Several hundred flavones and flavonol aglycones are known, but only three are common: kaempferol, quercetin, and myricetin.
Quercetin has the widest distribution in nature of phenolic compounds, and 135 different glycosides of quercetin.
It is the potent flavonoid and antioxidant found naturally in the pulp of many citrus fruits and in apple skins, buckwheat, red onions, red grapes, wine, and tea. Quercetin also found in onions, cayenne pepper, and garlic.
It is estimated that the average adult diet provides up to 50 mg of quercetin each day.
Evidence indicates that quercetin has antiviral activity, both in vivo and in vitro, most markedly against herpes simplex type I, para-influenza types 3, polio virus type I, and respiratory syncytial virus.
In cardiovascular system, it prevents free radicals from oxidizing low-density lipoproteins (LDL). If LDL becomes oxidized, it will be precursor to arterial damage and atherosclerosis.
However, hypersensitive individuals may experience headaches or tingling. While rare, other reported side effects include gastrointestinal discomfort, hematoma, and kidney toxicity.
Quercetin in food
