What Is It?
Health Benefits
Dosage Information
Guidelines for Use
General Interaction
Possible Side Effects
Evidence Based Rating Scale

What Is It?

Flavonoids is the umbrella term given to some 4,000 compounds that impart the colorful pigment to fruits, vegetables and herbs. Also found in legumes, grains and nuts, flavonoids can act as effective antivirals, anti-inflammatories, antihistamines and antioxidants. They're useful in reducing cancer risk and serve to prevent or treat a wide variety of conditions.

While research generally supports the healing potential of flavonoids, only a few have been widely studied. Some standouts include genistein, found in soybeans and some other legumes; quercetin, found in apples and onions; PCOs (procyanidolic oligomers, also known as proanthocyanidins), found in abundance in pine bark and grape seed Extract, as well as in red wine; citrus flavonoids, including rutin and hesperidin, found in oranges, grapefruits, tangerines and other citrus fruits; and Polyphenols, particularly EGCG (epigallocatechin-gallate), found in green tea. Researchers feel the latter may be the most effective cancer-battling compound discovered to date.

Health Benefits

As antioxidants, flavonoids (or "bioflavonoids" as supplement manufacturers often label them) help prevent the cell damage caused by unstable oxygen molecules known as Free radicals. They provide many other health benefits as well.

Specifically, flavonoids may help to: 

·  Lower cancer risk. A high intake of such flavonoids as polyphenols and quercetin is linked to lower rates of stomach, pancreatic, breast, and prostate cancer (1 – 3). Traditional Chinese Medicine (TCM) relies on prescribing a regimen of many herbal supplements that are high in many types of flavonoids. Research is beginning to show that TCM is successful because of the high flavonoid content of many of its herbal supplement formulations (4). Taking the flavonoid genistein, a phytoestrogen that acts as a weak form of the Hormone estrogen, may help prevent breast cancer and other hormone-related cancers, including prostate cancer (5, 6). Genistein confers this benefit by binding with estrogen receptors in the body's cells. However, research still needs to clarify the optimal dosage level for using flavonoids to treat cancer. Some studies report that favonoid levels must be higher than previously thought to convey anti-tumor benefits (7).


·  Reduce the risk of stroke and heart disease. Studies indicate that a diet high in flavonoids, particularly quercetin and PCOs, may help prevent blood clots and blocked arteries, significantly reducing the chance of death from stroke or heart disease (8 – 10). These bioactive compounds protect against stroke by relaxing the veins and arteries in the head. These studies are still in the animal model phase and have not yet progressed to large-scale human trials. However, more research is being planned on these powerful vascular protective compounds.


·  Protect against age-related vision disorders, such as cataracts and macular degeneration. A contributing factor to the development of cataracts is the accumulation of the sugar sorbitol in the lens of the eye. Studies show that the flavonoids inhibit this buildup. Grape seed extract, another flavonoid, also helps combat cataracts and prevent macular degeneration because it improves blood circulation in the eye (11).


·  Relieve hay fever, sinusitis, and asthma symptoms. Quercetin's proven anti-inflammatory properties help the body counter allergic reactions to pollen. Quercetin also seems to reduce Inflammation in the lungs and other air passages, making breathing easier (12 – 14).


·  Alleviate inflammatory skin conditions, such as eczema and bug bites. Quercetin's anti-inflammatory properties can help treat these skin irritations. In recent research quercetin has even been shown to prevent Collagen breakdown in skin that is beginning to lose collagen due to sun exposure (15). If your skin isn’t looking as firm and supple as you would like with age, you may want to try upping your intake of flavonoids.


·  Reduce inflammation in the joints and muscles common to fibromyalgia, gout, and rheumatoid arthritis. Because of its anti-inflammatory properties quercetin is often used to treat these conditions. Studies have shown that diets high in fruits and vegetables, including vegan (diets containing no animal products) may decrease joint stiffness and pain (16). Adjusting your diet to accommodate more foods high in flavonoids may help promote a healthier lifestyle both inside and out.


·  Minimize menopausal hot flashes and protect post-menopausal women from cardiovascular disease. Genistein, plentiful in soy products, can lessen the symptoms of hot flashes because it can mimic the effects of estrogen in the body. Pure genistein also helps lessen the effects of hot flashes, however it is not as effective as soy (17). The Soy isoflavones also have been shown to have a cardio-protective effect (18). Since women’s risk of heart disease increases drastically after menopause, adding soy isoflavones to your diet can help keep your heart healthy well into your advanced years.


·  Shrink hemorrhoids, reduce varicose veins, and treat leg ulcers. Citrus flavonoids and PCOs help repair hemorrhoids and varicose veins and leg ulcers by strengthening blood vessels (19, 20). However, flavonoid treatment to help speed reduce in pain and bleeding after hemorrhoid surgery did not show any appreciable benefit (21).


·  Battle viral infections. Because flavonoids boost immunity, they help the body fight off illnesses and may speed recovery time. Traditional medical systems such as Ayurvedic and TCM are being increasingly investigated because of the active biochemical compounds that may help battle infections. Researchers are currently postulating that future developments may prove these herbal flavonoid-rich herbal supplements may offer effective anti herpes simplex virus drugs (22).


