Flavonoids are a group of plant pigments which determine the color of many fruits and vegetables. Over 4,000 flavonoids have been detected and classified according to chemical structure. One common source for them is the white covering of the segments in citrus fruits. The whole segments of the fruit contain ten times more bioflavonoid activity than the strained juice (1).
The most beneficial group of plant flavonoids is the proanthocyanidins. These are commercially available as grape seed extract and extract of the maritime pine bark, although the grape seed has a more potent effect. They are anti-oxidants, but are much more powerful than Vitamin C or E. The value of these compounds is their ability to "increase intracellular vitamin C levels, decrease capillary permeability and fragility, scavenge oxidants and free radicals, and inhibit destruction of collagen...PCO extracts also prevent the release and synthesis of compounds that promote inflammation and allergies" (2). These compounds are extremely important in the prevention and treatment of cancer, heart disease, and arthritis, as well as the aging process, and virtually every chronic degenerative disease that exists.
Quercetin is the most potent and active of the flavonoids in medical studies. It is the base for the citrus flavonoids, including rutin, quercitrin, and hesperidin. These other flavonoids have Quercetin in combination with sugar molecules. Quercetin has a significant anti-inflammatory effect. It is also an inhibitor of the enzyme aldose reductase, the enzyme responsible for the conversion of blood sugar to sorbitol, a compound strongly implicated in the development of diabetic complications (3). Quercetin is a phytoestrogen, which means that it has an anti-estrogenic effect which could lead to a reduced risk of some kinds of cancer (4). It has been found to inhibit breast cancer cells in a test tube (5). Quercetin has the greatest anti-viral activity against normal viral infections such as the common cold, as well as herpes virus type I, para-influenzae 3, polio virus type I, and respiratory syncytial virus. Quercetin is also the most effective of all the flavonoids at inhibiting tumor growth (6).
Most of the research on citrus bioflavonoids have used the flavonoid Rutin. Specifically, a combination of rutinosides called hydroxyethylrutosides (HER) has been used with impressive results. It has been used in the treatment of varicose veins, hemorrhoids, diabetic vascular disease, and diabetic retinopathy. One of the chief benefits of bioflavonoids is that they increase the blood flow through the small blood vessels. Mixed preparations of bioflavonoids are the most widely used and the cheapest, but are also the least active. Preparations containing pure rutin and hesperidin, or HER are the best.
Green Tea Polyphenols are of great use in the treatment of cancer. Both green tea and black come from the same plant, but while green tea leaves are lightly steamed to produce the tea, black tea leaves are actually allowed to oxidize first. Black tea can actually make some cancers worse, while green tea, made from the same plant, can protect against many types of cancers. It does this by blocking the formation of certain types of cancer-causing compounds, suppressing the activation of carcinogens, and detoxifying these cancer-causing agents. It also inhibits tumor growth.
In my opinion, bioflavonoids of all kinds need to be part of everyone's diet, through direct eating of citrus and other fruits, as well as through supplementation. With cancer on the rise, and so many carcinogenic chemicals in our environment and our diets, we cannot afford not to supplement our diets with these wonderful gifts from nature.
Ailments which might benefit from Bioflavonoid supplementation:
Cancers, especially breast cancer
Diabetic vascular disease (8).
Nutritional sources of various bioflavonoids:
Grapefruit, oranges, apples, apricots, pears, peaches, tomatoes, blueberries, cherries, cranberries, cowberries, currants, black, grapes, red plums, yellow and blue raspberries, black and red strawberries, hawthorn berries, red cabbage, onions, parsley, rhubarb, dried beans, sage, green tea, red wine (9).
Toxicity information: Proanthocyanidins - none, no toxic effects reported, even at high dosages. Quercetin - no toxic effects found in dosages even up to 2000 milligrams per kilogram of body weight for as long as two years. Citrus bioflavonoids - no toxic side effects of any kind reported. Green tea polyphenols - no significant side effects. Green tea does contain caffeine, and may produce a stimulant effect in some; however, it does not appear to produce these symptoms in many people who are normally sensitive to caffeine. All these bioflavonoid compounds are considered safe during pregnancy.
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Copyright 2015 Judie C. McMath and The Center for Unhindered Living
(1) Dunne, Lavon J. (1990). Nutrition Almanac, 3rd ed. New York: McGraw-Hill, p. 60.
(2) Murray, Michael T. (1996). The Encylcopedia of Nutritional Supplements. Rocklin, CA: Prima Publishing, p. 323.
(3) Murray, as in (2) above, p. 324.
(4) Healthnotes, Inc. (2000). "Quercetin." Available Online: [http://www.healthwell.com/healthnotes/Supp/Quercetin.cfm].
(5) Miodini P, Fioravanti L, di Fronzo G, Capelletti V. The two phyto-oestrogens genistein and quercetin exert different effects on oestrogen receptor function. Br J Cancer 1999;80:1150–5.
(6) Murray, as in (2) above, p. 325.
(7) Dunne, as in (1) above, p. 62.
(8) Murray, as in (2) above, pp. 326-328.