Flavonoids and Food that Contain Them
Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2011/02/14 - Updated: 2022/06/03
Topic: Antioxidants and Carotenoids - Publications List
Page Content: Synopsis - Introduction - Main
Synopsis: Information on flavonoids including examples of foods fruits and vegetables containing flavonoids that have beneficial health properties. Flavonoids, or bioflavonoids, also collectively known as Vitamin P and citrin, are a class of plant secondary metabolites or yellow pigments having a structure similar to that of flavones. Flavones are mainly found in cereals and herbs.
Introduction
What are Flavonoids?
Flavonoids are synthesized only in plants. They are a diverse group of phytochemicals, exceeding four thousand in number. Flavonoids are compounds found in fruits, vegetables, and certain beverages that have diverse beneficial biochemical and antioxidant effects. Their dietary intake is quite high compared to other dietary antioxidants like vitamins C and E. The antioxidant activity of flavonoids depends on their molecular structure, and structural characteristics of certain flavonoids found in hops and beer confer surprisingly potent antioxidant activity exceeding that of red wine, tea, or soy.
Main Item
Flavonoids, or bioflavonoids, also collectively known as Vitamin P and citrin, are a class of plant secondary metabolites or yellow pigments having a structure similar to that of flavones. Flavones are mainly found in cereals and herbs and are said to have beneficial effects against atherosclerosis, osteoporosis, diabetes mellitus and certain cancers. Flavones intake in the form of dietary supplements and plant extracts has been steadily increasing.
Flavonoids are the most important plant pigments for flower coloration producing yellow or red/blue pigmentation in petals designed to attract pollinator animals. Flavonoids (specifically flavonoids such as the catechins) are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants". Preliminary research indicates that flavonoids may modify allergens, viruses, and carcinogens, and so may be biological "response modifiers". In vitro studies of flavonoids have displayed anti-allergic, anti-inflammatory, anti-microbial, and anti-cancer activities.
Recently consumers and food manufacturers have become interested in flavonoids for their possible medicinal properties, especially their putative role in the prevention of cancers and cardiovascular diseases. Although physiological evidence is not yet established, the beneficial effects of fruits, vegetables, tea, and red wine have sometimes been attributed to flavonoid compounds. Some research also indicates flavonoids may help prevent tooth decay and reduce the occurrence of common ailments such as the flu.
The results of a study published in the journal Nutrition and Cancer conducted in Italy over the past 20 years found that a high flavonoid diet played a key role in cancer prevention. Study participants with the highest intake of flavonoids and proanthocyanidins demonstrated a 44% lower risk of oral cancer and a 40% reduced occurrence of laryngeal cancer. Incidence of colon cancer was lowered by a third and reductions in breast, ovarian, and kidney cancers were noted as well.
Physiological processing of unwanted flavonoid compounds induces so-called Phase II enzymes that also help to eliminate mutagens and carcinogens, and therefore may be of value in cancer prevention. Flavonoids could also induce mechanisms that may kill cancer cells and inhibit tumor invasion. In preliminary studies, UCLA cancer researchers have proposed those study participants who ate foods containing certain flavonoids, such as catechins found in strawberries and green and black teas; kaempferol from Brussel sprouts and apples; and quercetin from beans, onions, and apples, may have reduced risk of obtaining lung cancer. Taking large dietary supplements likely provides no extra benefit and may pose risks. However, the certainty of neither a benefit nor a risk has been proven yet in large-scale human intervention trials.
Good sources of flavonoids include all citrus fruits, berries, ginkgo Biloba, onions (particularly red onion, parsley, pulses, tea (especially white tea, and green tea), red wine, seabuckthorn, and dark chocolate (with a cocoa content of seventy percent or greater).
Flavonoid Benefits
Flavonoids are becoming very popular because they have many health-promoting effects including anti-allergic, anti-cancer, antioxidant, anti-inflammatory, and anti-viral properties. Recent studies have shown that flavonoids prevent the oxidation of low-density lipoprotein thereby reducing the risk for the development of atherosclerosis.
Foods that contain high amounts of flavonoids include blueberries, red beans, cranberries, and blackberries. Many other foods, including red and yellow fruits and vegetables and some nuts, also contain flavonoids. Red wine and certain teas also are rich in flavonoids.
Citrus
A variety of flavonoids are found in citrus fruits, including grapefruit. The citrus bioflavonoids include hesperidin (a glycoside of the flavanone hesperetin), quercitrin, rutin (two glycosides of the flavonol quercetin), and the flavone tangeritin. In addition to possessing in vitro antioxidant activity and an ability to increase intracellular levels of vitamin C, rutin and hesperidin may have beneficial effects on capillary permeability and blood flow. They also exhibit anti-allergy and anti-inflammatory benefits of quercetin from in vitro studies. Quercetin can also inhibit reverse transcriptase, part of the replication process of retroviruses. The therapeutic relevance of this inhibition has not been established. Hydroxyethylrutosides (HER) have potential for use in the treatment of abnormal capillary permeability, bruising, hemorrhoids, and varicose veins.
Garlic, Leeks and Onions
Quercetin is the key flavonoid in this family of vegetables. Known for its ability to spark the immune system into action, quercetin is rapidly taking its place at the top of the antioxidant pyramid.
Black, Green and White Tea
All members of the tea family are packed with a special group of flavonoids known as flavonols (catechin, epicatechin, epigallocatechin, epicatechin gallate). Research has shown that these powerful flavonoids work directly on replicating DNA sequences to prevent mutations that lead to cancer initiation. Drink 2 to 4 cups of freshly brewed tea daily.
Quercetin
A flavonoid and more specifically a flavonol is the aglycone form of other flavonoid glycosides, such as rutin and quercitrin, found in citrus fruit, buckwheat, and onions. Quercetin forms the glycosides, quercitrin, and rutin, together with rhamnose and rutinose, respectively. Although there is preliminary evidence that asthma, lung cancer, and breast cancer are lower among people consuming higher dietary levels of quercetin, the U.S. Food and Drug Administration (FDA), EFSA, and the American Cancer Society have concluded that no physiological role exists. The American Cancer Society states that dietary quercetin "is unlikely to cause any major problems or benefits."
Blueberries, Acai Berries and Grapes
Humans have been eating berries and grapes since early in our history. The flavonoids in these foods have been shown to help our immune system attack and destroy rogue cancer cells before they have a chance to develop and become malignant.
Epicatechin (EC)
May improve blood flow and has potential for cardiac health. Cocoa, the major ingredient of dark chocolate, contains relatively high amounts of epicatechin and has been found to have nearly twice the antioxidant content of red wine and up to three times that of green tea in vitro. It appears the potential antioxidant effects in vivo are minimal as the antioxidants are rapidly excreted from the body. Flavonoids exist naturally in cacao, but because they can be bitter, they are often removed from chocolate, even dark chocolate. Although flavonoids are present in milk chocolate, milk may interfere with their absorption.
Other Sources of Flavonoids
Other dietary flavonoid sources are beans, spinach, buckwheat, strawberry, blueberries, and rooibos plant. The concentration and composition of flavonoids in plants may vary depending on the growing condition, maturity, plant part, and variety. Soy flavonoids are also used to ease menopausal symptoms.
Author Credentials: Ian was born and grew up in Australia. Since then, he has traveled and lived in numerous locations and currently resides in Montreal, Canada. Ian is the founder, a writer, and editor in chief for Disabled World. Ian believes in the Social Model of Disability, a belief developed by disabled people in the 1970s. The social model changes the focus away from people's impairments and towards removing barriers that disabled people face daily. To learn more about Ian's background, expertise, and achievements, check out his bio.