Is There a Vitamin B4? The Story of a Missing Vitamin

Vitamin B4 did exist, at least on paper. In the late 1920s and early 1930s, researchers assigned the name to a substance they believed was essential for growth in rats, and that substance turned out to be adenine, one of the building blocks of DNA and RNA. The designation was eventually stripped because human cells manufacture adenine on their own, which disqualifies it from vitamin status under the working definition nutritional scientists use. The story of B4 is really the story of a naming system that ran ahead of the science, and the wreckage it left behind helps explain why the B vitamins jump from B3 to B5 to B6 with mysterious gaps in between.

How the B Vitamins Got Their Numbers

In the early twentieth century, researchers knew that certain foods contained trace substances necessary for health, but isolating and identifying those substances was painstaking work. What was originally called “vitamin B” turned out not to be a single compound but a whole family of them dissolved in water. As each new factor was separated from the mix, it received the next available number: B1, B2, B3, and so on. The problem was that different labs in different countries were often isolating the same compound independently and giving it different names, or naming something before confirming it was truly a distinct substance.

A 1938 review in JAMA acknowledged the confusion directly, noting that different terms had been applied to newly discovered factors and that “specific terms have been coined before the existence of separate entities has been definitely established.”¹ This was the root of the numbering mess. Some numbered entries turned out to be duplicates of compounds already catalogued under a different number. Others, like B4, were real compounds that simply failed to meet the evolving criteria for what counts as a vitamin. A comprehensive cataloguing effort later found that all 26 letters of the alphabet had at some point been used to name putative vitamins, resulting in at least 67 distinct alphabetical vitamin names across the scientific literature.² The simple alphabetical naming system proposed in 1920 lasted less than a decade before collapsing under its own contradictions.

The result is the patchwork we live with today. We have B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). The gaps where B4, B8, B10, B11, and others once sat are not accidents or oversights. They are tombstones for candidates that did not survive closer scrutiny.

What Adenine Actually Does

Calling adenine unimportant would be wildly wrong. It is one of the four nucleotide bases that make up DNA and RNA, which means every cell in your body depends on it for storing and reading genetic information. It is also a structural component of ATP, the molecule cells use as their primary energy currency, and of several coenzymes involved in metabolism. Without adenine, life as we know it does not function.

What makes adenine different from, say, vitamin C is that your cells are perfectly capable of building it from scratch. Humans have a complete biosynthetic pathway for purines, the chemical family adenine belongs to. Your liver, your gut lining, and other tissues can assemble adenine using small molecules already floating around in the body. Cells also recycle purines from old or damaged DNA and RNA through salvage pathways, which is metabolically cheaper than building them new. Research in mice has shown that both dietary purine intake and this internal manufacturing process work together to keep purine levels stable across tissues.³

So adenine is essential for life but not essential in your diet. That distinction is the whole ballgame.

Why Adenine Was Stripped of Its Vitamin Title

The definition of a vitamin has always been a moving target, but the core idea has remained fairly stable: a vitamin is an organic compound that your body needs for normal function, that you cannot produce in sufficient quantities internally, and that you must therefore obtain from food. If your body makes enough of something on its own, it is not a vitamin no matter how critical it is biologically. The contemporary discussion around vitamin definitions explicitly grapples with this boundary, incorporating the concept of conditional essentiality to distinguish classical vitamins from other bioactive substances that the body can synthesize.⁴

When B4 was first proposed in the late 1920s, researchers were studying growth factors in yeast and other organisms. A 1930 paper described methods for assaying vitamin B4 activity, and early work suggested that crystals with B4 activity might be related to adenine.⁵ A 1933 communication noted that the crystals isolated by researchers “were specifically stated by them to have vitamin B4 activity,” but no claim was made that those crystals were actually the pure vitamin itself. The identification was tentative. As biochemistry advanced and purine biosynthesis was mapped out in humans, it became clear that healthy people synthesize all the adenine they need. The B4 label quietly fell away.

The early researchers were not wrong that adenine mattered for growth in certain organisms and under certain experimental conditions. They were working with incomplete knowledge of mammalian biochemistry. In the 1920s and 1930s, the metabolic pathways for purine synthesis had not yet been fully characterized, so it was reasonable to suspect that adenine might need to come from food.

When Adenine Becomes a Problem

One reason adenine never needed to be classified as a vitamin is that getting too much of it is a far more realistic concern than getting too little. In animal studies, feeding mice a diet enriched with adenine causes a specific form of kidney disease. The excess adenine gets converted to 2,8-dihydroxyadenine, which forms crystals that deposit in the kidney tubules. This triggers a cascade of damage: tubular injury, inflammation, fibrosis, and progressive kidney disease.⁶

The kidney damage is not subtle. After just three weeks on an adenine-overloaded diet, mice show widespread crystal deposits in tubular spaces and in the tissue between tubules, along with granuloma formation, collagen buildup, and intense inflammatory activity.⁷ This adenine-overload model is now used routinely in labs to study chronic kidney disease. The irony is worth appreciating: the former “vitamin” is used as a toxin in experimental settings.

For humans eating a normal diet, adenine overload is not a practical worry. The amounts used in these animal models are far beyond anything a person would encounter from food. But the point stands that adenine is not something your body is short on, and supplementing it would be pointless at best and harmful at worst. If you see a supplement marketed as “vitamin B4,” treat that as a red flag about the seller’s credibility.

