While they are not considered essential nutrients, some flavonoids support health by strengthening capillaries and other connective tissue, and some function as anti-inflammatory, antihistaminic, and antiviral agents. Quercetin has been reported to block the "sorbitol pathway" that is linked to many problems associated with diabetes. Rutin and several other flavonoids may also protect blood vessels.

As antioxidants, some flavonoids, such as quercetin, protect LDL ("bad") cholesterol from oxidative damage. Others, such as the anthocyanidins from bilberry, purple cabbage, and grapes, may help protect the lens of the eye from cataracts. Animal research suggests that naringenin, found in grapefruit, may have anticancer activity.2 Soya isoflavones are also currently being studied to see if they help fight cancer.

In a small, preliminary trial, rutoside (500 mg twice daily), a derivative of the flavonoid, rutin, combined with vitamin C (500 mg twice daily) produced marked improvement in three women with progressive pigmented purpura (PPP), a mild skin condition.3 Although not a serious medical condition, cosmetic concerns lead persons with PPP to seek treatment with a variety of drugs. The vitamin C/rutoside combination represents a promising, non-toxic alternative to these drug treatments, but larger, controlled trials are needed to confirm these preliminary results.

Where are they found? Bioflavonoids are found in a wide range of foods. For example, flavanones are in citrus, isoflavones in soya products, anthocyanidins in wine and bilberry, and flavans in apples and tea.