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Bioflavonoids, also known as flavonoids, are a group of plant pigments which give colour to many flowers and fruits. These colourful biochemical compounds provide protection against and treat many diseases. There are over 4000 known bioflavonoids; this page will focus on four main categories including proanthocyanidins, quercetin, citrus bioflavonoids, and green tea polyphenols..
As a group, bioflavonoids have anti-inflammatory, antiallergic, antiviral, and anticarcinogenic properties. They are also powerful antioxidants. In fact, high bioflavonoid intake has been associated with a decrease risk of heart attack due to their antioxidant effects on cholesterol.
- Proanthocyanidins is one of the most beneficial groups of plant bioflavonoids. When proanthocyanidins are linked together, they are referred to as procyanidolic oligomers or PCOs. Their benefits are many, including their ability to increase intracellular vitamin C, decrease capillary permeability and fragility, scavenge oxidants and free radicals, and inhibit collage destruction. PCO extracts can also inhibit mediators which initiate inflammation and allergic reactions. The antioxidant effects of PCO are actually greater than those of vitamin C and vitamin E. PCOs exist in many plants and red wine, and can be found commercially in grape seed extract and extract from the bark of the maritime pine.
- Quercetin has significant anti-inflammatory effects. It inhibits the synthesis and release of histamine and other inflammatory mediators. It also acts as a powerful antioxidant. It appears that quercetin is the most effective bioflavonoid in terms of its antiviral and anticancer actions.
- Citrus Flavonoids exert many of the same beneficial effects as PCOs such as antioxidant activity, ability to increase intracellular vitamin C and benefits to capillary permeability and blood flow. They also have anti-allergy and anti-inflammatory actions similar to quercetin.
- Green Tea Polyphenols have antioxidant activity that is more potent than that of vitamin C and vitamin E. Green tea polyphenols also increase the antioxidant action of various enzymes within the body such as glutathione peroxidase. This antioxidant action has contributed to the anticancer effects that green tea polyphenols also possess 
The following foods have the highest concentration of bioflavonoids.
The following are the primary uses for bioflavonoids, broken down into four major categories: 
- Cardiovascular disease and stroke prevention: The ability for PCOs to protect against these disease is largely due to its antioxidant action. Animal studies have shown that PCO extracts prevent damage to cholesterol and the lining of arteries, and lower blood cholesterol and decrease the size of cholesterol deposits in arteries. They also decrease platelet aggregation and vascular constriction.
- Venous and capillary disorders: such as venous insufficiency, varicose veins, capillary fragility, and disorders of the retina such as diabetic retinopathy and macular degeneration.
- Visual function: Grape seed PCO extract supplementation aids in visual functioning even in healthy individuals. This improvement is due to improved retinal functioning.
- Inflammatory and allergic conditions such as asthma, hayfever, rheumatoid arthritis, and Lupus erythematosus.
- Type II Diabetes: Quercetin has been used for the treatment of a variety of diabetic complications such as diabetic cataracts, peripheral neuropathy, and retinopathy. In the case of cataracts, quercetin acts by inhibiting the enzyme aldose reductase which is responsible for converting extra glucose in the body into sorbitol. Sorbitol accumulates in the lens of the eye, drawing with it water, in order to maintain an osmotic balance. The cells then release important molecules such as amino acids, inositol, glutathione, niacin, vitamin C, magnesium, and potassium. The loss of these compounds make the lens more susceptible to damage and thus lead to cataract formation. Quercetin can act to decrease the amount of sorbitol in the lens. Furthermore, quercetin enhances the secretion of insulin, protects pancreatic beta-cells, and inhibits platelet aggregation.
- Cancer: Quercetin exhibits anticancer effects against a variety of cancers including squamous cell carcinoma, leukemia, and cancers of the breast, ovaries, colon and rectum, and brain. Human studies are needed to confirm these findings from in vitro studies.
- Viral Infections: Quercetin has the greatest antiviral activity of the bioflavonoids. It has its greatest effect against herpes virus type I, para-influenza 3, polio virus type I, and respiratory syncytial virus. Quercetin is indicated for use in the common cold.
