Who Named Vitamin P, and How Citrus Peel Led to the Flavonoid Story
Albert Szent-Györgyi's 1937 Nobel biography calls the vitamin nature of flavanone probable, not proven. The vitamin P name faded, but the flavonoids it pointed to became their own research field, where trials are small and mixed.
The history of vitamin P bioflavonoids is a story about a name that did not last. Albert Szent-Györgyi won the 1937 Nobel Prize for work on vitamin C, but his own Nobel biography also lists "the biological activity and probable vitamin nature of flavanone (vitamin P)." The name faded. The compounds it pointed to, the flavonoids, stayed in research. ## The Nobel was for vitamin C, not vitamin P The 1937 prize recognized work "with special reference to vitamin C and the catalysis of fumaric acid" ([Nobel Prize](https://www.nobelprize.org/prizes/medicine/1937/summary/)). The vitamin P idea sits in Szent-Györgyi's biography, which was written at the time of the award. There it appears beside his studies of biological oxidation and a flavin he called "cytoflav" ([Nobel biography](https://www.nobelprize.org/prizes/medicine/1937/szent-gyorgyi/biographical/)). The biography calls the vitamin nature of flavanone "probable," a hedge rather than a finding. ## Vitamin C and flavonoids are separate compounds The same biography describes a reducing substance he isolated from adrenals as one "now known as ascorbic acid." Flavonoids are a different group. NIH's vitamin C fact sheet lists "ascorbic acid with bioflavonoids" as one of several supplement forms of vitamin C, alongside sodium ascorbate, calcium ascorbate and other mineral ascorbates ([NIH ODS vitamin C](https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/)). Some products put the two side by side. [Good C](https://mtangelvitamins.com/products/good-c-120-caps-vitamin-c?utm_source=learn_hub&utm_medium=content&utm_campaign=blog_post&utm_content=history-of-vitamin-p-from-citrus-peel-to-flavonoids) lists 500 mg of vitamin C from calcium poly ascorbate, with 100 mg of citrus bioflavonoid complex, 50 mg of hesperidin and 50 mg of rutin in each capsule. The bottle holds 60 capsules, about $0.33 a day at one capsule daily, and the label directions read "one or more capsules daily, as a dietary supplement." ## What the capillary tests measure Capillary fragility describes how easily small blood vessels break under pressure. The Rumpel-Leede test is the clinical check that flags it. A [2024 dengue case report](https://doi.org/10.7759/cureus.72234) describes a positive Rumpel-Leede test as "indicating capillary fragility," and a [2022 report on the Rumpel-Leede phenomenon](https://doi.org/10.2147/CCID.S386426) describes "dermal capillary rupture caused by compressive forces." In that 2022 case, pneumatic compression on both legs produced non-blanchable purpuric macules that resolved when the compression stopped, and the authors hypothesized capillary fragility combined with increased intracapillary pressure as the mechanism. Both are case reports, so they explain the test without showing how well it predicts anything. ## Rutin, quercetin and the trial record A [2013 biographical article](https://doi.org/10.1016/j.clindermatol.2012.08.001) credits Szent-Györgyi with discovering "vitamin C and rutin (vitamin P)," which ties rutin to the vitamin P name. Quercetin is a separate flavonoid, covered on our [quercetin ingredient page](/ingredients/quercetin) and in our [quercetin and zinc article](/health/immune-health/quercetin-zinc-research). Results so far are small and mixed. A [2026 randomized trial](https://doi.org/10.1007/s11701-026-03816-5) enrolled 100 men after prostate surgery and tested an oral mix that included diosmin and hesperidin for one month. Lower-limb volume did not differ significantly between groups at one or three months. Genital pain at one month was lower in the treatment group, 2% versus 18% (p = 0.008). Persistent genital swelling at three months was absent in the treated group, compared with 8% of controls (p = 0.041), and lymphocele rates were similar. The authors call for larger studies with longer follow-up. NIH's vitamin C fact sheet also summarizes another study that found no differences in plasma vitamin C or urinary excretion among three forms, one of them ascorbic acid with bioflavonoids. **Bottom line.** Vitamin P was a probable vitamin that never became a settled one. The flavonoids it named went on to their own research record, and the trials we could verify are small or mixed. ## Frequently asked questions ### Why did Albert Szent-Györgyi call a citrus fraction vitamin P? His 1937 biography gives the name and calls the vitamin status of flavanone "probable," but it does not spell out his reasoning for the name. ### Why was vitamin P removed from the vitamin list? No formal removal decision is documented in the sources behind this page. The closest documented reason is the word "probable," which describes a vitamin status that was never proven. ### How are flavonoids different from vitamin C? Vitamin C is ascorbic acid, the reducing substance Szent-Györgyi isolated from adrenals. Flavonoids are separate compounds, which NIH lists alongside vitamin C in some supplement forms. ### What did the early capillary studies measure? The capillary tests measure capillary fragility, meaning how easily small vessels break under pressure. The Rumpel-Leede test is the clinical check that flags it, according to the 2022 and 2024 case reports linked above. ### Where do quercetin and rutin come from in the research? Rutin is the compound a 2013 biographical article ties to the vitamin P name. Quercetin is a separate flavonoid covered on our [quercetin ingredient page](/ingredients/quercetin). ### What do modern flavonoid trials actually show? So far, small and mixed. A 2026 randomized trial of an oral mix with diosmin and hesperidin found no significant difference in lower-limb volume and lower genital pain at one month. Another study summarized by NIH found no difference in plasma or urinary vitamin C among three forms, one with bioflavonoids. The biography that calls flavanone's vitamin status probable was written at the time of the award, so the hedge was on record in 1937. **Next reads** - [Our quercetin ingredient page](/ingredients/quercetin): the flavonoid covered in our ingredient monograph. - [The vitamin C history post](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid): the vitamin that stayed on the list, from scurvy to ascorbic acid. ### Related reading - [the vitamin P story](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid) - [vitamin P and the flavonoid story](/blog/history/history-of-the-b-complex-from-one-factor-to-eight) - [vitamin P and the flavonoid story](/blog/history/history-of-the-word-vitamin-from-vitamine-to-the-dropped-e)