flavonols

Flavonols are a class of flavonoids, a diverse group of polyphenolic compounds found in many fruits, vegetables, and beverages. They share a common flavone backbone with a C6-C3-C6 skeleton, a double bond between positions 2 and 3, and a carbonyl at position 4. In flavonols the 3-hydroxyl group is present on the central ring, and many occur as glycosides in which sugars are attached to hydroxyl groups. The best known aglycones are quercetin, kaempferol, and myricetin; other flavonols include fisetin, galangin, and isorhamnetin.

Dietary sources are diverse and include onions, apples, berries, grapes, leafy vegetables, tea, and wine; broccoli, citrus fruits, and whole grains also contribute. In foods these compounds often exist as glycosides such as quercetin-3-O-glucoside or rutin (quercetin-3-O-rutinoside). After ingestion, deglycosylation by intestinal enzymes or gut microbiota allows absorption and metabolism to various conjugates.

In plants, flavonols are produced via the phenylpropanoid pathway and are formed from dihydroflavonol precursors by flavonol synthase. They serve roles in plants as UV protection, pigmentation, and defense against pathogens.

Research into their health effects in humans reports antioxidant, anti-inflammatory, and potential cardiometabolic benefits, but human evidence is variable and often limited by bioavailability and study design. Flavonols are generally consumed as part of a normal diet; high-dose supplements can have interactions with medications and are not universally recommended.