Polyphenols can be classified into the following categories:
Polyphenols occur in all plant foods and contribute to the beneficial health effects of vegetables and fruit. Their contribution to the antioxidant capacity of the human diet is much larger than that of vitamins. The total intake of polyphenols in a person's diet could amount to 1 gram a day, whereas combined intakes of beta-carotene, vitamin C, and vitamin E from food most often  is about 100 mg a day.
   Phenolic acids account for about one third of the total intake of polyphenols in our diet, and flavonoids account for the remaining two thirds. Flavonoids are further subdivided into several categories.
    Phenolic acids are simple molecules such as caffeic acid, vanillin, and courmaric acid. Phenolic acids form a diverse group that includes the widely distributed hydroxybenzoic and hydroxycinnamic acids. Phenolic acid compounds seem to be universally distributed in plants. They have been the subject of a great number of chemical, biological, agricultural, and medical studies. Hydroxycinnamic acid compounds (p-coumaric, caffeic acid, ferulic acid) occur most frequently as simple esters with hydroxy carboxylic acids or glucose, while the hydroxybenzoic acid compounds (p-hydroxybenzoic, gallic acid, ellagic acid) are present mainly in the form of glucosides. Ellagic acid is found in Pomegranate. Furthermore, phenolic acids may occur in food plants as esters or glycosides conjugated with other natural compounds such as flavonoids, alcohols, hydroxyfatty acids, sterols, and glucosides. Coffee is particularly rich in bound phenolic acids, such as caffeic acid, ferulic acid, and p-coumaric acid. Phenolic acids found in blueberries include gallic acid, p-hydroxybenzoic acid, coffeic acid, p-coumaric acid and vanillic acid.
    Flavonoids -- Flavonoids are a subclass of polyphenols. Flavonoids are widely distributed in nature, albeit not uniformly. As a result, specific groups of foods are often rich sources of one or more subclasses of these polyphenols. The polyphenolic structure of flavonoids and tannins renders them quite sensitive to oxidative enzymes and cooking conditions.
            Anthocyanins  and anthocyanidins are a large water-soluble pigment group found in a large number of fruits, vegetables and flowers. particularly grapes, Grape-Seed extract, and berries. These pigments give plants their brilliant colors ranging from pink through scarlet, purple and blue. Bilberry and other berries have a high concentration of anthocyanins. Scientists have identified more than 500 different anthocyanins including cyanidin, pelargonidin, delphinidin, malvidin, and paeonidin.
            Catechins or Flavanols -- are found found in tea. Grape seeds have the monomeric flavan-3-ols catechin, epicatechin, gallocatechin, epigallocatechin, and epicatechin 3-O-gallate. Research shows that the cocoa bean is rich in specific antioxidants, with the basic structure of catechins and epicatechin, and especially the polymers procyanidins,
            Flavanols -- catechin and epicatechin
            Flavones -- Apigenin, Luteolin. The herb Chamomile has a good amount of apigenin.
            Flavonols --  are found at high concentrations in onions, apples, red wine, broccoli, tea, and Ginkgo-Biloba. The most common in the American diet are Quercetin (70%), Kaempferol (16%), and Myricetin (6%). Flavonols also include fisetin, isoquercitrin and hyperoside.
            Flavanones -- Hesperidin, Naringin
            Isoflavones -- Genistein, Daidzein are found in soy and have an influence on bone health among postmenopausal women, together with some weak hormonal effects. Isoflavones are selectively incorporated in certain tissues like the breast and ovaries. They are able to bind to the estrogen receptors alpha (ER-alpha) and beta (ER-beta). However, the binding affinity for Genistein to ER-alpha is only 4%, the affinity to ER-beta is 87% compared to 17beta-estradiol. Thus, depending on the estradiol concentration, they exhibit weak estrogenic or antiestrogenic activity. Isoflavones can influence transcription and cell proliferation. They modulate enzyme activities as well as signal transduction, and have antioxidant properties. Epidemiological studies have shown that the prevalence of hot flashes is lower in women from countries with high dietary isoflavone intake such as Japan than in Western nations with low isoflavone intake. Isoflavones are colorless.
            Lignans found in nuts and whole grain cereals. Flaxseed has a high content of lignan.
            Proanthocyanidins --  found in grapes, red wine, pine bark. Pycnogenol is a pine bark extract. Grape seed extract provides a concentrated source of polyphenols, many of which are proanthocyanidins. Red wine is rich in the complex polyphenols, the proanthocyanidins. Proanthocyanidins share common properties with other polyphenols, in particular their reducing capacity and ability to chelate metal ions. However, their polymeric nature clearly makes them different. They have a high affinity for proteins and their absorption through the gut barrier is likely limited to the molecules of low polymerization degree and to the metabolites formed by the colonic microflora, as suggested by in vitro experiments. The nutritional significance of proanthocyanidins is discussed in relation to their physico-chemical properties and bioavailability.
            Procyanidins (oligomeric catechins found at high concentrations in red wine, grapes and grape seeds, cocoa, Cranberry, apples, and some supplements such as Pycnogenol) have pronounced effects on the vascular system. Apples contain many kinds of polyphenols, and the main components are oligomeric procyanidins. Applephenon is apple polyphenol extract produced commercially from unripe apples, and has been used as food additive in order to prevent oxidation of components in foods.
            Stilbenes - Resveratrol is an exciting polyphenol which has been in the news a great deal for potential anti-cancer and anti-aging benefits. Resveratrol supplements are available for sale.
            Tannins  are found in red wine, tea, and nuts. They are large molecules. Many flavonoids in foods also occur as large molecules (tannins). These include condensed tannins (proanthocyanidins), derived tannins and hydrolysable tannins.

