Why are vitamins labeled with letters?: Decoding the Alphabet of Nutrition

October 11, 2025 •

3 min read

Did you know that the term 'vitamin' was originally coined as 'vitamine' in 1912? The peculiar naming system we use today, answering why are vitamins labeled with letters?, is a fascinating story of scientific discovery, reclassification, and historical happenstance. The seemingly random alphabet soup is, in fact, a timeline of early nutritional science.

Quick Summary

Explains the historical context behind the alphabetical naming of vitamins, from early placeholder labels to the reclassification of compounds. It details the origin of the term 'vitamin,' the B-complex numbers, and the reasons for missing letters.

Key Points

Chronological Discovery: Vitamins were initially labeled with letters in the order they were discovered in the early 20th century.
Historical Reclassification: Many letters (like F, G, H) were later abandoned because the substances were reclassified as other vitamins (e.g., Vitamin G became B2) or found not to be essential for human health.
The B-Complex Breakdown: The B vitamin was initially thought to be a single entity but was later found to be a group of distinct water-soluble compounds, leading to the numbered system (B1, B2, etc.).
Non-Alphabetical Naming: Some vitamins, like Vitamin K, were named based on their function. 'K' comes from the German word 'Koagulation' (coagulation).
Simplified Labels vs. Chemical Names: While common letter names persist, scientists primarily use chemical names. The letters are a simplified shorthand for more complex molecules, a holdover from early nutritional science.
Missing B Numbers: Gaps in the B-complex numbering (e.g., no B4) exist because substances once thought to be vitamins were later removed from the list.

The Genesis of the Vitamin Alphabet

The letter-based naming of vitamins stems from early 20th-century nutritional discoveries. In 1912, Casimir Funk, while studying beriberi, isolated micronutrients and called them "vitamine," from "vital" and "amine." The 'e' was dropped in 1920. Elmer McCollum's rat experiments led to the identification of a fat-soluble "fat-soluble A" and a water-soluble "water-soluble B." As more factors were found, they were assigned subsequent letters.

The Chronological Alphabet and its Anomalies

Early letters followed discovery order. Vitamin A (1913) was McCollum's fat-soluble factor. Vitamin C is the anti-scurvy factor. Vitamin D, an anti-rickets factor, is fat-soluble. Vitamin E, found in 1922, is linked to fertility. However, this system wasn't strict; Vitamin K was named after the German word Koagulation (coagulation) by Henrik Dam in 1929, breaking the sequence.

The B-Complex Breakdown

The water-soluble "B" factor was initially considered one vitamin but was later found to be a complex of distinct compounds. This led to numbered subtypes, with B1 (thiamine) and B2 (riboflavin) among the first identified.

The Fate of the Missing B's

Gaps in B vitamin numbering (like B4 or B8) reflect the historical process of reclassification. Substances once thought to be B vitamins were either reclassified or deemed non-essential. For instance, Vitamin B4 was an early name for choline, now considered an essential nutrient but not a vitamin.

The Mystery of the Missing Letters

Letters like F, G, H, I, and J are missing because potential vitamins assigned these letters were later found not to be true vitamins or were reclassified. Vitamin F was essential fatty acids (now classified separately). Vitamin G became B2. Vitamin H is now Biotin (Vitamin B7). Vitamin I was never formally recognized. Vitamin J was also reclassified as a form of Vitamin B2.

Modern Nomenclature: Beyond the Alphabet

Scientific naming now favors chemical names (e.g., ascorbic acid for C) for precision. This shift occurred as chemical structures were determined. However, the letter names remain common for familiarity. The alphabetical names are simplified references to complex molecules.

The Vitamin Classifications at a Glance


Feature	Fat-Soluble Vitamins	Water-Soluble Vitamins
Members	Vitamin A, D, E, and K	B-Complex (B1, B2, B3, B5, B6, B7, B9, B12) and Vitamin C
Storage	Stored in the body's fatty tissue and liver. Can build up to toxic levels if over-consumed.	Cannot be stored in the body and must be consumed regularly. Any excess is excreted in urine.
Functions	Diverse roles, including vision (A), bone health (D), antioxidant properties (E), and blood clotting (K).	Crucial for cellular metabolism, energy production, red blood cell synthesis, and nerve function.
Risk of Deficiency	Deficiency can occur with inadequate intake, especially for those with fat absorption issues.	Deficiency is common due to frequent excretion, necessitating consistent dietary intake.

Conclusion

The alphabetical and numerical vitamin names are a historical reflection of early nutritional science. The system evolved through discovery and reclassification rather than a planned approach. The letter labels persist in common use due to familiarity. Understanding this history highlights the importance of a balanced nutrition diet. For more information, resources like the NCBI StatPearls series on vitamins are available.

Frequently Asked Questions

Letters like F, G, H, and I were once used for substances believed to be vitamins, but were later reclassified or deemed not essential. For example, Vitamin G is now known as Vitamin B2, and Vitamin F was reclassified as essential fatty acids.

The B vitamins were originally thought to be a single substance, but scientists later discovered it was a complex of several different compounds. They were then numbered sequentially (B1, B2, etc.) as the individual compounds were identified within the complex.

Vitamin K was named by Danish biochemist Henrik Dam for its role in blood clotting. He named it after the German word for coagulation, 'Koagulation,' which starts with 'K'.

No, the word 'vitamin' was coined by Casimir Funk in 1912. He originally called them 'vitamines' (vital amines), but the 'e' was dropped in 1920 when it was discovered not all of them contained amines.

No, the alphabetical naming system is an outdated practice from the early days of nutritional science. New essential nutrients are identified and classified using their chemical names.

Some numbers in the B-complex, like B4, are missing because the substances they represented were found to be either non-essential for humans or reclassified. The list was refined over time as scientific understanding improved.

The lettered vitamins are the most well-known, but there are other essential nutrients your body needs. These are typically referred to by their chemical names or categories, such as choline, which was once referred to as Vitamin B4.