Quercetin is a flavonoid and more specifically a flavonol. In studies, Quercetin had been found to be the most active of the flavonoids. Many medicinal plants owe much of their activity to their high quercetin content. Quercetin has demonstrated significant anti-inflamatory properties, has shown remarkable anti-tumor properties and may have positive effects in combating cancer, prostatitis, heart disease, cataracts, allergies and respiratory diseases. Foods rich in Quercetin include apples, tea, onions (higher concentrations of Quercetin occur in ther outermost rings), red grapes, citrus fruits, chokeberry, sweet rowan, rowanberry, sea blckthorn berry, respberry, prickly pear cactur, broccoli, other leafy green vegetables, and many other foods.