Absorption of Polyphenols
Gallic acid and isoflavones are the most well-absorbed polyphenols, followed by catechins, flavanones, and quercetin glucosides. The least well-absorbed polyphenols are the proanthocyanidins, the galloylated tea catechins, and the anthocyanins. Data are still too limited for assessment of hydroxycinnamic acids and other polyphenols.

Polyphenols in the Diet
Dietary polyphenols show a great diversity of structures, ranging from rather simple molecules (monomers and oligomers) to polymers. Higher-molecular-weight structures (with molecular weights of > 500) are usually designated as tannins, which refers to their ability to interact with proteins. Among them, condensed tannins (proanthocyanidins) are particularly important because of their wide distribution in plants and their contributions to major food qualities. There are a number of foods that have high polyphenol content, including my favorite, cacao.

Polyphenols in Wine
Red wine has polyphenol compounds such as anthocyanosides, catechins, proanthocyanidins, stilbenes and other phenolics.

Several studies have shown that a group of polyphenol antioxidant compounds found in grapes, green tea, soybeans and wine may lower the risk of a range of cancers, but exactly how these powerful compounds work has remained unclear.

Now, researchers report that plant-derived polyphenols can slow the growth of cancer cells in mice and curb the spread of cells by triggering a series or reactions that causes the cells to self-destruct, a process known as apoptosis.

Pycnogenol is a patented product obtained from the bark of French maritime pine. The primary ingredients are phenolic compounds such as catechin, epicatechin, and taxifoin, as well as flavonoids including procyanidins and proanthocyanidins.

Potential uses of polyphenols
Anti-inflammatory -- most have anti-inflammatory properties.
Immune system -- most have anti-microbial activity.
Anti-tumor -- most have anti-carcinogenicity properties.
Antioxidant -- 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%. Polyphenols may be helpful in diabetic retinopathy.
Heart -- A high intake of polyphenols is likely to have beneficial effects on the cardiovascular system. 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.

Dr. Sahelian's thoughts on Polyphenols
Polyphenols have been studied for several decades. At this time I believe enough research on polyphenols has been accumulated to begin taking advantage of these fascinating compounds in clinical use. A number of medical conditions could be prevented or improved with the use of polyphenols. These include circulatory disorders such as hypertension and coronary artery disease,, lung disorders such as asthma, cancers of various types, inflammatory conditions, certain liver conditions, diabetes, mood disorders, eye disorders such as cataracts, weak eyesight due to aging, and macular degeneration. We should consider polyphenols as compounds necessary for the various organs and tissues, and part of the countless substances necessary for proper functioning of this amazing organism we call the human body.

