Polyphenols are a large class of chemical compounds synthesized by fruits, vegetables, teas, cocoa and other plants that possess certain health benefits. Polyphenols have antioxidnats, anti-inflammatory, anti-carcinogenic and other biological properties. Polyphenols are divided into several groups, one of which is flavenoids.
Polyphenols are extremely diverse. There is an amazing array of over 8,000 already-identified family members, one of the largest nutrient families known to scientists. Polyphenols are subdivided into several subclasses: phenolic acids, stilbenes, tannins, diferuloylmethanes and flavenoids. Some of the best-known flavonoids include quercetin, kaempferol, catechins, anthocyanins and anthocyanidins. This nutrient group is most famous for its antioxidant and anti-inflammatory health benefits, as well as its contribution of vibrant color to the foods we eat. The five basic categories of flavonoids are flavonols, flavan-3-ols, flavones, flavonones, and anthocyanidins.
Antioxidant Benefits
Because many flavonoids and especially those belonging to two subgroups called flavonols and flavan-3-ols, can be effective in reducing free radical damage to cells and other components in body tissue, they provide antioxidant benefits. Even though we do not know all the details about the way flavonoids function as antioxidants, however, studies have documented better protection of certain cell types, for example, red blood cells, following consumption of flavonoid-rich foods. In this antioxidant context, it is also worth pointing out the potentially unique relationship between flavonoids and vitamin C. Recent studies have shown the ability of flavonoids to alter transport of vitamin C, as well as to alter function of an enzyme called ascorbate oxidase, which converts vitamin C into a non-vitamin form (monodehydroascorbate). While we do not yet know the full meaning of these relationships, it is clear that the transport and cycling of vitamin C is flavonoid related. This association makes sense to us, since so many foods high in vitamin C are also high in flavonoids.
Anti-Inflammatory Benefits
Much of the research on flavonoids as anti-inflammatories has involved their ability to block the production of messaging molecules that promote inflammation. In metabolic terms, this activity of flavonoids involves the inhibition of cyclo-oxygenase (COX) and lipoxygenase(LOX) enzymes. Not only have specific flavonoids (for example, quercetin) been shown to provide these benefits but so also have flavonoid-containing extracts from a variety of foods, spices, and herbs. In addition to the metabolic activities described above, food flavonoids have also been shown to suppress inflammatory signaling in another metabolic pathway called the nuclear factor kappa-B (NF-kB) pathway.
Cardiovascular System Benefits
Not surprisingly, since many problems in the cardiovascular system involve problems with oxidative stress and inflammation, the antioxidant and anti-inflammatory benefits from food flavonoids provide direct support for this body system. In the bloodstream, flavonoids have been shown to help protect LDL cholesterol molecules from oxygen-related damage. This LDL protection, in turn, helps to lower risk of atherosclerosis. Flavonoids including rutin and hesperidin have also been shown to increase the strength and integrity of the blood vessel walls, lowering risk of blood vessel problems. In one study, adding a spice mix to a meal of beef—a mix that contained such flavonoid-rich herbs as oregano, rosemary, garlic, ginger, and black pepper—led to a significant improvement in vascular function over the next several hours. Yet herbs and spices are by no means the only foods studied in this regard; similar effects have been demonstrated for soy foods, chocolate, pomegranate juice, and grape juice. Also, numerous flavonoids, including quercetin and rutin, have been shown to help prevent excessive clumping together of platelet cells that could otherwise lead to unwanted clogging of the blood vessels. This property of flavonoids is called an "anti-aggregatory" property, and it's yet another way in which these phytonutrients help support the cardiovascular system.
Support of the Nervous System
Protection of nerve cells from oxygen-based damage, and help during the slow and demanding process of nerve regeneration (outside of the brain and spinal cord), are both demonstrated benefits of flavonoid intake for the nervous system. There is some preliminary evidence that the onset of certain chronic neurodegenerative diseases, including age-related dementia and Alzheimer's disease, may be delayed when long-term intake of flavonoids has been strong.
Because flavonoids may help to improve blood flow in the brain, there is also preliminary evidence to suggest the possibility of better brain functioning in some areas, including areas involving cognitive function.
Anti Cancer Potential
In terms of their anti-cancer potential, research on flavonoids has been somewhat mixed. Due to their well-documented antioxidant and anti-inflammatory properties, flavonoids would be expected to lower risk of certain cancers since chronic oxidative stress and chronic unwanted inflammation can place cells at greater risk of becoming cancerous. Furthermore, because flavonoids are known to modify the body's detoxification pathways, it might be expected that flavonoids would help lower exposure to unwanted toxins that could pose increased cancer risk. In studies on animals and on isolated cell types, the above expectations seem to be fully met, with flavonoid intake improving detoxification, oxidative stress, unwanted inflammation, and initiation of cells into pre-cancerous states. However, in larger scale studies on humans and risk of human cancers, greater intake of flavonoids has not been consistently associated with decreased risk of cancer. To date, the strongest evidence appears to involve breast cancer and lung cancer where decreased risk is a more consistent finding.