Erin Blakemore/ National Geographic:

Vitamin C to fight a cold? Carrots for vision-boosting vitamin A? Fatty fish—and sunlight—for bone-building vitamin D? We all know that vitamins are critical for our health, but how did they get their names and, more important, when were they found in the first place?
Before vitamins
Though humans have always understood there’s a connection between diet and health, it took thousands of years for modern nutrition research—bolstered by advances in chemistry, physics, and biology—to emerge.
Early nutrition experiments focused largely on the element nitrogen, first discovered in 1772, and whether its presence or absence in foods caused animals and humans to be healthy or sick. Then in 1838, Dutch chemist Gerardus Johannis Mulder proposed the existence of a compound he called protein, which he argued played a “principal role” in nourishment. For decades, historian Kenneth Carpenter writes, protein was considered the “true nutrient” for human health, despite emerging knowledge that fruits, vegetables, and milk eased conditions such as scurvy and rickets. While these afflictions were common among those with limited diets, researchers still blamed other factors, including infection, tainted food, or even sea air.
Diet deficiencies
Meanwhile, sailors on lengthy voyages had long been suffering from another ailment: beriberi, which can cause heart failure and a loss of sensation in the legs and feet.
Japanese naval physician Kanehiro Takaki had a pivotal theory: In the 1880s he noticed that poor people were likelier than their richer counterparts to develop the disease, and he suspected a lack of protein in their diets might play a role. Dutch army doctor Christian Eijkman conceived his own theory about beriberi after experiments with chickens.
The birds that ate the white rice common on Japanese naval vessels had similar symptoms. On the other hand, poultry who dined on brown rice provided by a cook who refused “to give ‘military rice’ to civilian chickens,” stayed healthy. Eijkman pursued that line of research and discovered that prison populations fed white rice were also afflicted with beriberi. Was the processed grain part of the problem?
‘Vitamines’ for health
Polish chemist Casimir Funk zeroed in on the hull and bran removed to make white rice and began his own experiments with pigeons in early 20th century. Pigeons fed only white rice became ill, but they improved when they ate rice bran and yeast. The discovery confirmed Takaki’s theory that diet and beriberi were linked, but the culprit wasn’t a lack of protein.
It was the lack of another substance, Funk theorized in 1912: a nitrogen-containing compound he called vitamine, a combination of the Latin word for “life” and “amine,” the name for a compound that contains nitrogen.
This discovery revolutionized scientific thought, suggesting that diseases might be caused by nutritional deficiencies—and cured by adequate amounts of the newly found compounds. “A monotonous diet ought to be avoided,” Funk declared.
Researchers rushed to isolate other micronutrients associated with afflictions such as rickets, scurvy, goiters, and more. Around the time Funk coined vitamine, American nutrition scientist Elmer McCullum conducted feed experiments with different animal populations and discovered that an “accessory” substance present in some fats was essential to rat growth. That fat-soluble substance became known as vitamin A.McCollum and others also conducted further experiments with Funk’s rice bran–derived nutrient, naming it vitamin B after beriberi. Eventually, it turned out that the substance was actually eight water-soluble vitamins, which were each given an individual name, such as thiamine, and numbered in order of discovery. The e in vitamine was dropped after scientists recognized that not all the compounds were nitrogen-containing amines. But the custom of naming vitamins alphabetically in order of discovery continued. Today four fat-soluble vitamins—A, D, E, and K—are considered essential to human growth and health.
So too are nine water-soluble vitamins: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), B12 (cobalamin), and C.
Vitamin…F?
One vitamin jumped ahead in the alphabet. Given its discovery date in 1929 by Danish researcher Carl Peter Henrik Dam, vitamin K likely would have been labeled with an earlier letter, such as F. But Dam’s research revealed that the substance was essential for blood coagulation—a word that starts with k in Scandinavian languages and German—and he proposed the new name instead.
It’s been decades since the last essential vitamin, B12, was discovered in 1948. Since then, researchers have focused on the health benefits of vitamins, learning more about the links between deficiencies and disease and using the substances to treat conditions such as pellagra and anemia. It appears unlikely that scientists will ever discover a new essential vitamin; all of our nutritional deficiencies seem to be accounted for.
But that doesn’t mean nutritional discovery has halted. In fact, this type of research is more advanced than ever, allowing scientists to delve into the secrets of even tiny traces of micronutrients that affect human health.
If the golden age of vitamin discovery was an appetizer of sorts, then scientists are hunkering down for the main course—a rapidly evolving understanding of the many ways food shapes our health and our lives, one microscopic substance at a time.