Polyphenol Research Update
Polyphenols and disease risk in epidemiologic studies.
Am J Clin Nutr. 2005 Jan;81(1):317S-25S.
Plant polyphenols, a large group of natural antioxidants, are serious candidates in explanations of the protective effects of vegetables and fruits against cancer and cardiovascular diseases. Epidemiologic studies are useful for evaluation of the human health effects of long-term exposure to physiologic concentrations of polyphenols, but reliable data on polyphenol contents of foods are still scarce. The aim of this review is to summarize available epidemiologic data on the health effects of polyphenols, focusing on the flavonoid subclasses of flavonols, flavones, catechins and on lignans.  Most studies to date have included only flavonols and flavones. With data becoming available for other polyphenols, these compounds should be included in future studies.

A blend of polyphenols explains the stimulatory effect of red wine on human endothelial NO synthase.
Nitric Oxide. 2005 Mar;12(2):97-104.
A high intake of polyphenols is likely to have beneficial effects on the cardiovascular system. Especially red wine is a rich source of polyphenols, and we have previously shown that French red wine upregulates eNOS, a protective enzyme in the cardiovascular system. The current study tested (poly)phenols of red wine for their ability to enhance eNOS expression. Of the polyphenols tested, we found 3,4',5-trihydroxy-trans-stilbene (trans-resveratrol) to be the most efficacious stimulator of eNOS expression (and eNOS transcription), but this compound alone could not explain the total stimulatory effect of red wine. The flavanols catechin and epicatechin, the flavonols fisetin, myricetin, isoquercitrin and hyperoside, the anthocyanins delphinidin, malvidin, and paeonidin, gallic acid, and the hydroxycinnamic acids ferulic acid and sinapinic acid did not change eNOS expression or eNOS promoter activity in any substantial way. The flavonol quercetin inhibited eNOS expression (with no effect on eNOS promoter activity). Cinnamic acid was a rather potent enhancer of eNOS expression, however with an efficacy of only 170%. Surprisingly, it reduced eNOS promoter activity. The anthocyanins cyanidin, the hydroxycinnamic acids p-coumaric acid and caffeic acid, and the phenolic acids benzoic acid and vanillic acid also enhanced eNOS expression moderately (with no effect on eNOS promoter activity). Thus, the increase in eNOS in response to red wine involves several polyphenolic compounds with a major contribution from trans-resveratrol and lesser contributions from cinnamic and hydroxycinnamic acids, cyanidin, and some phenolic acids.

Short-term administration of dark chocolate is followed by a significant increase in insulin sensitivity and a decrease in blood pressure in healthy persons.
Am J Clin Nutr. 2005 Mar;81(3):611-4.
Numerous studies indicate that flavanols may exert significant vascular protection because of their antioxidant properties and increased nitric oxide bioavailability. In turn, nitric oxide bioavailability deeply influences insulin-stimulated glucose uptake and vascular tone. Thus, flavanols may also exert positive metabolic and pressor effects. OBJECTIVE: The objective was to compare the effects of either dark or white chocolate bars on blood pressure and glucose and insulin responses to an oral-glucose-tolerance test in healthy subjects. After a 7-d cocoa-free run-in phase, 15 healthy subjects were randomly assigned to receive for 15 d either 100 g dark chocolate bars, which contained approximately 500 mg polyphenols, or 90 g white chocolate bars, which presumably contained no polyphenols. Successively, subjects entered a further cocoa-free washout phase of 7 d and then were crossed over to the other condition. Although within normal values, systolic blood pressure was lower after dark than after white chocolate ingestion. Dark, but not white, chocolate decreases blood pressure and improves insulin sensitivity in healthy persons.

