Flavonoid health effects

In conclusion, spectacular advances in the fields of flavonoid bioavailability and flavo-noid-mediated cell effects in relation to the development of new biological tools (e.g., proteomic analysis, reporter genes) have been achieved during the last decade. A more coherent picture of the ways flavonoids combine their redox properties and affinity to specific proteins is emerging. This wealth of new chemical and biological information suggests that the elucidation of in vivo molecular mechanisms and receptors involved in flavonoid health effects is at hand. 

HOLLMAN p c and KATAN M B (1997) Absorption, metabolism and health effects of dietary flavonoids in man , Biomed Pharmacother, 51, 305-10. 

Cyanidin is the most common anthocyanin in foods. In addition, anthocyanins are stabilized by the formation of complexes with other flavonoids (co-pigmentation). In the United States, the daily anthocyanin consumption is estimated at about 200 mg. Several promising studies have reported that consumption of anthocyanin-rich foods is associated with reductions of the risks of cancers - and atherosclerosis and with preventive effects against age-related neuronal and behavioral declines. These beneficial effects of anthocyanins might be related to their reported biological actions such as modulators of immune response and as antioxidants. Knowledge of anthocyanin bioavailability and metabolism is thus essential to better understand their positive health effects. 

Some of the bioactive phytochemicals found in fmits and vegetables are polyphenols, including flavonoids. This chapter provides a general overview of the relationship between flavonoids and health. The mechanisms of action believed to be behind the healthful effects of some compounds will also be mentioned. 

Hollman, P.C.H. and Katan, M.B., Dietary flavonoids intake, health effects and bioavailability. 

Proanthocyanidins are polymeric flavonoid compounds composed of flavan-3-ol subunits (Fig. II. 4.1), and are widely distributed in the plant kingdom, including plants that are important as a source of food (Santos-Buelga and Scalbert, 2000). They impart bitter and astringent properties. In addition, these compounds may have potential health effects (Santos-Buelga and Scalbert, 2000). 

As flavonoids are ubiquitous components of fruits and vegetables, they are part of almost any human diet. The identification of potential targets for the beneficial health effects of flavonoids exponentially increased over the years. The physiological relevance of the interactions of flavonoids with cell... 

Despite the apparently beneficial health effects of flavonoids, several studies indicate their mutagenicity and genotoxicity in mammalian systems. This may be due to their activity as pro-... 

Recently, anthocyanins have received less attention compared to other flavonoids despite their far-reaching health effects. Because berries might have occupied such a large part of early diets, our ancestors probably ate more anthocyanins when compared to our food intake. In fact, according to some researchers, we might be deficient in anthocyanins. When people understand the antioxidant potential of the phytochemicals, perhaps we could improve the deficiencies by taking them. In due-course, our daily common foods may give even more enjoyment to us. 

The impact of plant products on the metabolism of synthetic dmgs results from the inhibition or activation of cytochrome P-450 (CYP) enzymes. Evaluation of the potential activation of CYP by administration of natural plant products or dietary supplements is important for prediction of interactions between their components and dmgs. Therefore, attention is directed to research on the impact of products available on the food market known as natural non-nutritive substances on dmg absorption. Non-nutritive dietary components are mainly secondary plant metabolites, which include, among others, phenolic compounds such as phenolic acids and flavonoids. The health effects of non-nutritive substances are not yet known. So far, there is no answer on the extent to which they are absorbed and metabolized by the body, and there is no information on the permitted daily intake for these compounds. This information is particularly important because certain non-nutritive natural substances are simultaneously considered to be anti-nutritional factors, mainly because they inhibit digestion and reduce the bioavailability of nutrients or dmgs. It is also possible that they form undesirable interactions with dmgs. The positive health effects of non-nutritive natural substances are not only attributed to their antioxidant properties. These substances are involved in various metabolic... 

Numerous health benefits have been reported or claimed for flavonoids and isoflavones, such as in cancer prevention, cardiovascular effects, and relief of menopausal syndromes. However, concerns have been raised about potential adverse effects, such as enhancement of reproductive organs and anti-thyroid effects. In order to evaluate potential beneficial or hazardous health effects from flavonoids. 

In the following, a few theories that have recently received considerable attention as being explanatory to some of the putative health effects of flavonoids are presented. 

The renewed interest in flavonoids as health-benefiting compounds creates the necessity to search for their exact function in the human body. From a health point of view, the main interest at present is concentrated on the ability of the flavonoids to act as free radical scavengers. Methodologies for the assessment of these and other functions are currently being developed. These in vitro methods clearly demonstrate that flavonoids are effective in scavenging various types of free radicals, in inhibiting lipid oxidation and the activity of certain enzymes as well as in possessing antiviral effects. 

Flavonoids as antioxidants have been reviewed several times 45s including an outline of many claims to their beneficial health effects . Due to their complex structures and different classes (eight thousand different compounds are known ), researchers often resorted to qualitative screening methods to evaluate their antioxidant potentials in mixed aqueous/lipid phases. For example, the so-called Trolox equivalent antioxidant capacity (TEAC), the concentration of Trolox with equivalent antioxidant activity of a 1 mM concentration of the substrate, is frequently used in heterogeneous systems. Unfortunately, this can be an unreliable measure of the activity of the substance, especially if initiation is also carried out in the aqueous phase. Nevertheless, there have been some efforts made to evaluate antioxidant activities of specific flavonoids using more quantitative methods in heterogeneous systems in order to mimic natural environments. A few examples are cited below to illustrate some approaches to determine flavonoid activities in micelles or lipid membranes. 

Creosote bush resin consists of phenolic (e.g., flavonoids and nordihydroguaiaretic acid), neutral (e.g., waxes), basic (e.g., alkaloids), and acidic (e.g., phenolic acids) compounds. The phenolic portion comprises 83-91% of the total resin. Nordihydroguaiaretic acid accounts for 5-10% of the dry weight of the leaves (Leonforte 1986). It is not known whether the health effects associated with creosote bush resin are attributable to the phenolic components. 

Hippuric acid was identified as a major metabolite associated with black tea consumption. " The compound l,3-dihydroxyphenyl-2-0-sulfate (sulfate conjugate of pyrogallol) was also identified as a black tea metabolite in humans. " Very low levels of theaflavins in plasma and urine were reported in humans after consumption of black tea. It was reported that the ingestion of either green tea or black tea results in a major increase in the excretion of hippuric acid into urine. The authors concluded that green tea and black tea consumption result in similar amounts of microbial degradation products that are absorbed by the body. They speculated that these microbial metabolites, not the native tea flavonoids, may be responsible for at least some of the health effects attributed to tea consumption. ... 

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