Applied nutritional investigationBioavailability and catabolism of green tea flavan-3-ols in humans
Introduction
Green tea is one of the major dietary sources of polyphenols, catechins or flavan-3-ols being the main polyphenolic subclass present in tea leaves. Epidemiologic evidence is mounting describing the protective effects of green tea consumption against the risk of cardiovascular diseases and mortality. Moreover, specific mechanisms, such as vascular elasticity and protection against oxidative stress, have been extensively investigated and are good candidates to explain these protective effects [1], [2].
Bioavailability studies with green tea or green tea extracts have shown very different and controversial results [3], with urinary excretion ranging from unquantifiable traces to values close to 10% of the ingested amount [4], [5]. One study with only five volunteers, however, observed that two major phenolic catabolites, (−)-5-(3′,4′,5′-trihydroxyphenyl)-γ-valerolactone (M4) and (−)-5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (M6), accounted for up to 40% of the amount of ingested pure (−)-epigallocatechin (EGC) and (−)-epicatechin (EC) [6]. Similar differences could be observed when bioavailability studies were carried out with the second great source of flavan-3-ols, chocolate [3], [7], [8], or when single molecules, such as (−)-epigallocatechin-gallate (EGCG) or (+)-catechin, were introduced as supplements [9], [10].
These contrasting values present in the literature mainly derive from the complex catabolism that flavan-3-ols undergo within the human body, making it very difficult to recognize and quantify every single metabolite appearing in plasma and urine after green tea ingestion. Analytical constraints have drastically limited the identification and characterization of flavan-3-ol catabolites in the past [11], and the lack of synthesized pure standards have significantly decreased the quality of their quantification. However, with all the health benefits attributed to green tea intake, it is now necessary to define the absorption and catabolism of its bioactive components with greater clarity, with the help of more advanced analytical methodologies that are currently readily available in most research laboratories. Therefore, in this study we used high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) to investigate green tea flavan-3-ol catabolism and plasma pharmacokinetic and urinary excretion with the aim of estimating the bioavailability of these molecules in detail by taking into account all known and some unknown catabolites deriving from their interaction with several loci within the gastrointestinal tract.
Section snippets
Tea and chemicals
Two-hundred–milliliter bottles of ready-to-drink (RTD) green tea beverage were supplied by Soremartec Italia S.r.l. (Alba, CN, Italy). This product represents 1.4% of the Italian market of RTD tea and 21.6% of the Italian market of RTD green tea (Iri Infoscan, May 2008/May 2009) [12]. The product was industrially made from Sri Lanka tea leaves. The manufacturing process was based on infusion in hot water, which reproduces the traditional tea preparation. The RTD tea is composed of a tea
Analysis of tea
The flavan-3-ol contents of 400 mL of RTD green tea (n = 12, each sample coming from a different pack, all packs from the same lot) were 106.2 ± 3.9 μmol (mean ± standard deviation) of (−)-epigallocatechin 164.4 ± 5.5 μmol of (−)-epigallocatechin-3-gallate, 39.6 ± 1.7 μmol of (−)-epicatechin, 48.9 ± 1.7 μmol of (−)-epicatechin-3-gallate, 19.5 ± 1.3 μmol of (+)-gallocatechin, 9.8 ± 0.9 μmol of (+)-catechin, and 15.5 ± 0.6 μmol of (+)-gallocatechin-3-gallate, making a total of 403.9 ± 9.4 μmol of total
Discussion
The consumption of RTD teas, generally called “iced tea,” is increasing in Western countries and is often overtaking the intake of traditional hot tea [12]. Considering the evidence that tea is one of the most significant sources of polyphenols in the human diet and that tea consumption [16] and polyphenol intake in general [17] are strongly related to reduced risk for several chronic diseases, the aim of our investigation was to assess the actual exposure of human volunteers to the most
Conclusion
This study demonstrates that green tea catechins are more bioavailable than previously observed when colonic ring fission metabolites are taken into consideration (39% of the amount ingested). Regular consumption of RTD green tea containing flavan-3-ols allows a non-marginal exposition of the human body to their catabolites, somehow justifying the numerous beneficial actions described as linked to green tea intake.
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This study was supported by a research grant from Soremartec Sp.A., Alba, Italy.