FLAVONOIDS (bioflavonoids, vitamin P)

Flavonoids are a large family of widely distributed plant substances, formerly designated as vitamin F. However, flavonoids are not classified as essential nutrients, nor do they have a vitamin status. These compounds are often pigments and occur in high concentrations in all fruits, especially CITRUS FRUITS; purple berries and apples; as well as in VEGETABLES, including onions; tea; and whole grains. They are responsible for astringency of certain fruits and tea.

Flavonoids include flavones (such as QUERCETIN), ISOFLAVONES (from soybeans), FLAVANONES (such as naringen and HESPERIDIN and RUTIN from citrus), ANTHOCYANINS (blue, purple, red plant pigments) and flavononols (including catechins, ellagic acid and TANNINS). Typical examples of major flavonoids and common sources are listed in the accompanying table.

Research before World War 11 demonstrated that vitamin C taken with flavonoids (called “”vitamin F”‘ at that time) strengthens capillaries, and in the 1950s flavonoids were frequently prescribed for bleeding. Subsequently the U.S. FDA ruled that they were ineffective despite medical experience to the contrary. Flavonoids have been used as supportive treatment for menstrual bleeding, bruising, frostbite and cold sores.

Flavonoids can also strengthen the blood-brain barrier to increase protection of the nervous system against foreign substances and they help reduce damage due to inflammation, thereby reducing allergy symptoms and allowing tissues to normalize. They accomplish this in the following ways: Flavonoids strengthen and repair connective tissue by stimulating the synthesis of COLLAGEN, the fibrous protein of the connective tissue that holds cells together and by inhibiting collagen breakdown. Furthermore these plant materials slow the infiltration of neutrophils, immune cells that can cause damage, into an inflamed area. Flavonoids also stabilize defensive cells in tissues (mast cells), making them less likely to release substances such as histamine, protein degrading enzymes and LEUKOTRIENES that initiate inflammation. Flavonoids can even block the production of proinflammatory PROSTAGLANDINS as well as leukotrienes and they act as ANTIOXIDANTS to prevent FREE RADICAL damage and lipid oxidation that triggers inflammation. Free radicals are highly reactive molecules that tear electrons away from neighboring molecules to make up for their own deficiency.

Population studies indicate that consumption of flavonoids from tea, onions and apples by northern European men can decrease the risk of heart attack, and the consumption of black tea is associated with a lower risk of STROKE. Two properties may account for these effects. Flavonoids make small blood cells called platelets less sticky, thus they can reduce the risk of dangerous blood clots. Flavonoids also act, as antioxidants, possibly preventing the oxidation of LDL-cholesterol, believed to be an initiating event in atherosclerosis. Other studies suggest that certain flavonoids block cancers (anticarcinogenic activity). They can activate or inhibit various DETOXICATION enzymes in the liver; thus they may prevent the activation of carcinogens.

The amounts of key flavonoids in foods and beverages have been determined and dietary intakes can be computed. How much of a given flavonoid needs to be consumed to achieve a protective effect is uncertain, though a diet that provides 25 to 50 mg of key flavonoids offers a degree of protection against heart diseaseSome flavonoids are:

Anthcyanin – found in black berries, blueberries, raspberries

Ellagic Acid – found in strawberries, grapes, apples, cranberries

Catechin – found in green tea, black tea

Tannin – found in green tea, black tea

Kaempferol – found in strawberries, leeks, kale, broccoli, radishes

Quercetin – found in green tea, onions, red cabbage, green beans

Hertog, MichaM G.L., Feskens, Edith J.M., Hollman, Peter C.H., Katan, M.B., and Kromhouty, D., “‘Dietary Antioxidant Flavonoids and Risk of Coronary Heart Disease: The Zutphen Elderly Study,”‘ Lancet, 342 (October 23, 1993), pp. 1007-11.