Effects of regular ingestion of black tea on haemostasis and cell adhesionmolecules in humans

Objective: To assess the effects in humans of regular ingestion of black te a on haemostasis-related variables and cell adhesion molecules. Design: Twenty-two subjects were recruited from the general population to a randomised-controlled crossover study. Subjects stopped drinking tea, apar t from that provided, for the duration of the study. During a 4-week baseli ne period all subjects drank 5 cups/day (250 ml) of hot water. The effects of 5 cups/day of black tea for 4 weeks were then compared with hot water. P latelet aggregation in response to three doses of collagen and ADP, plasma concentrations of coagulation and fibrinolytic factors (fibrinogen, factor VII, tPA, PAI-1) and plasma concentrations of cell adhesion molecules (solu ble P-selectin, E-selectin, ICAM-1, VCAM-1) were assessed twice, one week a part, at the end of each period. Twenty-four hour urinary concentration of 4-O-methylgallic acid (4OMGA), assessed once at the end of each period, was used as a marker of black tea polyphenol intake. Results: The 24 It urinary excretion of 4OMGA was increased during regular ingestion of black tea in comparison to hot water (P<0.0001). Black tea res ulted in lower soluble P-selectin (P= 0.01) in comparison to hot water, but did not influence other adhesion molecules. Soluble P-selectin was signifi cantly correlated with mean collagen-stimulated platelet aggregation at bas eline (r=0.61, P=0.003), and during regular ingestion of hot water (r=0.70, P<0.0001) and black tea (r=0.51, P=0.01). However, platelet aggregation wa s not different between the black tea and hot water periods for collagen- o r ADP-stimulated aggregation at any dose. Coagulation and fibrinolytic fact ors were also not different between periods. Conclusions: The effect of black tea on soluble P-selectin provides a poten tial mechanism for cardiovascular benefits of regular ingestion of tea.