Vitamin P

Vitamin P is a historical term used to describe a group of plant-derived compounds collectively known as flavonoids, which are polyphenolic substances found in fruits, vegetables, teas, and other plant products. Although not officially classified as vitamins, these compounds were initially believed to possess vitamin-like properties that contributed to capillary strength and vascular health. The name “vitamin P” originates from the word permeability, reflecting early observations that these substances reduced capillary fragility and permeability.

Historical Background

The concept of vitamin P emerged in the 1930s when Hungarian scientist Albert Szent-Györgyi, who had already discovered vitamin C, observed that certain citrus extracts enhanced the effects of ascorbic acid in preventing bleeding disorders such as scurvy. He identified a compound in the white rind of citrus fruits that appeared to strengthen capillary walls and reduce permeability, and he called it “vitamin P.” Later research revealed that these effects were not due to a single chemical but to a family of related compounds now known as flavonoids.
Over time, the term “vitamin P” fell out of formal nutritional classification because flavonoids do not meet the biochemical definition of a vitamin — they are not essential for life in the strict sense, as deficiency does not cause a specific disease. Nonetheless, their physiological and pharmacological roles in human health remain significant.

Chemical Nature and Classification

Flavonoids, the substances once referred to as vitamin P, are polyphenolic compounds characterised by a basic C₆–C₃–C₆ carbon skeleton, comprising two aromatic rings connected by a three-carbon bridge. They occur widely in the plant kingdom and contribute to the pigmentation, flavour, and defence mechanisms of plants.
Flavonoids are classified into several subgroups based on their chemical structure:

• Flavones (e.g., luteolin, apigenin)
• Flavonols (e.g., quercetin, kaempferol, myricetin)
• Flavanones (e.g., hesperidin, naringin, eriocitrin)
• Flavanols (catechins) (e.g., epicatechin, epigallocatechin gallate)
• Anthocyanidins (responsible for red, blue, and purple plant colours)
• Isoflavones (e.g., genistein, daidzein, found mainly in soybeans)

Among these, rutin and hesperidin were originally isolated as the key compounds representing “vitamin P” due to their vascular effects.

Natural Sources

Flavonoids are widely distributed in plant-based foods and beverages. Common dietary sources include:

• Citrus fruits: oranges, lemons, and grapefruits (rich in hesperidin and naringin)
• Berries: blueberries, blackcurrants, and strawberries (rich in anthocyanins)
• Tea: both green and black teas (rich in catechins and theaflavins)
• Apples, onions, and kale: high in quercetin
• Red wine and cocoa: contain various flavanols and polyphenols
• Soy products: abundant in isoflavones

Regular consumption of these foods contributes to the dietary intake of vitamin P compounds, which may support overall vascular and metabolic health.

Biological and Physiological Functions

Although not a true vitamin, vitamin P (flavonoids) plays several important roles in maintaining physiological health:

• Capillary Strength and Permeability: Flavonoids help maintain the integrity of capillary walls by reducing permeability and fragility. This was the original observation leading to the term “vitamin P.”
• Antioxidant Activity: These compounds possess strong antioxidant properties, neutralising reactive oxygen species (ROS) and protecting cellular structures from oxidative damage.
• Anti-inflammatory Action: Flavonoids inhibit the production of pro-inflammatory mediators, helping to reduce tissue inflammation and contributing to cardiovascular protection.
• Cardiovascular Protection: Flavonoids enhance endothelial function, promote vasodilation through nitric oxide pathways, and help reduce blood pressure and cholesterol levels.
• Immune Support: By modulating immune responses and enhancing the action of vitamin C, flavonoids contribute to the body’s defence mechanisms against infection and stress.
• Antiviral and Anticancer Properties: Some flavonoids exhibit antiviral activity and have been studied for their potential in preventing or slowing the progression of certain cancers due to their ability to inhibit cell proliferation and induce apoptosis.

Relationship with Vitamin C

One of the most notable features of vitamin P compounds is their synergistic interaction with vitamin C (ascorbic acid). Early studies demonstrated that flavonoids help stabilise vitamin C, enhance its absorption, and prolong its antioxidant effects. Together, they contribute to the maintenance of healthy connective tissues, gums, and blood vessels. This interaction remains a focus of nutritional science, as combined intake of vitamin C and flavonoids has been shown to produce greater vascular and immune benefits than either compound alone.

Deficiency and Health Implications

Because flavonoids are not essential nutrients in the strict sense, there is no recognised deficiency disease associated with their absence. However, low intake of flavonoid-rich foods may contribute to increased oxidative stress, vascular fragility, and inflammation over time. Epidemiological studies indicate that populations consuming diets rich in fruits, vegetables, tea, and other flavonoid sources have lower risks of cardiovascular diseases, certain cancers, and neurodegenerative disorders.

Therapeutic and Pharmacological Applications

Flavonoids have been incorporated into numerous nutraceutical and pharmaceutical formulations due to their vascular-protective and anti-inflammatory effects. Some notable applications include:

• Treatment of chronic venous insufficiency and varicose veins using diosmin and hesperidin preparations.
• Management of haemorrhoids and capillary fragility.
• Use as adjuvant antioxidants in anti-ageing and cardiovascular health supplements.

Clinical studies continue to explore their potential in preventing metabolic disorders such as diabetes, obesity, and hypertension.

Safety and Toxicology

Flavonoids are generally considered safe when consumed as part of a balanced diet. High doses in supplement form, however, may interfere with the metabolism of certain medications or affect hormone levels due to their mild oestrogenic activity (especially in isoflavones). Long-term excessive supplementation should therefore be approached cautiously and ideally under medical supervision.

Research and Modern Perspectives

Modern research views vitamin P not as a single nutrient but as a broad class of bioactive phytochemicals with diverse functions beneficial to human health. Advanced analytical techniques such as chromatography and spectrophotometry have identified over 6,000 individual flavonoids, each contributing uniquely to plant and human physiology.
Scientific interest in these compounds has expanded to include their roles in neuroprotection, metabolic regulation, and gut microbiota modulation, linking dietary flavonoids to brain health and longevity. Their potential in preventing oxidative stress-related diseases continues to attract attention in nutritional and pharmacological research.