Who Found Vitamin B2, and Why a Yellow Pigment Became Science
Vitamin B2 began as a yellow-green glow in cow's milk. This history covers Blyth's 1870s milk pigment, Warburg's yellow enzyme, the 1937 name riboflavin, and the FAD step that links B2 to NAD.
The history of vitamin B2 starts with a glow in milk, not with a disease. Alexander Wynter Blyth, an English chemist, isolated a yellow-green fluorescent material from milk whey in the 1870s and named it lactochrome. It took until the early 1930s to identify that material as riboflavin, and the early work ran on rats, not patients. Isolating it was brutal. According to PubMed, a 2012 historical review by Northrop-Clewes and Thurnham ([DOI](https://doi.org/10.1159/000343111)) reports that Kuhn's group needed about 15,000 liters of milk, or the dried albumin from 34,000 eggs, to get one gram of what Kuhn called the "beautiful yellow substance." The same review says riboflavin deficiency has no clear associated disease and has never been fatal. ## A yellow enzyme turns a pigment into biochemistry In 1932, Otto Warburg and Walter Christian extracted a yellow enzyme from brewer's yeast. It linked the oxidation of glucose-6-phosphate to molecular oxygen, and dialysis stripped out both its color and its activity. Richard Kuhn, who stayed in close contact with Warburg, had found a breakdown product of the milk pigment called lumiflavin. He realized it was probably the yellow component of Warburg's enzyme, and he proposed that vitamin B2 was its precursor. Hugo Theorell purified this "old yellow enzyme" in 1935. In his 1955 Nobel lecture, he said its yellow cofactor was riboflavin 5'-phosphate, now called FMN. According to the review, that made the enzyme the first biochemical role for a vitamin. Kuhn's Nobel Prize in Chemistry (dated 1938, received 1939) cites his "work on carotenoids and vitamins" and does not name riboflavin ([NobelPrize.org](https://www.nobelprize.org/prizes/chemistry/1938/summary/)). ## What riboflavin does now The [NIH Office of Dietary Supplements](https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/) calls riboflavin an essential component of two coenzymes, FMN and FAD. It says both play major roles in energy production and cellular function. More than 90 percent of dietary riboflavin arrives as FAD or FMN. Our [mitochondrial health guide](/health/mitochondrial-health-complete-guide) covers the energy side in more detail. ## Named for its sugar, and mixed up with pellagra The pellagra confusion came first. In 1927, Joseph Goldberger thought his anti-pellagra factor was the same substance as vitamin B2. A 1935 study by Paul György, Thomas Birch and Leslie Harris showed the two were different. Elvehjem's group in Wisconsin later identified nicotinic acid as the pellagra-preventing part of the B2 complex. The name riboflavin arrived in 1937, when the American Medical Association's Council on Pharmacy and Chemistry adopted it. The active molecule carries ribose, a sugar. ## The first human proof came in 1939 According to the review, William Sebrell and Roy Butler reported in 1939 that 13 of 18 women on a riboflavin-poor diet developed reddened, cracked lesions at the lips and mouth corners. Daily synthetic riboflavin cleared them, and stopping it brought them back. The high-dose story came later, and the record is mixed. According to PubMed, Schoenen and colleagues ran a 1998 randomized trial in *Neurology* with 55 patients who had migraine. They gave 400 mg of riboflavin a day or placebo for three months. Riboflavin cut attack frequency more than placebo did, and 59 percent of the riboflavin group were responders (at least a 50 percent improvement), against 15 percent on placebo ([DOI](https://doi.org/10.1212/wnl.50.2.466)). A 2008 trial by MacLennan and colleagues gave 200 mg a day to 48 children. It found no significant difference from placebo and noted a high placebo response ([DOI](https://doi.org/10.1177/0883073808318053)). Both trials measured migraine attack frequency, and both are research findings, not dosing advice. ## Where NAD comes in Riboflavin is not