Effect of acute and chronic tea consumption on platelet aggregation in patients with coronary artery disease

Epidemiological studies suggest that tea consumption is associated with a d ecreased risk of cardiovascular events, but the mechanisms of benefit remai n undefined. Platelet aggregation is a precipitating event in cardiovascula r disease, and tea contains antioxidant flavonoids that are known to decrea se platelet aggregation in vitro. To test the effect of tea consumption on platelet aggregation, we randomized 49 patients with coronary artery diseas e to either 450 mt of black tea or water consumed initially, followed by 90 0 mt of tea or water daily for 4 weeks in a crossover design. Ex vivo plate let aggregation in platelet-rich plasma was assessed in response to ADP and thrombin receptor-activating peptide at baseline and 2 hours and 4 weeks a fter beverage consumption. We observed dose-dependent platelet aggregation in response to each agonist, and neither relation was altered by acute or c hronic tea consumption. Plasma flavonoids increased with acute and chronic tea consumption, indicating adequate absorption of tea flavonoids. In concl usion. these results demonstrate that acute and chronic black tea consumpti on does not affect ex vivo platelet aggregation in patients with coronary a rtery disease. These findings suggest that an effect of tea flavonoids on p latelet aggregation is unlikely to be the explanation for the reduction in risk of cardiovascular events noted in epidemiological studies.