Why Is There No Vitamin F? How Vitamins Got Their Names and Why the Letters Skip

The video opens with a familiar memory: many people were made to eat Flintstones vitamins as children, and they tasted strange in a good way. Host Hank Green then asks what a vitamin actually is, and whether it is a specific thing or just a category for anything that is good for you.

He also raises several related questions: why there are so many B vitamins, why the letters jump from E to K, whether the vitamins share anything in common, and what makes them more special than the other things in food. To answer these, he says the story has to go back more than 100 years, to the early 1900s.

In the late 19th century, scientists began to realize that what we eat is as important as how much we eat. They became curious about why some foods are more nourishing than others. By then they knew about protein, fat and carbohydrates, which are now called macronutrients, as well as the importance of water and salt.

Still, it was clear that these five basics were not enough for good health. Diseases such as scurvy, in which people on long sea voyages lost their teeth and bled internally, and rickets, in which children's bones grew soft, weak and deformed, did not seem to be caused by germs. Germ theory was fairly new at the time, and scientists gradually concluded that some diseases must be related to food, not only in quantity but in quality.

In 1912, biochemist Frederick Gowland Hopkins published a series of experiments. When animals were fed mixtures of pure protein, fat, carbohydrate and salt, they did not simply fail to thrive; they could not grow at all. When small amounts of milk were added back into their diet, their health quickly improved and they could grow again.

In the same year, 1912, researcher Casimir Funk was investigating another disease, beriberi. Like scurvy and rickets, beriberi did not seem to be caused by infection, but it had serious consequences, including leg numbness and even heart failure.

Funk theorized that a substance combining 'vital' and 'amine' was missing from the food of people sick with beriberi, and he named it 'vitamine' because he thought it was an amine, an organic molecule made of carbon, nitrogen and hydrogen. The host says he was half right: something vital was missing from people's diets, something their bodies could not make and whose absence caused disease, but the substance that causes beriberi was not an amine.

Although the substance behind beriberi was not an amine, the name persisted as more vital compounds were discovered, and people began calling them vitamins. Funk also called them 'vitamines' because he was French, and the host reads that pronunciation aloud.

The host notes that researchers still debate the precise definition, but he gives one key distinction. To be a vitamin, a compound must be essential, meaning we need it to live and grow, but we cannot make it ourselves. It must also differ from the macronutrients, which the host says already do many other things. He adds that it is actually difficult to find compounds that fit this definition.

While the definition is complicated, the naming convention is simple: vitamins are named alphabetically in order of discovery, starting with Vitamin A.

Vitamin A was discovered in 1913 by two scientists, Marguerite Davis and Elmer McCollum. McCollum originally called the compound 'Fat-Soluble-A'. He was accused of scientific misconduct and of effectively taking other people's research, and the accusations became so serious that he left for a different university.

Decades later, archivists found evidence of data manipulation in McCollum's notebooks, so the host says it is possible he did some bad science in his career. Despite the drama around one of its discoverers, Vitamin A moved into the spotlight, and by the 1920s it was at the front of the vitamin list and people were beginning to understand what it does.

Vitamin A is a fat-soluble micronutrient that comes in many forms, one of the most common being retinol. It is found in high doses in animal products such as liver. Orange vegetables such as carrots contain beta-carotene, which the body converts into vitamin A.

A deficiency leads to eye lesions, which is why people have often been told that carrots are good for their eyes. The host adds that too much of a good thing is possible: too much vitamin A can cause birth defects, which is why eating liver, which has high vitamin A concentrations, is no longer advised during pregnancy.

The B vitamins were discovered between the 1920s and 1940s. There are so many because researchers initially thought all the B vitamins were the same thing. They were all essential nutrients that dissolve in water, and although researchers could tell they differed slightly chemically, they assumed the water-soluble compounds had essentially the same function in the body.

It is true that they all act as coenzymes, substances that bind to an enzyme to help it start working. Later, however, scientists realized that each B vitamin does something somewhat different, so the B complex was subdivided into numbers based on the order of discovery or isolation.

The host runs through the B vitamins. Vitamin B1 is thiamine, which cures beriberi and helps the body make energy from glucose. Vitamin B2 is riboflavin, which helps with vision and metabolism. Vitamin B3 is niacin, the compound Casimir Funk actually discovered; it supports digestion and the skin, and it does not cure beriberi. Vitamin B5 is pantothenic acid, which helps produce energy, and B6 is pyridoxine, which helps with blood oxygenation.

Vitamin B7 is biotin, which helps the body make fatty acids. Vitamin B9 is folate, or folic acid in synthetic form, which is essential for cell and tissue growth and is usually taken as a prenatal supplement. Vitamin B12 is cyanocobalamin, an essential nutrient for forming red blood cells.

