Flavonoids are a group of chemical compounds, low molecular weight phenylbenzopyrones, found in all vascular plants. In the diet, flavonoids are found in many fruits, vegetables, teas, wines, nuts, seeds, and roots. Many of the medicinal actions of foods, juices, herbs, and bee pollen are directly related to their flavonoid content. Although not considered vitamins, flavonoids have a number of nutritional functions have been described as biological response modifiers; most act as antioxidants, and some have anti-inflammatory properties. Flavonoids have been shown to prevent or slow the development of some cancers.

Cocoa, particularly dark chocolate, is loaded with the flavonoid Epicatechin and has been found to have nearly twice the antioxidants of red wine and up to three times those found in green tea. The Epicatechin improves blood flow and thus good for cardiac health.

Over 4000 flavonoid compounds have been characterized and classified according to chemical structure. They are usually subdivided into 5 subgroups:
Flavonols: Quercetin, Kaempferol, Myricetin, Isorhamnetin
Flavones: Luteolin, Apigenin
Flavanones: Hesperetin, Naringenin, Eriodictyol
Flavan-3-ols: (+)-Catechin, (+)-Gallocatechin, (-)-Epicatechin, (-)-*Epigallocatechin, (-)-Epicatechin 3-gallate, (-)-Epigallocatechin 3-gallate, Theaflavin, Theaflavin 3-gallate, Theaflavin 3'-gallate, Theaflavin 3,3' digallate, Thearubigins
Anthocyanidins: Cyanidin, Delphinidin, Malvidin, Pelargonidin, Peonidin, Petunidin

One of the most beneficial groups of plant flavonoids is the proanthocyanidins. These flavonoids provide many health-promoting benefits.

Quercetin - Quercetin is a flavonoid that serves as the backbone for many other flavonoids, including the citrus flavonoids rutin, quercitrin, and hesperidin. Quercetin is consistently the most active of the flavonoids in experimental studies, and many medicinal plants owe much of their activity to their high quercitin content.

Citrus Bioflavonoids - Citrus bioflavonoids preparations can include rutin, hesperidin, quercitrin, and naringin. Hydroxyethylrutosides (HER) have been used in the treatment of capillary permeability, easy bruising, hemorroids, and varicose veins.

Green Tea - Both green tea and black tea are derived from the same plant (Camellia sinensis). Green tea is produced by lightly steaming the fresh-cut leaf, while to produce black tea the leaves are allowed to oxidize. During oxidation, enzymes present in the tea convert many "polyphenol" substances that possess outstanding therapeutic action to compounds with much less activity. With green tea, oxidation is not allowed to take place because the steaming process inactivates these enzymes. The term polyphenol denotes the presence of a phenolic ring in the chemical structure. The major polyphenols in green tea are flavonoids (catechin, epicatechin, epicatechin gallate, epigallocatechin gallate, and proanthocyanidins).

Key Benefits - As a class of compounds, flavonoids have been referred to as "nature's biological response modifiers" because of their ability to modify the body's reaction to other compounds such as allergens, viruses, and carcinogenic properties. In addition, flavonoids act as powerful antioxidants by providing remarkable protection against oxidative and free-radical damage.

Proanthocyanidins extracts demonstrate a wide range of pharmacological activity. Their effects include:
Increase intracellular vitamin C levels.
Decrease capillary permeability and fragility.
Scavenge oxidants and free radicals.
Inhibit destruction of collagen the most abundant protein in the body.
Quercetin has demonstrated significant anti-inflammatory activity because of direct inhibition of several initial processes of inflammation. For example, it inhibits both the manufacture and release of histamine and other allergic/inflammatory mediators. In addition, it exerts potent antioxidant activity and vitamin C-sparing action.

Citrus Flavonoids - In addition to possesing antioxidant activity and an ability to increase intracellular levels of vitamin C, rutin, and hesperidin exert many beneficial effects on capillary permeability and blood flow. They exhibit also some of the anti-allergy and anti-inflammatory benefits of quercetin.

Green Tea - Green tea polyphenols are potent antioxidant compounds that have demonstrated greater antioxidant protection than vitamins C and E. Green tea may also increase the activity of antioxidant enzymes. Green tea polyphenols inhibit cancer by blocking the formation of cancer-causing compounds and suppressing the activation of carcinogens.

Food sources - Good sources of flavonoids include citrus fruits, berries, onions, parsley, legumes, green tea, red wine, and dark chocolate with a cocoa content of seventy percent or greater.

Flavonoids Links and Resources
USDA Database of Flavonoid content of food (pdf)
Flavonoids (chemistry)
Cornell news on Cocoa
Balch, J. F., & Balch, P. A. (2000). Prescription for Nutritional Healing. New York: Avery, Penguin Putnam Inc.
Murray, M. T. (1996). Encyclopedia of Nutritional Supplements. Roseville: Prima Publishing.

Recommended Products Containing Flavonoids
Lipidol for Cholesterol Control.
Green Tea Capsules - Caffeine Free and highest levels of pure Polyphenols I have ever seen.
This brand of Multivitamins contain several Flavonoids. Why take different supplements when one can cover everything.