Comprehensive study on vitamin C equivalent antioxidant capacity (VCEAC) of various polyphenols in scavenging a free radical and its structural relationship.
Crit Rev Food Sci Nutr. 2004;44(4):253-73.
Department of Food Science and Technology, Cornell University, Geneva, New York
Antioxidant capacity for a wide range of natural or synthetic polyphenols was comprehensively evaluated by vitamin C equivalent antioxidant capacity (VCEAC) assay. The polyphenols tested are grouped into the following categories: vitamins (beta-carotene, alpha-tocopherol, vitamin A, and vitamin C), phenolic acids (benzoic acid, phenylacetic acid, cinnamic acid, and their derivatives), flavonoids (anthocyanidin, flavanol, chalcone, flavanone, flavone, flavonol, isoflavone, and their derivatives), synthetic food additives (BHA, BHT, TBHQ, and PG), and other miscellaneous polyphenols (ellagic acid, sesamol, eugenol, thymol, etc.). A positive linear relationship between VCEAC and the number of free OH groups around the flavonoid framework was found, whereas, for phenolic acids, the linear relationship was not as good as with the flavonoid aglycones. Groups of chemicals having comparable structures generally showed similar trends. Polyphenols commonly showed a higher VCEAC compared to monophenolics. Compounds like gallic acid with 3 vicinal hydroxy substitutions on the aromatic ring in phenolic acids or like epigallocatechin with 3 vicinal hydroxy substitutions on the B ring in flavonoids showed the highest antioxidant capcity among the groups. In the flavonoids, 2 characteristic chemical structures were very important, the catechol moiety in the B ring and the 3-OH functional group in a chroman ring. Glycosylated flavonoids showed less potent antioxidant capacity than their aglycone alone. Synthetic antioxidant food additives (BHA, TBHQ, and BHT) conventionally used in the food industry were less effective antioxidants than ascorbic acid. Other naturally occurring polyphenols tested followed the expected general trends of phenolic acids and flavonoids.

Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations.
Am J Clin Nutr. 2005 Jan;81(1 Suppl):284S-291S.
Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo.

Polyphenols and glutathione synthesis regulation.
Am J Clin Nutr. 2005 Jan;81(1 Suppl):277S-283S.
Polyphenols in food plants are a versatile group of phytochemicals with many potentially beneficial activities in terms of disease prevention. In vitro cell culture experiments have shown that polyphenols possess antioxidant properties, and it is thought that these activities account for disease-preventing effects of diets high in polyphenols. However, polyphenols may be regarded as xenobiotics by animal cells and are to some extent treated as such, ie, they interact with phase I and phase II enzyme systems. We recently showed that dietary plant polyphenols, namely, the flavonoids, modulate expression of an important enzyme in both cellular antioxidant defenses and detoxification of xenobiotics, ie, gamma-glutamylcysteine synthetase. This enzyme is rate limiting in the synthesis of the most important endogenous antioxidant in cells, glutathione. We showed in vitro that flavonoids increase expression of gamma-glutamylcysteine synthetase and, by using a unique transgenic reporter mouse strain, we showed increased expression in vivo, with a concomitant increase in the intracellular glutathione concentrations in muscles. Because glutathione is important in redox regulation of transcription factors and enzymes for signal transduction, our results suggest that polyphenol-mediated regulation of glutathione alters cellular processes. Evidently, glutathione is important in many diseases, and regulation of intracellular glutathione concentrations may be one mechanism by which diet influences disease development. The aim of this review is to discuss some of the mechanisms involved in the glutathione-mediated, endogenous, cellular antioxidant defense system, how its possible modulation by dietary polyphenols such as flavonoids may influence disease development, and how it can be studied with in vivo imaging.

Bioavailability and bioefficacy of polyphenols in humans. II. Review of 93 intervention studies.
Am J Clin Nutr. 2005 Jan;81(1 Suppl):243S-255S.
For some classes of dietary polyphenols, there are now sufficient intervention studies to indicate the type and magnitude of effects among humans in vivo, on the basis of short-term changes in biomarkers. Isoflavones (genistein and daidzein, found in soy) have significant effects on bone health among postmenopausal women, together with some weak hormonal effects. Monomeric catechins (found at especially high concentrations in tea) have effects on plasma antioxidant biomarkers and energy metabolism. Procyanidins (oligomeric catechins found at high concentrations in red wine, grapes, cocoa, cranberries, apples, and some supplements such as Pycnogenol) have pronounced effects on the vascular system, including but not limited to plasma antioxidant activity. Quercetin (the main representative of the flavonol class, found at high concentrations in onions, apples, red wine, broccoli, tea, and Ginkgo biloba) influences some carcinogenesis markers and has small effects on plasma antioxidant biomarkers in vivo, although some studies failed to find this effect. Compared with the effects of polyphenols in vitro, the effects in vivo, although significant, are more limited. The reasons for this are 1) lack of validated in vivo biomarkers, especially in the area of carcinogenesis; 2) lack of long-term studies; and 3) lack of understanding or consideration of bioavailability in the in vitro studies, which are subsequently used for the design of in vivo experiments. It is time to rethink the design of in vitro and in vivo studies, so that these issues are carefully considered. The length of human intervention studies should be increased, to more closely reflect the long-term dietary consumption of polyphenols.