flavonoid

Flavonoids are a diverse group of polyphenolic compounds produced by plants. They are secondary metabolites found in many fruits, vegetables, grains, tea, wine, and herbs. They share a common chemical structure, a 15-carbon skeleton consisting of two phenyl rings (A and B) and a heterocyclic ring (C), giving the general C6-C3-C6 framework, often with various oxygen-containing functional groups.

Based on their chemical structure, flavonoids are classified into several major subclasses: flavonols (such as quercetin and kaempferol), flavones (apigenin, luteolin), flavanones (naringenin, hesperetin), isoflavones (genistein, daidzein), anthocyanidins/anthocyanins (delphinidin, cyanidin), and flavan-3-ols (catechins) and their polymers (proanthocyanidins). They frequently occur as glycosides in plants, and may form polymeric proanthocyanidins.

In plants, flavonoids originate from the phenylpropanoid pathway and contribute to pigmentation, UV filtration, plant defense, and signaling. They accumulate in vacuoles and can impact flower color and fruit coloration that attracts pollinators.

In humans, dietary flavonoids are studied for antioxidant, anti-inflammatory, and cardiometabolic effects. Evidence from observational studies suggests associations with reduced disease risk, but results from clinical trials are mixed and often confounded by diet. Flavonoids are not essential nutrients; they are absorbed in the gut after deglycosylation and may be metabolized by gut microbiota into various compounds.

Research and terminology: The term flavonoid covers a broad class of compounds distinct from other polyphenols, and analytical methods distinguish subclasses and glycosides.