Human studies on the absorption, distribution, metabolism, and excretion of tea polyphenols

Clifford, M.N., Van Der Hooft, J.J. and Crozier, A. (2013) Human studies on the absorption, distribution, metabolism, and excretion of tea polyphenols. American Journal of Clinical Nutrition, 98(6), 1619S-1630S. (doi: 10.3945/ajcn.113.058958)

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Abstract

Recent research on the bioavailability of flavan-3-ols after ingestion of green tea by humans is reviewed. Glucuronide, sulfate, and methyl metabolites of (epi)catechin and (epi)gallocatechin glucuronide reach peak nanomolar per liter plasma concentrations 1.6−2.3 h after intake, indicating absorption in the small intestine. The concentrations then decline, and only trace amounts remain 8 h after ingestion. Urinary excretion of metabolites over a 24-h period after green tea consumption corresponded to 28.5% of the ingested (epi)catechin and 11.4% of (epi)gallocatechin, suggesting higher absorption than that of most other flavonoids. The fate of (−)-epicatechin-3-O-gallate, the main flavan-3-ol in green tea, is unclear because it appears unmetabolized in low concentrations in plasma but is not excreted in urine. Possible enterohepatic recirculation of flavan-3-ols is discussed along with the impact of dose and other food components on flavan-3-ol bioavailability. Approximately two-thirds of the ingested flavan-3-ols pass from the small to the large intestine where the action of the microbiota results in their conversion to C-6−C-5 phenylvalerolactones and phenylvaleric acids, which undergo side-chain shortening to produce C-6−C-1 phenolic and aromatic acids that enter the bloodstream and are excreted in urine in amounts equivalent to 36% of flavan-3-ol intake. Some of these colon-derived catabolites may have a role in vivo in the potential protective effects of tea consumption. Although black tea, which contains theaflavins and thearubigins, is widely consumed in the Western world, there is surprisingly little research on the absorption and metabolism of these compounds after ingestion and their potential impact on health.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Crozier, Professor Alan and Van Der Hooft, Mr Justin
Authors: Clifford, M.N., Van Der Hooft, J.J., and Crozier, A.
College/School:College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Journal Name:American Journal of Clinical Nutrition
ISSN:0002-9165
ISSN (Online):1938-3207

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