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      Bioavailability of the Polyphenols: Status and Controversies

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          Abstract

          The current interest in polyphenols has been driven primarily by epidemiological studies. However, to establish conclusive evidence for the effectiveness of dietary polyphenols in disease prevention, it is useful to better define the bioavailability of the polyphenols, so that their biological activity can be evaluated. The bioavailability appears to differ greatly among the various phenolic compounds, and the most abundant ones in our diet are not necessarily those that have the best bioavailability profile. In the present review, we focus on the factors influencing the bioavailability of the polyphenols. Moreover, a critical overview on the difficulties and the controversies of the studies on the bioavailability is discussed.

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          Most cited references 128

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          Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies.

          Polyphenols are abundant micronutrients in our diet, and evidence for their role in the prevention of degenerative diseases is emerging. Bioavailability differs greatly from one polyphenol to another, so that the most abundant polyphenols in our diet are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Mean values for the maximal plasma concentration, the time to reach the maximal plasma concentration, the area under the plasma concentration-time curve, the elimination half-life, and the relative urinary excretion were calculated for 18 major polyphenols. We used data from 97 studies that investigated the kinetics and extent of polyphenol absorption among adults, after ingestion of a single dose of polyphenol provided as pure compound, plant extract, or whole food/beverage. The metabolites present in blood, resulting from digestive and hepatic activity, usually differ from the native compounds. The nature of the known metabolites is described when data are available. The plasma concentrations of total metabolites ranged from 0 to 4 mumol/L with an intake of 50 mg aglycone equivalents, and the relative urinary excretion ranged from 0.3% to 43% of the ingested dose, depending on the polyphenol. Gallic acid and isoflavones are the most well-absorbed polyphenols, followed by catechins, flavanones, and quercetin glucosides, but with different kinetics. 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. These data may be useful for the design and interpretation of intervention studies investigating the health effects of polyphenols.
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            Flavonoid intake and long-term risk of coronary heart disease and cancer in the seven countries study.

            To determine whether flavonoid intake explains differences in mortality rates from chronic diseases between populations. Cross-cultural correlation study. Sixteen cohorts of the Seven Countries Study in whom flavonoid intake at baseline around 1960 was estimated by flavonoid analysis of equivalent food composites that represented the average diet in the cohorts. Mortality from coronary heart disease, cancer (various sites), and all causes in the 16 cohorts after 25 years of follow-up. Average intake of antioxidant flavonoids was inversely associated with mortality from coronary heart disease and explained about 25% of the variance in coronary heart disease rates in the 16 cohorts. In multivariate analysis, intake of saturated fat (73%; P = 0.0001), flavonoid intake (8%, P = .01), and percentage of smokers per cohort (9%; P = .03) explained together, independent of intake of alcohol and antioxidant vitamins, 90% of the variance in coronary heart disease rates. Flavonoid intake was not independently associated with mortality from other causes. Average flavonoid intake may partly contribute to differences in coronary heart disease mortality across populations, but it does not seem to be an important determinant of cancer mortality.
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              Dietary flavonoid and isoflavone glycosides are hydrolysed by the lactase site of lactase phlorizin hydrolase.

              Lactase phlorizin hydrolase (LPH; EC 3.2.1.62) is a membrane-bound, family 1 beta-glycosidase found on the brush border of the mammalian small intestine. LPH, purified from sheep small intestine, was capable of hydrolysing a range of flavonol and isoflavone glycosides. The catalytic efficiency (k(cat)/K(m)) for the hydrolysis of quercetin-4'-glucoside, quercetin-3-glucoside, genistein-7-glucoside and daidzein-7-glucoside was 170, 137, 77 and 14 (mM(-1) s(-1)) respectively. The majority of the activity occurred at the lactase and not phlorizin hydrolase site. The ability of LPH to deglycosylate dietary (iso)flavonoid glycosides suggests a possible role for this enzyme in the metabolism of these biologically active compounds.
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                Author and article information

                Journal
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                Molecular Diversity Preservation International (MDPI)
                1422-0067
                31 March 2010
                2010
                : 11
                : 4
                : 1321-1342
                Affiliations
                Department of Veterinary Public Health and Food Safety, Italian National Institute of Health, Viale Regina Elena 299, 00161 Rome, Italy; E-Mails: carmelina.filesi@ 123456iss.it (C.F.); rosaria.vari@ 123456iss.it (R.V.); beatrice.scazzocchio@ 123456iss.it (B.S.); roberta.masella@ 123456iss.it (R.M.)
                Author notes
                [* ] Author to whom correspondence should be addressed; E-Mail: maxdar@ 123456iss.it ; Tel.: +39-6-4990-2763; Fax: +39-6-49387-101.
                Article
                ijms-11-01321
                10.3390/ijms11041321
                2871118
                20480022
                © 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.

                This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                Categories
                Review

                Molecular biology

                dietary polyphenols, bioavailability, metabolites

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