Flavonoids: Types, Food Sources, and Health Benefits

Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2011/02/14 - Updated: 2025/05/25
Publication Type: Informative
Category Topic: Antioxidants and Carotenoids - Academic Publications

Page Content: Synopsis - Introduction - Main - Insights, Updates

Synopsis: This information provides a comprehensive overview of flavonoids - plant-derived compounds also known as bioflavonoids or Vitamin P - and their presence in a wide range of fruits, vegetables, teas, and other foods. Flavonoids are highlighted for their potent antioxidant, anti-inflammatory, and anti-cancer properties, with research suggesting they may help reduce the risk of several chronic diseases, including certain cancers, cardiovascular disease, and atherosclerosis. The article draws on both scientific studies and expert commentary, making it a useful resource for individuals interested in dietary approaches to health maintenance, particularly seniors and people with disabilities who may benefit from the protective effects of flavonoid-rich foods.

The detailed breakdown of food sources - such as berries, citrus, onions, teas, and dark chocolate - along with discussion of specific flavonoids like quercetin and epicatechin, offers practical guidance for incorporating these nutrients into daily diets. The information is authoritative due to the author's expertise in health and disability advocacy, as well as references to published scientific research, making it especially helpful for those seeking accessible, evidence-based dietary advice - Disabled World (DW).

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 Content

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.

Insights, Analysis, and Developments

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.