Why do some vitamins have names? The surprising history of their alphabetical titles

December 12, 2025 •

3 min read

In 1912, Polish biochemist Casimir Funk coined the term 'vitamine,' a combination of 'vital' and 'amine,' after his research on nutrients vital for health. This initial discovery began the process of assigning alphabetical labels, but it does not fully explain why do some vitamins have names while others are known by numbers or complex chemical titles.

Quick Summary

The alphabetical names of vitamins like A, C, and D trace back to their order of discovery, while the numbered B-complex vitamins arose from later chemical analysis. This inconsistent system reflects a century of scientific evolution, reclassification, and the process of isolating multiple compounds from what was initially believed to be a single entity. The result is a mix of simple letters, numbered sub-categories, and chemical identifiers.

Key Points

Chronological Discovery: Early vitamins were simply assigned letters in the order they were discovered, starting with 'fat-soluble A' and 'water-soluble B'.
The B-Complex: 'Vitamin B' was found to be a family of compounds, not a single one, leading to the numbered system (B1, B2, etc.) to differentiate them.
Missing Letters: Letters like F, G, and H were either reclassified (Vitamin G became B2) or found not to be essential vitamins, explaining the gaps in the alphabet.
German Origin for K: Vitamin K is an exception; it was named after the German word 'Koagulation' (coagulation) due to its role in blood clotting.
Chemical Names: As scientific knowledge grew, vitamins were also given chemical names based on their structure and function, like Ascorbic Acid (Vitamin C) and Cobalamin (Vitamin B12).

The Accidental Alphabet of Discovery

At the beginning of the 20th century, scientists began to understand that certain unknown substances in food were essential to prevent deficiency diseases like beriberi and scurvy. Rather than waiting to uncover the complex chemical structures, researchers simply assigned letters of the alphabet to these newly identified factors to categorize them. In 1913, American researcher Elmer McCollum categorized them by solubility: 'fat-soluble A' and 'water-soluble B'. As more were identified, the alphabetical naming continued, leading to vitamin C, vitamin D, and so on. This unsystematic, chronological approach is the primary reason for the seemingly random letters we use today.

The B-Complex Revelation and Numbered Confusion

One of the most complex parts of vitamin nomenclature history involves the B-complex. Originally, scientists believed there was only one 'water-soluble B' vitamin. However, further research revealed this was not a single entity, but a group of chemically distinct compounds that often occurred together in the same foods. To differentiate between these newly isolated members of the group, scientists began numbering them in the order of their discovery, giving rise to vitamin B1 (thiamine), B2 (riboflavin), and so forth. The B-complex is now understood to include eight different vitamins, each with its own number and chemical name.

The Fate of the Missing Letters

Curious observers often wonder why the vitamin alphabet skips from E to K, and why some B-numbers are missing. The reason is a combination of misclassification and refinement of scientific understanding.

Reclassification: Some substances initially designated with letters were later found to be other types of compounds. For example, what was once called vitamin G was reclassified as vitamin B2 (riboflavin) because of its chemical similarities to other B vitamins.
Disproven Factors: Other potential vitamins, such as the former vitamins F and J, were simply found not to be essential for human health and were discarded from the list.
Special Cases: The letter K was assigned to the vitamin involved in blood coagulation. Its name came from the German word 'Koagulation,' which starts with a 'K'. This happened at a time when most other letters were already taken or had been discarded.

Transition to Modern Chemical Naming

As biochemistry advanced, scientists moved away from the simple alphabetical system in favor of more precise chemical names based on a vitamin's structure and function. The letter-based names, however, persisted in common usage, creating the dual naming system we have today. The chemical names often provide clues about the vitamin's properties. For instance, Vitamin C is also known as ascorbic acid, with the name 'ascorbic' referencing its ability to prevent scurvy ('scorbutus'). Similarly, vitamin B12 is called cobalamin due to the cobalt ion at its center.

Comparison of Vitamins: Naming, Solubility, and Function


Vitamin	Common Name	Chemical Name	Solubility	Primary Function
A	Vitamin A	Retinol	Fat-soluble	Vision, immune function
B1	Thiamine	Thiamine	Water-soluble	Energy metabolism
B3	Niacin	Niacin	Water-soluble	Skin, nerve health
C	Ascorbic Acid	Ascorbic Acid	Water-soluble	Antioxidant, tissue repair
D	Vitamin D	Calciferol	Fat-soluble	Bone health, calcium absorption
E	Vitamin E	Tocopherol	Fat-soluble	Antioxidant
K	Vitamin K	Phylloquinone	Fat-soluble	Blood clotting

The Dual Naming System Explained

Understanding the vitamin naming system is best done by categorizing them by their solubility. Here is a list of the 13 essential vitamins:

Water-Soluble Vitamins

Thiamine (B1)
Riboflavin (B2)
Niacin (B3)
Pantothenic Acid (B5)
Pyridoxine (B6)
Biotin (B7)
Folic Acid (B9)
Cobalamin (B12)
Ascorbic Acid (C)

Fat-Soluble Vitamins

Vitamin A
Vitamin D
Vitamin E
Vitamin K

Conclusion: A Living History in a Name

The mixed and sometimes confusing system of vitamin naming is not the result of a single, neat classification, but a historical record of scientific discovery. The alphabetical names like A and C reflect the chronological order of their discovery, while the B-complex numbers demonstrate a deeper understanding that what was once considered a single substance was actually a group of related compounds. Ultimately, the names we use are a glimpse into the evolving scientific process, from initial observations of 'vital amines' to the detailed biochemical knowledge we possess today. For more information, you can explore detailed tables and classifications of these essential micronutrients learn more here.

Note: The historical classification and renaming of vitamins have been a gradual process informed by scientific advancements over decades, not a singular, orchestrated event.

Frequently Asked Questions

There is no Vitamin G or H because these were initially assigned to substances later reclassified as other vitamins or found not to be essential nutrients. For example, what was once called Vitamin G is now known as Vitamin B2, or riboflavin.

The letter name (e.g., Vitamin C) is a historical common name based on the order of its discovery, while the chemical name (e.g., ascorbic acid) is a precise scientific name based on its chemical structure and composition.

When scientists realized the original Vitamin B was a complex of several different compounds, they numbered the individual components (B1, B2, etc.) in the order they were isolated. Only the essential B vitamins in this complex were kept.

There are 13 essential vitamins for humans: A, C, D, E, K, and the eight B vitamins (B1, B2, B3, B5, B6, B7, B9, and B12).

No, the term Vitamin F was once used but is now considered an obsolete term for essential fatty acids (omega-3 and omega-6), which are not classified as vitamins.

Vitamin K was named by German scientists after the German word 'Koagulation' (coagulation), because the vitamin plays a crucial role in blood clotting.

While the 13 essential vitamins were all discovered by 1948, the alphabetical naming system is no longer used for new discoveries. Any new essential micronutrient would be identified by its scientific name rather than assigned a letter.