- Bruising and nosebleeds: Rutin, a citrus bioflavonoid, was used in many of the early studies and showed benefit for sports injuries causing bruising and also nosebleeds. It appears to reduce capillary fragility and decrease bruising and swelling.
- Venous Insufficiency: Hydroxyethylrutosides (HER), another citrus bioflavonoid, has been used in more recent studies and has been shown to be beneficial for such conditions as varicose veins, hemorrhoids (also hemorrhoids related to pregnancy), diabetic vascular disease, and diabetic retinopathy.
- Cancer Prevention: Green tea polyphenols have been shown to block the formation of such compounds as nitrosamine which is a cancer-causing compound. They also suppress the activation of carcinogens and aid in detoxifying cancer-causing agents. All of this has been shown in in vitro studies. Humans studies also support the notion that green tea polyphenols exert a protective effect against various cancers including gastrointestinal cancers such as cancers of the stomach, small intestine, pancreas, and colon; lung cancer, and estrogen
-related cancers such as breast cancer. Drinking green tea with meals is particularly protective as green tea polyphenols inhibit the formation of nitrosamines. Nitrosamine is formed from nitrites which are found in cured and smoked meats. Excessive nitrate ingestion increases one's risk of developing cancer but green tea exhibits an inhibitory effect on these compounds, protecting the body from many of their harmful effects.
The recommended dosages have not yet been established. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Adult 
- Proanthocyanidins: 50mg (preventive antioxidant support); 150-300mg (therapeutic dose)
- Quercetin: 200-400mg 20 minutes before meals, three times a day
- Citrus Bioflavonoids: 1000-3000mg (therapeutic dose of HER); for dose of citrus flavonoids, rutin, and hesperidin, multiply by 2 (2000-6000mg daily)
- Green Tea Polyphenols: 300-400mg (green tea extract standardized to 80% total polyphenol and 55% epigallacatechin gallate content) -OR- 3 cups of green tea daily or 3g of soluble components providing approximately 240-320mg of polyphenols.
- Proanthocyanidins: grape seed extracts are available that contain a total of 92% or 95% PCO, pine bark extracts can vary from 80-85%. Grape seed extract may be more potent and effective than the extract of pine bark due to its gallic ester content. Grape seed extract provides greater value at a lower price.
- Quercetin: available in powder and capsule forms. For best anti-inflammatory effects, products that provide a combination of the pineapple enzyme bromelain may provide additional benefit. The amount of bromelain should be equal to the amount of quercetin
- Citrus Bioflavonoids: mixed citrus bioflavonoids are the least active. Preparation containing rutin and hesperidin or those that clearly state the levels of rutin and hesperidin are a better buy than those products who do not quantify specific flavonoids. HER are probably the better choice when opting for the benefits in this class of flavonoids
- Green Tea Polyphenols: You can find commercial preparations of green tea polyphenols that have been decaffeinated and concentrated for polyphenols (60-80%). One cup of green tea may contain as much as 300-400mg of polyphenols but also contains 50-100mg of caffeine.
Bioflavonoids are generally safe for most individuals and side effects and toxicity are typically rare. Noted precautions include:
- Citrus Bioflavonoid preparation containing naringin: Naringin is found in grapefruit juice and can increase the bioavailability of such drugs as Nifedipine, Felodipine, Verapramil, and Terfenadine. It can also inhibit the breakdown of some drugs and compounds including Caffeine, Coumarin, and Estrogen. Avoid grapefruit juice and flavonoid preparations containing naringin when taking any of these drugs.
- Drug Interactions:
- Cyclosporin: Co-administration with quercetin increases the bioavailability of orally administered cyclosporin.
- Nutritient Interactions:
- Murray Michael T (1996) Encyclopedia of Nutritional Supplements: The Essential Guide for Improving Your Health Naturally, Prima Publishing. Cite error: Invalid
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- Gaby AR (2011) Nutritional Medicine, Fritz Perlberg Publishing.