| Abstract: |
The inhibitory activity of tea against tumorigenesis has been demonstrated in many animal models and has been suggested by some epidemiological studies. Such activity has generally been attributed to tea catechins. To understand the bioavailability of tea catechins in humans, we gave 18 individuals different amounts of green tea and measured the time- dependent plasma concentrations and urinary excretion of tea catechins. After taking 1.5, 3.0, and 4.5 g of decaffeinated green tea solids (dissolved in 500 ml of water), the maximum plasma concentration (C(max)) of (-)- epigallocatechin-3-gallate (EGCG) was 326 ng/ml, the C(max) of (-)- epigallocatechin (EGC) was 550 ng/ml, and the C(max) of (-)-epicatechin (EC) was 190 ng/ml. These C(max) values were observed at 1.4-2.4 h after ingestion of the tea preparation. When the dosage was increased from 1.5 to 3.0 g, the C(max) values increased 2.7-3.4-fold, but increasing the dose to 4.5 g did not increase the C(max) values significantly, which suggested a saturation phenomenon. The half-life of EGCG (5.0-5.5 h) seemed to be higher than the half-life of EGC or EC (2.5-3.4 h). EGC and EC, but not EGCG, were excreted in the urine. Over 90% of the total urinary EGC and EC was excreted within 8 h. When the tea dosage was increased, the amount of EGC and EC excretion seemed to increase, but a clear dose-response relationship was not observed. The present study provides basic pharmacokinetic parameters of green tea catechins in humans; these parameters may be used to estimate the levels of these compounds after drinking tea. |
