Vitamins, Minerals and Dietary Supplements
What are flavonoids? Why do we need them?
Flavonoids are the name given to a class of water-soluble plant pigments. Flavonoids are often broken down into different categories depending on their actions and the types of food in which they are found.
Some of the most well-known groups of flavonoids are isoflavones, anthocyanidins, flabones, flavanones and flavans. Other important flavonoids include quercetin, rutin, hesperidin and genistein.
Flavonoids are not considered essential nutrients. Nevertheless, some flavonoids appear to have beneficial effects on one's health. Quercetin acts as an antioxidant by controlling blood cholesterol levels. Anthocyanidins may help protect the eyes from developing cataracts. Grapefruit flavonoids are believed to help stop cancerous tumors from forming. Rutin may protect blood vessels and, when taken with vitamin C, can help treat some skin disorders. And soy isoflavones are being investigated to see if they can fight cancer and treat conditions related to menopause. Additional flavonoids may be able to treat conditions ranging from edema and diabetes to glaucoma and heavy menstruation.
How many flavonoids should I take?
While no standard dose of flavonoid has been decided upon, most health care providers recommend that patients take a minimum of 1,000 milligrams of flavonoids one to three times per day. As an alternative, some practitioners recommend an extract of bilberry (standardized to 25 percent anthcyanoside content) at a dose of 240 milligrams to 600 milligrams per day.
What forms of flavonoids are available?
Flavonoids are found in a wide range of foods; different types of flavonoids are found in different foods. For example, soy products are usually heavy in isoflavones and genistein; wines and some types of berries have large amounts of anthocyanidins; quercetin is found in onions, apples and green tea; and citrus fruits are abundant in flavanones. Flavonoids are also available in supplement form, either as a liquid or in tablets and capsules.
What can happen if I take too many flavonoids? Are there any interactions I should be aware of? What precautions should I take?
The only flavonoid shown to have negative side-effects in humans is catechin; large doses may cause fever, anemia and hives, but these symptoms are ameliorated once catechin supplementation is discontinued. Flavonoids often work in conjunction with vitamin C; large amounts can help improve the absorption of vitamin C in the body.
Flavonoids may interact with some drugs used to treat shingles and chickenpox, such as acyclovir. Patients taking these drugs should consult with a licensed health care provider before taking flavonoid supplements. As always, patients should speak with a licensed health care practitioner before taking flavonoids or any other dietary supplements or herbal remedies.
- Kuo SM. Antiproliferative potency of structurally distinct dietary flavonoids on human colon cancer cells. Cancer Lett 1996;110:41-8.
- 12. Knekt P, Javinen R, Seppanen R, et al. Dietary flavonoids and the risk of lung cancer and other malignant neoplasms. Am J Epidemiol 1997;146:223-30.
- Peterson J, Dwyer J. Taxonomic classification helps identify flavonoid-containing foods on a semiquantitative food frequency questionnaire. J Am Diet Assoc 1998;98:682-5.
- So FV, Guthrie N, Chambers AF, et al. Inhibition of human breast cancer cell proliferation and delay of mammary tumorigenesis by flavonoids and citrus juices. Nutr Cancer 1996;26:167-81.
- Reinhold U, Seiter S, Ugurel S, et al. Treatment of progressive pigmented purpura with oral bioflavonoids and ascorbic acid: an open pilot study in 3 patients. J Am Acad Dermatol 1999;41(2 Pt 1):207-8.