part of NAD, but FAD sits on one step of a route to it. The NIH says the conversion of the amino acid tryptophan to niacin requires FAD. Our [NAD longevity guide](/health/nad-longevity-complete-guide) covers NAD itself, and our [research page on diet, tryptophan and niacin](/research/can-diet-raise-nad-tryptophan-niacin) asks whether food can raise it. ## Bottom line Treat riboflavin as a food nutrient with a well-documented history and a mixed record at high doses. The NIH lists an RDA of 1.3 mg a day for men and 1.1 mg for women, ages 19 to 50. Milk, egg white, leafy vegetables and whole grains are among the sources the review names. If you are weighing a high-dose product, the migraine evidence is one positive adult trial and one trial in children that found no benefit over placebo. ## Frequently asked questions ### Why was riboflavin first noticed as a yellow pigment? Because it glows. Blyth isolated a material from milk whey in the 1870s that fluoresced yellow-green in light, and he named it lactochrome. The 2012 review dates his observation to 1879 in its text and to 1872 in its abstract, so "the 1870s" is the defensible date. Blyth could not work out the chemistry. Light can also readily destroy riboflavin, according to the same review. ### How did yellow enzyme research lead to vitamin B2? Warburg and Christian reported a yellow enzyme from brewer's yeast in 1932. Richard Kuhn had found lumiflavin, a breakdown product of the milk pigment, and proposed that vitamin B2 was the precursor of the enzyme's yellow component. Theorell purified the old yellow enzyme in 1935. In his 1955 Nobel lecture, he identified its yellow cofactor as riboflavin 5'-phosphate, now called FMN. The 2012 review calls that the first biochemical role for a vitamin. ### Which coenzymes depend on riboflavin? Two: FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide). The NIH Office of Dietary Supplements calls riboflavin an essential component of both, and more than 90 percent of dietary riboflavin arrives as FAD or FMN. The NIH also says FAD is needed to convert tryptophan to niacin, and FMN is needed to convert vitamin B6 into the coenzyme pyridoxal 5'-phosphate. ### Which foods are the main sources of riboflavin? The 2012 review lists milk, leafy vegetables, whole grains, liver, egg white, cheese and fresh meat. The NIH says the main form in eggs and milk is free riboflavin, while most other foods carry it as FAD. The NIH lists an adult reference intake of 1.3 mg a day for men and 1.1 mg for women, ages 19 to 50. Ultraviolet rays and sunlight can readily destroy riboflavin, according to the review. ### What did the high-dose riboflavin studies test? Migraine attacks. According to PubMed, Schoenen and colleagues gave 55 patients 400 mg a day or placebo for three months in a 1998 trial, and riboflavin reduced attack frequency more than placebo did. MacLennan and colleagues gave 200 mg a day to 48 children in 2008 and found no significant difference from placebo. Both studies measured migraine attacks, and both are research findings, not a recommendation. ### How does riboflavin connect to the NAD story? Riboflavin is not part of NAD, but FAD sits on one step of a route to it. The NIH says converting tryptophan to niacin requires FAD. Our NAD longevity guide covers NAD itself. Our research page on diet, tryptophan and niacin asks whether food can raise NAD. Riboflavin status is one input to that chain, not a shortcut around it. ## Next reads - [Our NAD longevity guide](/health/nad-longevity-complete-guide) covers NAD itself. - [Who found vitamin B12](/blog/history/history-of-vitamin-b12-from-liver-cure-to-cobalamin) follows another vitamin whose treatment worked 22 years before anyone isolated the vitamin. ### Related reading - [the B-complex story, from one factor to eight](/blog/history/history-of-the-b-complex-from-one-factor-to-eight) - [the niacin story, from pellagra to flush](/blog/history/history-of-niacin-b3-from-pellagra-to-flush) - [the thiamine story, from beriberi to Eijkman](/blog/history/history-of-thiamine-b1-from-beriberi-to-eijkman)