Objective: The object of this study was to investigate the in vivo antioxidant effect of green tea and dosage effect of green tea on antioxidant effect.

Design: We tested 10 healthy subjects (aged 23-25 y, five women and five men) with overnight fasting. The total antioxidant capacity of plasma was measured at baseline and 60 min and 120 min after ingestion of 150 ml green tea. Green tea was prepared by infusing 2.5 g of dried green tea leaves for 2 min at 80 degrees C in 150 ml of water. In the second week, they took 300 ml of tea (5.0 g of green tea leaves) and, in the third week, 450 ml of tea (7.5 g of green tea leaves). The total antioxidant capacities of plasma were determined with a Total Antioxidant Kit (Randox Laboratories Ltd, UK) using a Cobas Mira analyser (Roche Diagnostic Systems Inc., Switzerland). The mean intra-assay coefficient of variation was 1.2%.

Results: The total antioxidant capacity of plasma increased by 1.1% at 60 min and 2.1% at 120 min over baseline value in subjects consuming 150 ml of green tea, which was statistically not significant. However, total antioxidant capacity of plasma after consuming 300 ml of green tea showed a significant increase of 7.0% after 60 min and 6.2% after 120 min (P<0.0001), and after consuming 450 ml 12.0% after 60 min and 12.7% after 120 min over baseline value (P<0.0001).

Conclusions: Total antioxidant capacity of plasma was significantly increased after taking green tea in amounts of 300 and 450 ml. A positive increment according to green tea dosage was also observed.

Sponsorship: This work was funded by the Pacific Corporation (Korea).