Plasma and lipoprotein levels of tea catechins following repeated tea consumption

Epidemiological studies suggest that antioxidant flavonoids in tea may redu ce the risk of cardiovascular disease, possibly via protection of low-densi ty lipoproteins (LDL) against oxidation. However, the extent of absorption of tea flavonoids and their accumulation in LDL during regular consumption of tea is not clear. Therefore we investigated plasma and lipoprotein level s of catechins during tea consumption and the impact on LDL oxidizability e x vivo. Eighteen healthy adults consumed, in an incomplete balanced cross-o ver design, green tea, black tea, black tea with milk or water, one cup eve ry 2 hr (eight cups/day) for three days. Blood samples were obtained in the mornings and evenings of each day. Plasma total catechin concentration was determined in all blood samples, and the distribution of catechins among l ipoproteins was determined at the end of the third day (t = 60 hr), The res istance of LDL to copper-induced oxidation ex vivo was assessed before tea consumption and at t = 60 hr. Repeated tea consumption during the day rapid ly increased plasma total catechin levels whereas they declined overnight w hen no tea was consumed. There was a gradual increase in plasma levels in t he mornings (respectively, 0.08 mu M vs, 0.20 mu M on first and last day of black tea consumption) and evenings (respectively, 0.29 mu M vs. 0.34 mu M on first and last day of black tea consumption). Green tea catechins were mainly found in the protein-rich fraction of plasma (60%) and in high-densi ty lipoproteins (23%), Although present in LDL, the concentration of catech ins in LDL was not sufficient to enhance the resistance of LDL to oxidation ex vivo. Addition of milk to black tea did not affect any of the parameter s measured. In conclusion, the present study shows that catechin levels in blood rapidly increase upon repeated tea consumption, The accumulation of c atechins in LDL particles is not sufficient to improve the intrinsic resist ance of LDL to oxidation ex vivo.