Some numbered B vitamins were demoted. B4 turned out to be adenine, a component of DNA that the body makes all the time, so it is not a vitamin. B8 is inositol, which the body can use to help process insulin and also produces naturally, so it is not a vitamin either.

B10, or PABA, is part of the folic acid molecule, which is already Vitamin B9. B11 turned out to be salicylic acid, which is good for skincare and is a precursor to aspirin but is not exactly essential to health. The video also includes a sponsor segment for Uncommon Goods, which offers 15% off for viewers who visit the link given in the video.

Vitamin C was discovered in 1928. Like the B vitamins it is water-soluble, but it is different enough to stand on its own. Many animals can make vitamin C, also called ascorbic acid, but humans cannot. This matters because vitamin C is one of the building blocks of collagen, a structural protein that keeps bones, skin and ligaments healthy. A vitamin C deficiency therefore leads to scurvy, which is primarily caused by a lack of healthy collagen.

Vitamin C also acts as an antioxidant that protects the body from harmful free radicals, helps the body absorb iron and boosts the immune system. The host notes some controversy about the immune claim.

Vitamin C has been marketed for decades to fight colds and flu, but results from clinical trials have been mixed. The host says vitamin C does appear to shorten severe cold symptoms, so it could help when a person feels really ill, but it does not seem to do much for mild symptoms.

He warns against taking large amounts. Taking more than 1,000 to 2,000 mg of vitamin C in a day can lead to kidney stones and gastrointestinal problems.

The host adds that the body cannot store up vitamin C, which means there is no point in taking more than can be used in a given day. This follows the warning about kidney stones and gastrointestinal problems from high doses.

Rickets, which the host had asked about earlier, is caused by a deficiency of vitamin D. Vitamin D was identified between 1900 and 1920. Like vitamins A and B, it is a group of molecules, and D2 and D3 are the forms most important for human health, together called calciferol. Vitamin D helps the body process calcium, which is important for bone growth, and it also supports the immune system and helps with glucose metabolism.

Vitamin D is unusual because the body can make it when exposed to UV light: UVB rays convert a molecule naturally present in the body into the vitamin D it needs. Without UV light, the body will not make it. Because deficiency is real and can lead to rickets in extreme cases, scientists describe vitamin D as conditionally essential, meaning it can be made but only under the right circumstances.

Getting enough sun is not always easy, especially at high latitudes, and people now spend more time indoors. That is why babies are usually given vitamin D supplements from about the time they are born. The host clarifies that he is not recommending unprotected sun exposure: skin protected by sunscreen can still make vitamin D, and producing a small amount is probably not worth the long-term risk of skin cancer.

Like vitamin D, vitamin E was discovered in 1922. It is a group of eight fat-soluble molecules that differ slightly in chemical composition. Four are known as tocopherols and four as tocotrienols, but only alpha-tocopherol meets the body's requirements, so the term vitamin E usually refers to it.

People are very rarely deficient in vitamin E, so most people do not need to do anything special to maintain their levels. It is best known for helping keep skin and hair healthy, which explains why it appears in many hygiene and cosmetic products.

Vitamin K was discovered in the early 1930s. It is another family of fat-soluble molecules, including phylloquinone (K1), menaquinone (K2) and the synthetic K3, menadione. It helps with blood coagulation and bone mineralization by activating the proteins that make blood clot, which makes it especially important for newborns, who are born with very low levels. Newborns are therefore usually given vitamin K shots to lower the risk of dangerous internal bleeding. There is also some evidence that vitamin K might help with osteoporosis, though this remains an active area of research.

As for the missing letters, the host explains that the candidates did not meet the standard definition of a vitamin. Vitamin F turned out to be the fatty acids omega-3 and omega-6. Those are needed in the diet, but they are fats and therefore fall under macronutrients rather than vitamins. Vitamin G turned out to be vitamin B2, vitamin H was actually vitamin B7, vitamin I was never assigned for some reason, and vitamin J also turned out to be B2.

No new vitamins have been added to the list since about the 1940s. Instead, researchers have focused on refining their understanding of the vitamins already known. The host says discovering vitamins changed lives in important ways. Beyond treating conditions such as scurvy and rickets, knowledge of vitamins allowed food to be fortified so that populations get enough of these nutrients, which is why milk and cereals are often fortified.

The host also points to the value of a balanced diet with plenty of fresh fruit and vegetables, and says that when deficiencies occur, doctors know how to offer targeted treatments. He concludes that although the naming convention may not always make sense and the definitions may need updating, we owe much to the vitamins and the researchers who discovered them.