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Flavonoids
Also indexed as: Bioflavonoids
Flavonoids are a class of water-soluble plant pigments. Flavonoids are broken down into categories, though the issue of how to divide them is not universally agreed upon. One system breaks flavonoids into isoflavones, anthocyanidins, flavans, flavonols, flavones, and flavanones.1 Some of the best-known flavonoids, such as genistein in soy, and quercetin in onions, can be considered subcategories of categories. Although they are all structurally related, their functions are different. Flavonoids also include hesperidin, rutin, citrus flavonoids, and a variety of other supplements.
Where are they found?
Flavonoids are found in a wide range of foods. For example, flavanones are in citrus, isoflavones in soy products, anthocyanidins in wine and bilberry, and flavans in apples and tea.
Flavonoids have been used in connection with the following conditions (refer to the individual health concern for complete information):
| Science Ratings | Health Concerns |
|---|---|
 |
Chronic venous insufficiency (rutin) Edema (water retention) (coumarin, hydroxyethylrutosides) Hepatitis (catechin) |
 |
Bruising Cold sores Diabetes (bilberry) Dysmenorrhea (rutin plus vitamin B3 [niacin] and vitamin C) Edema (water retention) (diosmin and hesperidin combination) Gingivitis (periodontal disease) (in combination with vitamin C) Hemorrhoids (hydroxyethylrutosides derived from rutin) Ménière’s disease (hydroxyethylrutosides) Retinopathy (bilberry) Skin ulcers (diosmin, hesperidin) |
 |
Allergies Atherosclerosis (quercetin, bilberry) Cancer (naringenin) Capillary fragility (hesperidin, quercetin, rutin) Cataracts (quercetin, bilberry) Diabetes (quercetin) Edema (water retention) (quercetin) Gingivitis (periodontal disease) Glaucoma (rutin) Hay fever (quercetin, hesperidin, rutin) Macular degeneration (bilberry) Measles Menopause (hesperidin) Menorrhagia (heavy menstruation) Night blindness (bilberry) Peptic ulcer (quercetin) Progressive pigmented purpura (in combination with vitamin C) Retinopathy (quercetin, rutin) |
| Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit. |
|
Who is likely to be deficient?
Flavonoid deficiencies have not been reported.
How much is usually taken?
Flavonoid supplements are not required to prevent deficiencies in people eating a healthy diet. Healthcare practitioners commonly recommend 1,000 mg of citrus flavonoids taken one to three times per day. Alternatively, 240–600 mg of bilberry (standardized to 25% anthcyanosides) may be taken per day.
Are there any side effects or interactions?
No consistent side effects have been linked to the flavonoids except for catechin, which can occasionally cause fever, anemia from breakdown of red blood cells, and hives.2 3 These side effects subsided when treatment was discontinued.
In 1980, quercetin was reported to induce cancer in animals.4 Most further research did not find this to be true, however.5 6 While quercetin is mutagenic in test tube studies, it does not appear to be mutagenic in animal studies.7 In fact, quercetin has been found to inhibit both tumor promoters8 and human cancer cells.9 People who eat high levels of flavonoids have been found to have an overall lower risk of getting a wide variety of cancers,10 though preliminary human research studying only foods high in quercetin has found no relation to cancer risk one way or the other.11 Despite the confusion, in recent years experts have shifted their view of quercetin from concerns that it might cause cancer in test tube studies to guarded hope that quercetin has anticancer effects in humans.12
The flavonoids work in conjunction with vitamin C. Citrus flavonoids, in particular, improve the absorption of vitamin C.13 14
Are there any drug
interactions?
Certain medicines may interact with flavonoids. Refer to drug interactions for a list of those medicines.
References
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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires September 2008.