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

Abstract

To assess the effects in humans of regular ingestion of black tea on haemostasis-related variables and cell adhesion molecules. Twenty-two subjects were recruited from the general population to a randomised-controlled crossover study. Subjects stopped drinking tea, apart from that provided, for the duration of the study. During a 4-week baseline 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. Platelet 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 (soluble P-selectin, E-selectin, ICAM-1, VCAM-1) were assessed twice, one week apart, 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. The 24 h urinary excretion of 4OMGA was increased during regular ingestion of black tea in comparison to hot water (P<0.0001). Black tea resulted in lower soluble P-selectin (P=0.01) in comparison to hot water, but did not influence other adhesion molecules. Soluble P-selectin was significantly correlated with mean collagen-stimulated platelet aggregation at baseline (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 was not different between the black tea and hot water periods for collagen- or ADP-stimulated aggregation at any dose. Coagulation and fibrinolytic factors were also not different between periods. The effect of black tea on soluble P-selectin provides a potential mechanism for cardiovascular benefits of regular ingestion of tea. This study was supported by grants from the Tea Trade Health Research Association and the National Heart Foundation of Australia.