Acute effects of ingestion of black tea on postprandial platelet aggregation in human subjects

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Abstract
Results of population studies suggest that black tea can reduce cardiovascular risk. Effects of black-tea polyphenols to reduce platelet aggregability may help to explain any benefits. Given that black tea is often consumed with and after meals, and man spends much of his life in the postprandial state, the objective of the present study was to investigate the acute effects of ingestion of black tea on postprandial platelet aggregation ex vivo. Twenty healthy participants had platelet aggregation and blood lipids assessed before and 4 h after the ingestion of 50 g dairy fat on two occasions in random order, corresponding to black tea or hot water. Black tea or hot water (one cup) was consumed immediately following the dairy fat, then after 1·5 and 3·0 h. Platelet aggregation ex vivo was assessed in platelet-rich plasma in response to three concentrations of collagen (0·2, 0·6, 2·0 μg/ml) and ADP (2, 4, 8 μM). Urinary concentrations of 4-O-methylgallic acid were used as an indicator that tea polyphenols were absorbed. Serum total cholesterol and triacylglycerol concentrations increased significantly 4 h after ingesting the dairy fat, but there was no significant difference between black tea and hot-water treatments on the cholesterol or triacylglycerol responses. Urinary 4-O-methylgallic acid concentrations were significantly increased following ingestion of black tea (P=0·0001) but not water. Black tea in comparison to hot water did not inhibit collagen or ADP-induced postprandial platelet aggregation. The results of this study do not support the suggestion that reduced postprandial platelet aggregability contributes to any benefits of black tea on cardiovascular risk.