The relation between single/double or repeated tea catechin ingestions and plasma antioxidant activity in humans

Objective: The purpose of this study was to investigate the effects of single/double or repeated intake of a normal amount of tea catechin on plasma catechin concentrations and antioxidant activity in young women. Design: First, after an overnight fast, five healthy subjects were given water or single/double dose(s) of tea polyphenol extract (164 mg tea catechins containing 61% epigallocatechin gallate in 190 ml water). Blood samples were taken before and 30, 60 and 180 min after the ingestion. Second, 16 healthy subjects ingested the tea polyphenol extract three times a day at mealtimes for 7 days followed by withdrawal of tea polyphenol extract for 7 days. Blood samples were taken before and after ingestion, and 7 days after the withdrawal of tea catechin. Subjects were prohibited from drinking any beverages containing polyphenols or antioxidant supplements during the study period. Catechin and other antioxidant concentrations in the plasma were measured, and changes in antioxidant activity were evaluated by ferric reducing ability of plasma assay. Results: Single/double ingestion of tea polyphenol extract did not cause an increase in the antioxidant activity. There was no also change in antioxidant activity after the ingestion of tea polyphenol extract for 7 days. Plasma-free epigallocatechin gallate concentration remained at the pre-study level; however, the plasma FRAP value decreased significantly at 7 days after the withdrawal of tea polyphenol extract. Decreases in endogenous antioxidants in the plasma, including vitamin C and bilirubin, were also observed 7 days after withdrawal of tea polyphenol. Conclusions: The results suggest that continuous daily intake of tea catechins affects the concentrations of endogenous antioxidants in the plasma and has the potential to maintain total antioxidant activity.