Your Gut Bacteria Make Purines Too

The case against adenine as a vitamin gets even stronger when you consider that your intestinal bacteria are pumping out purines on their own. Research has shown that the gut microbiota serves as a significant source of exogenous purines for the intestinal lining. These microbiota-sourced purines are taken up by the colonic tissue and used for nucleotide production and energy balance.⁸

This matters because it means your body has not one but two non-dietary sources of purines: its own biosynthetic machinery and the metabolic output of trillions of gut microbes. In germ-free mice (animals raised without any gut bacteria), colonic tissue that lacks these microbial purines shows signs of energy stress, impaired cell proliferation, and compromised mucus barrier integrity. When researchers reintroduced purine-producing bacteria or simply supplemented the purines directly, those deficits reversed.

So even if you theoretically ate a diet with zero purine content, your own cells and your gut flora would still be manufacturing adenine and its relatives. This is the opposite of the vitamin scenario, where removing a nutrient from the diet eventually causes deficiency symptoms that can only be fixed by adding it back.

Choline and the Vitamin Boundary

If adenine is the clearest example of something that was called a vitamin and then declassified, choline sits on the opposite side of the same blurry line. Choline was recognized as an essential nutrient by the Food and Nutrition Board in 1998, and roughly 90 percent of Americans fall below the adequate intake level for it.⁹ Humans can produce small amounts of choline internally through a liver enzyme pathway, but not enough to prevent deficiency. That internal production pathway is the only endogenous route mammals have for choline biosynthesis, and when it malfunctions, phospholipid metabolism falls out of balance.¹⁰

Choline is sometimes informally called vitamin B4 in popular nutrition writing, which adds to the confusion. It is not officially classified as a B vitamin by most authorities, but it shares metabolic pathways with folate and B12, and the case for calling it one is stronger than many people realize. The reason it remains in limbo is partly historical: by the time choline’s essentiality was firmly established in the 1990s, the B vitamin numbering system had long been frozen. Nobody was handing out new B numbers.

The choline story illustrates that the vitamin/non-vitamin distinction is not as clean as textbooks make it seem. The question is always “how much can your body make, and is it enough?” For adenine, the answer is clearly yes, so it lost its number. For choline, the answer is “some, but not nearly enough,” so it gained essential nutrient status without quite getting a formal B designation.

Other Ghosts in the B Vitamin Lineup

Adenine is far from the only casualty. The gaps in the B numbering system each have their own backstory. B8 was once assigned to inositol, a sugar alcohol that the body produces in adequate quantities. B10 and B11 were at various points linked to forms of folic acid or to growth factors in chick nutrition that turned out not to be distinct vitamins in humans. B13 was orotic acid, B15 was pangamic acid, and B17 was amygdalin (better known in its semi-synthetic form as laetrile, which was controversially promoted as a cancer treatment). None of these met the criteria for vitamin status in humans upon further investigation.

The pattern is remarkably consistent. Researchers working with animal models, especially rats, chicks, and insects, would identify a compound necessary for growth in that species. The compound would receive a B number. Then one of two things happened: either it turned out to be a compound already catalogued under a different name, or it turned out to be something humans can synthesize internally. In a few cases, the supposed vitamin was never convincingly isolated at all.

Why Some Species Need What Others Can Make

The reason these mix-ups happened so often is that vitamin requirements genuinely differ between species. A compound that is a true vitamin for one organism might be dispensable for another because of differences in their metabolic toolkits. The evolutionary explanation for this is fascinating: organisms lose the ability to synthesize a nutrient when they can reliably get it from their diet, because maintaining the genes for a biosynthetic pathway carries a metabolic cost.

Research on vitamin B6 biosynthesis across 122 species whose genomes have been fully sequenced illustrates this vividly. The study found that the genes responsible for B6 synthesis were lost independently multiple times across different animal lineages, with the breakdown of the biosynthetic pathway happening at least three times in animal evolution alone.¹¹ The order in which genes were lost was conserved across different evolutionary lineages, suggesting that the process follows a predictable pattern rather than happening randomly.

This dynamic explains why a compound like adenine can be a genuine growth requirement for yeast strains that have lost the relevant biosynthetic genes. Adenine-auxotrophic yeast (strains unable to make their own adenine) are commonly used in genetics research, and when their adenine supply runs out, they stop dividing.¹² For these organisms, adenine genuinely functions like a vitamin. Humans simply never lost the relevant genes, so for us it does not.

The Search for Undiscovered Vitamins

Given how messy the history has been, you might wonder whether new vitamins could still be discovered. The short answer is that it is unlikely but not impossible. Most candidate compounds that have been evaluated in recent decades have fallen short. Pyrroloquinoline quinone (PQQ), a compound found in many foods and present in animal tissues, generated excitement because it appeared to be essential for normal growth and development in mice.¹³ For a time, some researchers genuinely believed PQQ might earn a vitamin designation. But enthusiasm faded after it became clear that PQQ functions as a cofactor only in bacterial enzymes, not in mammalian ones, and its occurrence as a functional cofactor is restricted to bacteria.¹⁴

PQQ supplements are still widely sold, often with language that strongly implies vitamin status without technically claiming it. This is a recurring pattern in the supplement industry: compounds that were once vitamin candidates trade on their near-miss status for decades afterward. The regulatory framework for dietary supplements in the United States does not require proof that a substance is a vitamin before it can be sold, only that it is generally recognized as safe. So the marketplace is full of products labeled with abandoned B numbers and failed vitamin candidates, and the average consumer has no easy way to distinguish them from the genuine article.

The broader lesson from the B4 story is that the vitamin concept itself is less fixed than most people assume. What counts as a vitamin depends on the species, the individual’s genetics, the state of their gut microbiome, and how strictly you define “cannot synthesize enough.” The neat list of 13 vitamins taught in nutrition courses is a useful simplification, but the boundaries around that list have been debated for a century and remain the subject of ongoing scholarly discussion. Adenine’s brief tenure as B4 is just one chapter in that longer, messier, and more interesting history.