Vitamins are organic compounds required in small quantities for normal metabolic function. Since the body cannot synthesize them quickly enough, these substances must generally be obtained from the diet. The familiar alphabetical system, such as Vitamin A or C, reflects the historical, laboratory-based process of their discovery. This simple letter designation served as a practical placeholder before the complex chemical structures of these compounds were fully understood.
The Initial Discovery and Alphabetical Order
The concept of vitamins began in the early 20th century with Polish chemist Casimir Funk, who coined the term “vitamine” in 1912. Funk theorized that “accessory food factors” were necessary to prevent diseases like beriberi and scurvy, initially believing these compounds were all nitrogen-containing amines. The “e” was later dropped when scientists realized not all substances contained an amine group.
The alphabetical naming convention was established by American biochemist Elmer McCollum and his colleagues in the 1910s. They separated the unknown substances into two fractions based on solubility. The compound found in butterfat was labeled “fat-soluble A,” and the factor found in rice bran and yeast was designated “water-soluble B.”
This simple A and B designation was used as a chronological label. Researchers continued this sequential labeling, assigning the next available letter to a newly isolated essential nutrient. This approach was purely a matter of convenience, providing a simple temporary name until the compound’s structure could be identified.
Understanding the B-Complex Family
The original “water-soluble B” fraction was quickly found to be far more complex than a single substance, which is why there is no single Vitamin B. As scientists purified and isolated distinct compounds from this fraction, they assigned numerical suffixes to keep them grouped under the “B” umbrella. This process explains the existence of multiple B vitamins, such as B1, B2, B3, and so on.
The numbering reflects the chronological order in which these individual substances were purified and their unique properties identified. For instance, Thiamine was the first component isolated and named B1, while Riboflavin was the next to be identified, becoming B2. Today, the B-complex includes eight chemically distinct vitamins, all of which function as coenzymes in cellular metabolism.
These numbered B vitamins, including Niacin (B3), Pyridoxine (B6), and Cobalamin (B12), are chemically unrelated to each other despite sharing the letter B. The common letter simply denotes their shared origin in the water-soluble fraction of early nutritional experiments. The numbering system was a necessary evolution to manage the complexity discovered within the single compound initially labeled “Vitamin B.”
The Letters That Vanished
The alphabetical sequence is notably incomplete, with letters like F, G, H, I, and J absent from the current list of recognized vitamins. These gaps exist because many substances initially given a letter designation were later reclassified and removed from the official vitamin list. Researchers initially assigned a letter to any factor that cured a specific deficiency disease in an animal model.
However, subsequent research often revealed that these substances were either duplicates of existing vitamins or were not truly essential micronutrients for humans. For example, the substance initially called Vitamin G was later found to be identical to Riboflavin, which was already established as Vitamin B2. Vitamin H was eventually reclassified and renamed Biotin, now considered one of the B-complex vitamins (B7).
In other cases, like the substance briefly called Vitamin F, the factor was reclassified as essential fatty acids, which are large molecules. The alphabetical sequence was pruned over time as scientific understanding matured. An exception to the sequential rule is Vitamin K, which was named after the German word Koagulation (coagulation), reflecting its role in blood clotting.
Modern Chemical Classification
While the letter names persist, scientists primarily classify vitamins based on their chemical properties, specifically solubility. This system divides them into two main groups: fat-soluble and water-soluble vitamins.
The fat-soluble group includes Vitamins A, D, E, and K, which are absorbed with dietary fat. They can be stored in the body’s fatty tissues and liver for extended periods.
The water-soluble group consists of Vitamin C and the entire B-complex family. These compounds are easily absorbed directly into the bloodstream and are not stored for long periods, meaning they must be consumed more regularly. The chemical names, such as Ascorbic Acid for Vitamin C or Retinol for Vitamin A, are now the preferred nomenclature in scientific literature.
The continued use of letter names is mainly a legacy of the historical discovery process, providing a familiar shorthand for the general public. The modern classification by solubility offers a more practical framework for understanding how the body absorbs, utilizes, and stores these compounds.