The six major subclasses of flavonoid include:
Anthocyanidins (e.g., cyanidin, pelargonidin)
Catechins or flavanols (e.g., epicatechin, gallocatechin)
Flavones (e.g., apigenin, luteolin and chrysin)
Flavonols (e.g., kaempferol, myricetin, quercetin)
Flavanones (e.g., hesperidin, naringenin)
Isoflavones (e.g., genistein, daidzein).

Potential uses of flavonoid substances
These are a large family of plant secondary metabolites, principally recognized for their health-promoting properties in human diets. Most flavonoids outperform well-known antioxidants, such as ascorbate (vitamin C) and alpha-tocopherol (vitamin E), in in vitro antioxidant assays because of their strong capacity to donate electrons or hydrogen atoms.

Anti-inflammatory
Most flavonoid agents have anti-inflammatory properties.

Asthma benefit
Asthma symptoms may be reduced with a diet high in these beneficial phytonutrients.

Brain health
If your diet has plenty of flavonoids, you are likely helping maintain a healthy brain in old age and lowering your risk for heart disease. Flavonoids are potent antioxidants found in plant-based foods from red wine to tea to vegetables. Dr. Luc Letenneur of INSERM in Bordeaux, France, followed a group of 1,640 older, dementia-free individuals for 10 years, recording information on their diet at the beginning of the study. The men and women who took in the most flavonoids showed significantly better mental performance at the beginning of the study, even after the researchers adjusted the data for the influence of sex, level of education, and age. And those who ranked in the top half for flavonoid consumption showed more favorable progress in their cognitive function over time; for example, after 10 years, men and women in the lowest fourth for flavonoid consumption had lost 2.1 points on a test of cognitive function known as the Mini-Mental State Examination, compared to a 1.2-point loss for the people in the highest fourth for flavonoid intake.

Immune system
Most flavonoid molecules have anti-germ activity.

Anti-tumor
Most flavonoid substances have anti-cancer properties.

Anti-oxidant
Flavonoid molecules are powerful antioxidants. Extracts from onion and various flavonoids induce the cellular antioxidant system. Onion extract and quercetin were able to increase the intracellular concentration of glutathione by approximately 50%.

Heart health
Researchers at Johns Hopkins University in Baltimore, MD tested dark chocolate on platelet activity, C-reactive protein and lipid profile in healthy volunteers. For one week the volunteers ate dark chocolate (providing 700 mg of flavonoids per day). After a week of regular dark chocolate consumption, LDL cholesterol fell by 6% and HDL cholesterol rose by 9%. Dark chocolate reduced blood levels of CRP.

Vasodilation and nitric oxide production
Diets rich in either red wine, quercetin or catechin induce endothelium-dependent vasorelaxation in rat aorta in a resting state through the enhancement of (*)NO production, without modifying O(2)(.-) generation, thus the bioavailability of (*)NO was increased. The increase in the (*)NO-cyclic GMP pathway explains the beneficial effect of flavonoids at vascular level.

Venous insufficiency
Beta-aescin is found in horse chestnut herb,.

Flavonoid compounds protect against heart disease, stroke
Epidemiological evidence suggests an inverse relationship between dietary intake of flavonoids and cardiovascular risk. The biological activities of flavonoids are partly related to their antioxidative effects.
   Accumulated evidence from experimental and epidemiological studies indicates that there is a low risk of degenerative diseases, cardiovascular disease, hypertension, cataract, stroke and, in particular, cancers in people with a high intake of fruit and vegetables. This protective effect is assumed to be associated mainly with the antioxidant activities of either individual or interacting bioactive components present in the fruits and vegetables, and with other biochemical and physical characteristics of the identified and unknown bioactive components. The implicated bioactive components present in citrus fruits include vitamin C, beta-carotene, flavonoids, limonoids, folic acid, and dietary fibre. A high intake of citrus fruits may reduce the risk of degenerative diseases.

Foods rich in flavonoids -- from apples and pears to dark chocolate and red wine -- may help shield postmenopausal women from coronary heart disease, cardiovascular disease and stroke, a new study shows. Flavonoids have been hypothesized to protect the heart by reducing levels of low-density lipoprotein or "bad" cholesterol and reducing inflammation. Dr. Pamela J. Mink of Exponent, Inc., used three newly available databases from the U.S. Department of Agriculture to determine the flavonoid contain of foods, the researchers analyzed results of food questionnaires on diet from 34,489 postmenopausal women participating in the Iowa Women's Health Study. Dr. Pamela J. Mink and colleagues specifically examined the association between the amount of flavonoids the diet and heart disease and death over a 16-year period. The new information allowed the researchers to look at both total flavonoids and seven different subclasses of the plant compound. Three subclasses of flavonoids, anthocyanidins, flavanones, and flavones, were linked to a significantly reduced risk of heart disease, blood vessel disease or cardiovascular disease mortality. Specific foods also were linked to risk reductions in heart, blood vessel disease and mortality as well, including bran, apples, pears, red wine, grapefruit, strawberries and chocolate. American Journal of Clinical Nutrition, March 2007.

Absorption and antioxidant activity
Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence, or epiphenomenon?
Free Radic Biol Med. 2006. Lotito SB, Frei B. Linus Pauling Institute, Oregon State University, 571 Weniger Hall, Corvallis, OR 97331, USA.
The beneficial health effects of fruits and vegetables have been attributed, in part, to antioxidant flavonoids present in these foods. Large, transient increases in the total antioxidant capacity of plasma have often been observed after the consumption of flavonoid-rich foods by humans. These observations led to the hypothesis that dietary flavonoids play a significant role as antioxidants in vivo, thereby reducing chronic disease risk. This notion, however, has been challenged recently by studies on the bioavailability of flavonoids, which indicate that they reach only very low concentrations in human plasma after the consumption of flavonoid-rich foods. In addition, most flavonoids are extensively metabolized in vivo, which can affect their antioxidant capacity. Furthermore, fruits and vegetables contain many macro- and micronutrients, in addition to flavonoids, that may directly or through their metabolism affect the total antioxidant capacity of plasma. The large increase in plasma total antioxidant capacity observed after the consumption of flavonoid-rich foods is not caused by the flavonoids themselves, but is likely the consequence of increased uric acid levels.

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