Consumption of Green Tea Causes Rapid Increase in Plasma Antioxidant Power in Humans

Abstract

Green tea contains polyphenolic antioxidants that have shown anticarcinogenic properties in animal and in vitro experimental studies. Current data regarding absorption and bioavailability of tea antioxidants in humans, however, are conflicting. In this study, plasma and urine antioxidant power after ingestion of green tea was measured using the ferric reducing/antioxidant power (FRAP) assay (US patent pending) to assess absorption, systemic distribution, and renal excretion of green tea antioxidants in healthy adults. Results showed that absorption of green tea antioxidants was rapid, with peak increase in plasma FRAP of around 4% at 40 minutes after ingestion: mean increase was 44 ± 9 (SE) mmol/l. Excretion of polyphenolic antioxidants was also fast, peaking at 60-90 minutes, with significant correlation between urinary FRAP values and urinary total phenolic concentrations (r = 0.845, p < 0.001). In control studies, no increase in plasma or urine FRAP values was seen after intake of water. Although the amount of antioxidants absorbed was relatively small and the increase in plasma antioxidant power was of short duration, results demonstrate that some potentially anticarcinogenic polyphenolic antioxidants in green tea enter the systemic circulation soon after ingestion and cause a significant increase in plasma antioxidant status. This increase may, in turn, lower oxidative damage to DNA and so decrease risk of cancer.