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Home Nutritional Supplements Flavonoids
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What do citrus fruits, grape seed extract, red wine, pine bark extract and onions have in common?  The answer is they're all good sources of flavonoids, the plant pigments that help fight a host of disorders, from cataracts and cancer to hay fever and menopausal hot flushes.

What they are?

More than 4000 flavonoids (or bioflavonoids, as they are sometimes called on supplement labels) have been identified, and scientists suspect that there may be many more still to be discovered in nature.  Flavonoids give colour to fruits, vegetables and herbs, and are found in legumes and grains, as well as nuts.  They are also potent antioxidants – some are even more powerful than vitamin E in preventing the cell damage caused by unstable oxygen molecules (free radicals).  So far, only a few flavonoids have been investigated for their healing potential.

One of these, quercetin (found in onions and apples), also serves as a building block for other flavonoids.  Rutin and hesperidin are the most active of the so-called citrus flavonoids, which, as the name suggests, are present in oranges, grapefruit, mandarins and other citrus fruits.

Other flavonoids include PCOs (or procyanidolic oligomers; also called proanthocyanidins), anthocyanosides, polyphenols and genistein.  PCOs are plentiful in pine bark and grape seed extracts, and in red wine.  Anthocyanosides are found in the herb bilberry.  Green tea is the primary source of polyphenols, especially EGCG (epigallocatechin-gallate), which experts believe is possibly the most effective cancer-fighting compound yet discovered.  Genistein, found in soy products, has antioxidant properties and can also mimic the effects of oestrogen.  (For more information, see the entries on these individual supplements as well.)

What they do?

The disease-fighting potential of flavonoids stems from their ability to reduce inflammation, prevent the release of histamine (which causes allergy symptoms such as congestion), fight free radicals, boost immunity, strengthen blood vessel walls and increase blood flow, among other properties.


The flavonoids quercetin and PCOs may protect against heart disease and other circulatory disorders because they inhibit bodily changes that can lead to blocked arteries.  They also help to strengthen blood vessels in a variety of ways.  Studies from Finland and the Netherlands found that people who get plenty of flavonoids, particularly quercetin, have a reduced risk of developing heart disease or having a stroke.  In one study, a diet high in flavonoids appeared to cut the chances of dying from heart disease by 50% in women and 23% in men.  Another study reported a 75% drop in stroke risk for men who had the highest intake of flavonoids, compared with those who had the lowest.

Polyphenols and quercetin have shown promise as anti-cancer compounds.  Studies found lower rates of stomach, pancreatic, lung and possibly breast cancer in people with a high intake of these flavonoids.  In addition, soy-based genistein may help to fight breast cancer and minimize hot flushes by interacting with oestrogen receptors in the body.  quercetin also helps the body to use blood sugar and so may be valuable in preventing diabetes.  Furthermore, it inhibits the build-up of sorbitol (a type of sugar) in the lens of the eye, a cause of cataracts.

Additional Benefits

Quercetin may help to relive hay fever, sinusitis and asthma because it can block allergic reactions to pollen and reduce inflammation in the airways and lungs.  This anti-inflammatory action also makes it useful for insect bites, eczema and related skin conditions, as well as for inflammatory disorders of the joints and muscles, such as rheumatoid arthritis, gout and fibromyalgia.  Because they strengthen blood vessels, PCOs and citrus flavonoids are helpful in repairing varicose veins and haemorrhoids.  Rutin and hesperidin play a role in preventing bruising.

Common Uses

  • Reduce the risk of heart disease.
  • May prevent breast, prostate and other types of cancer.
  • Lessen the chance of age-related vision problems, such as cataracts or macular degeneration.
  • Minimize the symptoms of hay fever and asthma.
  • Fight viral infections.


  • Capsule.
  • Tablet.
  • Powder.
  • Liquid.


  • Reminder:  If you have a medical condition, talk to your doctor before taking supplements.

How to take it?


For general health benefits:  Buy a flavonoids mixture that contains several types (such as quercetin, rutin and hesperidin) and follow the dosage instructions on the label.

For allergies, asthma, gout and insect bites:  Take 500 mg of quercetin two or three times a day with 400 mg of bromelain.

Guidelines for use:

Grape seed extract and green tea are excellent sources of flavonoids and exert an antioxidant effect as well.  It's usually best to combine flavonoids with vitamin C to enhance their protective properties.  Quercetin should be taken 20 minutes before meals; other flavonoids can be taken at any time of the day.

Possible side effects

There are no known toxicities, adverse reactions or other side effects from flavonoids.

Shopping Hints

  • Mixed preparations of citrus flavonoids are the most widely available and the least expensive supplements of this type.  But they are also the least active, often providing a flavonoids content of only 50%.  You'll get more value for your dollar by choosing preparations that contain pure rutin or pure hesperidin, or a combination of these two.
  • Flavonoids are sometimes mixed with vitamin C, and the combination is labeled and sold as vitamin C complex.  It's usually less expensive, however, to buy vitamin C and flavonoids separately, which also allows you to vary your dose as needed.  Flavonoids improve the absorption of vitamin C.

Latest Findings

Eating an apple a day has always been associated with good health, and a recent US study suggests that quercetin may be the magic ingredient.  Lung cancer risk fell by 58% in people who ate the most apples (a major source of quercetin) compared with those who ate the fewest apples.