outside of medicine is as an antiseptic and disinfectant, and understanding why it works in this capacity of also helps explains why it can be toxic in large amounts. Elemental iodine and its compounds are powerfully reactive, as are all halogen elements on the periodic table. When iodine contacts a microorganism, it penetrates the cell and disrupts the organism's internal chemistry, particularly attacking proteins, nucleic acids and fatty acids in the cell membrane. This broad non selective chemical aggression is what makes iodine such an effective killer of bacteria, the viruses, fungi and protozoa. Tincture of iodine, which is iodine dissolved in alcohol, was one of the earliest antiseptics used in surgery and wound care. Its use became widespread in the later half of the 19th century as the germ theory of disease took hold. Providone iodine, a modern formulation that slowly releases iodine and is less irritating to tissue, remains a standard surgical scrub and wound antiseptic. Used in hospitals around the world today, iodine tablets are also used to purify drinking water in wilderness survival situations or humanitarian emergencies, killing pathogens reliably, even in cloudy or cold water. But now we get to the ultimate paradox of iodine. Iodine is a disinfectant that kills cells that it comes in contact with. Yet this same substance is also vital for human life. The human body contains only 15-20mg of iodine in total. But that tiny amount performs a function of outsized importance. It is the essential ingredient in the production of thyroid hormones. The thyroid gland, a butterfly shaped organ at the base of the throat, produces two primary thyroxine and triiodothyronine, which regulates metabolism throughout the body. These hormones govern the rate at which cells consume energy, influence heart rate and body temperature, regulate the creation of proteins, and are critically involved in the development and function of the brain and nervous system. Iodine is a structural component for both hormones. In fact, the numbers in their names refer directly to the number of iodine atoms in each molecule. Without adequate dietary iodine, the thyroid cannot produce sufficient hormones, which with serious and widespread consequences. The most obvious outward sign of iodine deficiency is goiter, an abnormal enlargement of the thyroid gland. When the body does not receive enough iodine, the thyroid gland cannot synthesize sufficient thyroid hormones. The pituitary gland, sensing this shortage, responds by releasing increasing amounts of thyroid stimulating hormone to push the thyroid to work harder. Under this constant hormonal pressure, the thyroid tissue proliferates and the gland grows larger and larger, sometimes to an extraordinary and visually dramatic degree. A severe goiter can reach the size of a grapefruit or even larger, creating a visible bulge on the front of the neck that's not merely cosmetic, but can cause difficulty swallowing, breathing and speaking. Goitres were historically common in inland mountainous regions throughout the world. In parts of the Alps, the Andes, and Central Africa, goitres were so common that they were simply considered a normal part of life. Some historians have speculated that the swollen necks depicted in certain medieval and Renaissance artworks reflect this widespread condition. In the 19th century, before the cause was understood, goitre was sometimes called Derbyshire Neck in England, Himalayan disease or mountain sickness, reflecting its geographic clustering in iodine poor upland regions. But goiter is only the most visible sign of iodine deficiency. The broader consequences are perhaps even more serious in pregnant women. Iodine deficiency impairs the neurological development of the fetus, leading to a form of intellectual disability known historically as cretinism, a term now replaced by the more clinical phrase iodine deficiency disorder. Children born to severely iodine deficient mothers may have stunted growth, deafness, and significant cognitive impairment. Even mild to moderate iodine deficiency in children has been linked to lower IQ scores and reduced school performance. The World Health Organization has identified iodine deficiency as the leading preventable cause of intellectual disability in the world. The recognition that goiter was caused by iodine deficiency, a connection that became firmly established in the early 20th century, led to one of the most successful public health campaigns in human history, the iodization of table salt. The idea was straightforward and rather elegant. Salt is consumed by virtually everyone in roughly predictable daily amounts. It's produced at a small number of centralized facilities, making it easy to fortify uniformly. And it's cheap. By adding a tiny quantity of potassium iodine or potassium iodate to table salt, governments could ensure that even people living far from the sea in iodine poor regions would receive enough iodine through their ordinary diet. Switzerland was among the first countries to introduce iodized salt on a national scale, beginning in 1922, after surveys revealed that goiter and cretinism were rampant in the alpine cantons. The results were dramatic. Rates of goiter fell precipitously within a single generation. The United states followed in 1924, and over the subsequent decades, country after country adopted salt iodization programs. Today, the World Health Organization estimates that approximately 88% of the world's population has access to iodized salt, and global levels of iodine deficiency disorder have been substantially reduced, although they've not been totally eliminated. Populations in parts of Sub Saharan Africa and South Asia, as well as some isolated rural communities, still remain at risk. It's worth noting that not all salt is iodized. Sea salt, kosher salt, and many artisanal salts sold in the United States and elsewhere do not contain added iodine. As consumer interest in specialty salts has grown and people have moved away from standard table salt, some nutritionists have expressed concern that iodine intake may be declining in certain populations. The apparent paradox of iodine, that being how can the same substance be a vital nutrient, a powerful germ killer, and a potential poison can all be explained by the foundational principle of the dose makes the poison Nearly every substance known to science is harmful at some dose and beneficial or neutral at lower doses. Water, oxygen, and vitamins A and D can all be lethal in large enough amounts in the bloodstream and thyroid gland, Iodine exists primarily as iodine ions, a relatively mild, chemically stable form that the body actively transports, stores, and incorporates into hormone molecules in tightly regulated amounts. The body requires only about 150 micrograms of iodine per day for an adult, an amount so small that it would be virtually invisible to the naked eye. Elemental iodine, the dark crystalline form, is a different matter. In this form, iodine is highly reactive. When applied to a wound or a contaminated water supply, that reactivity is an asset. It kills pathogens indiscriminately and quickly. But when ingested in significant quantities, elemental iodine exerts that same chemical effect on the tissues of the human body. It can irritate and burn the mouth, throat, esophagus, and stomach. Iodine is a reminder that some of the most important things in our lives are the ones we never notice. Iodine is invisible in our food, required only in the tiniest amounts. Yet its absence can affect entire populations, and its presence in fortified table salt has quietly improved the health of millions of people. It's proof that sometimes the smallest things can have the biggest impact the Executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Otkin and Cameron Kieffer. I have a small correction that many of you pointed out in the previous episode on the decision to drop the atomic bomb. I erroneously said that the bomb was used in Hiroshima on January 6th, when it was obviously August 6th. August was clearly in the script and I have no idea how January came out of my mouth, but it did. Today's review comes from listener Jack3P from Apple Podcasts in the United Kingdom. Greetings from the original Washington. After months of binging, I've finally listened to every single episode and can proudly say I've joined the Completionist Club. I might even be the first listener from Washington, England. The original Washington where George Washington's ancestors came from. Gary has a unique way of making every topic, whether it's obscure history, random facts or global events, accessible and genuinely entertaining. No filler, no nonsense, just great storytelling and bite sized episodes that leave you smarter every day. If you're on the fence about subscribing, don't be. This is hands down the best daily podcast out there. Thanks Gary for the effort you put into the show and keep them coming from across the pond. You've got a loyal fan in the uk. Cheers Jack. Thanks Jack. I'm always glad to see more members of the Completionist Club from across the pond. Please make sure to check out the Pan Hegarty and Newcastle Brown Ale available at your local clubhouse. Remember, if you leave a review on any of the major podcast apps, you too can have it right on the show.