Note: Flavonoids have also been found to be useful for a number of other disorders. For information on these additional ailments, see the individual flavonoids: quercetin, ginkgo biloba, grape seed extract, green tea, soy isoflavones, and vitamin C and flavonoids

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Dosage Information

·  For overall health: For best results, choose a pure flavonoid supplement that features at least one and possibly a combination of pure flavonoids (such as quercetin, green tea extract, or genistein). Follow the label directions for the exact dosage.

  • Be sure to check out the Dosage Recommendations Charts for the separate flavonoids: quercetin, ginkgo biloba, grape seed extract, green tea, soy isoflavones, and vitamin C and flavonoids.

  • Guidelines for Use


    ·  Take quercetin 20 minutes before a meal; other flavonoids may be taken at any time.

    ·  If you buy a citrus bioflavonoid complex product, look for one that contains some pure rutin, pure hesperidin or both. Mixed citrus bioflavonoid complexes without these may be inexpensive, but they are often less potent.

    ·  Take flavonoids along with vitamin C, if possible, to maximize both of their benefits (flavonoids help increase the absorption of vitamin C). Buying vitamin C and flavonoid supplements separately usually costs less than purchasing a "vitamin C/flavonoid complex" formulation that combines the two; doing so may also provide greater dosage flexibility.

    General Interaction

    ·   Recent studies indicate that taking antioxidants such as flavonoids could decrease the effectiveness of many anti-cancer chemotherapy and radiation treatments if taken at the same time. Restart the antioxidants during the rest period between chemotherapy or radiation treatments.

    ·  Avoid taking a citrus flavonoid preparation containing naringin (a flavonoid present in grapefruit juice but not orange juice) when using an immunosuppressant drug, such as tacrolimus (Prograf).

    ·  Don't take naringin if you are on a calcium channel blocker, such as amlodipine (Norvasc), nifedipine (Procardia) or verapamil (Calan), because it may amplify the effect of the drug and cause a serious drop in blood pressure.

    ·  Naringin may also inhibit the breakdown of various drugs, particularly caffeine, coumarin and estrogens.

    Note: For information on interactions with specific generic drugs, see our WholeHealthMD Drug/Nutrient Interactions Chart.


    Possible Side Effects

    No side effects are presently known.


    Flavonoids should be used as complements to--not replacements for--the standard methods of treating cancer, heart disease and other serious illnesses.  


    1.      Huang SL, Hsu CL, Yen GC. Growth inhibitory effect of quercetin on SW 872 human liposarcoma cells. Life Sci. 2006 Jan 30; [Epub ahead of print]

    2.      Han D, Tachibana H, Yamada K. Inhibition of environmental estrogen-induced proliferation of human breast carcinoma MCF-7 cells by flavonoids. In Vitro Cell Dev Biol Anim. 2001 May;37(5):275-82.

    3.      Vijayababu MR, Kanagaraj P, Arunkumar A, Ilangovan R, Aruldhas MM, Arunakaran J. Quercetin-induced growth inhibition and cell death in prostatic carcinoma cells (PC-3) are associated with increase in p21 and hypophosphorylated retinoblastoma proteins expression. J Cancer Res Clin Oncol. 2005 Nov;131(11):765-71. Epub 2005 Nov 1.

    4.      Guo F, Xu CJ. Progress on the study of mechanism of the direct action of TCM bioactive components on ovarian cancer. Zhongguo Zhong Xi Yi Jie He Za Zhi. 2005 Dec;25(12):1140-4.

    5.      Jeune MA, Kumi-Diaka J, Brown J. Anticancer activities of pomegranate extracts and genistein in human breast cancer cells. J Med Food. 2005 Winter;8(4):469-75.

    6.      Fan S, Meng Q, Auborn K, Carter T, Rosen EM. BRCA1 and BRCA2 as molecular targets for phytochemicals indole-3-carbinol and genistein in breast and prostate cancer cells. Br J Cancer. 2006 Jan 24; [Epub ahead of print]

    7.      van der Woude H, Gliszczynska-Swiglo A, Struijs K, Smeets A, Alink GM, Rietjens IM. Biphasic modulation of cell proliferation by quercetin at concentrations physiologically relevant in humans. Cancer Lett. 2003 Oct 8;200(1):41-7.

    8.      Torregrosa G, Burguete MC, Perez-Asensio FJ, Salom JB, Gil JV, Alborch E. Pharmacological profile of phytoestrogens in cerebral vessels: in vitro study with rabbit basilar artery. Eur J Pharmacol. 2003 Dec 15;482(1-3):227-34.

    9.      Ji ES, Yue H, Wu YM, He RR. Effects of phytoestrogen genistein on myocardial ischemia/reperfusion injury and apoptosis in rabbits. Acta Pharmacol Sin. 2004 Mar;25(3):306-12.

    10.  Tutel'ian VA, Pavliuchkova MS, Pogozheva AV, Vorob'eva LSh, Derbeneva SA. The study of soy isoflavone metabolism in pa

    Date Published: 04/18/2005
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