Dose-response plasma appearance of green tea catechins in adults

SCOPE: Tea is an infusion of the Camellia sinensis leaves. The most prevalent bioactive compounds in green tea are catechins (C), which are of great interest for their potential health-promoting effects. However, metabolism and bioavailability of C are not fully understood. METHODS AND RESULTS: This study investigates the human bioavailability (plasma appearance) of C after drinking three doses of infused green tea in a randomized cross-over design. The sum of area under the curve increased between the small (0.75% w/v, 180 mg total C) and medium (1.25%) dose of ingested green tea but not between the medium and the high (1.75%) dose. The overall pattern for the sum of C did not reflect the fate of individual C. While (-)-epigallocatechin and 4'-O-Me-epigallocatechin showed saturation in plasma between the medium and high green tea doses, (-)-epigallocatechin gallate and (-)-epicatechin did not "saturate" and increased proportionally with the ingested dose. Regardless of the dose, C appeared rapidly in plasma as monophasic curves, suggesting absorption in the small intestine and minimal entero-hepatic circulation. CONCLUSION: As a conclusion, when studying dose response of polyphenols and metabolites, one must look not only at the overall pattern of plasma appearance, but also at data specific for each metabolite.