a1 Department of Medical and Health Sciences, Division of Drug Research/Pharmacology, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden
a2 Department of Medical and Health Sciences, Division of Drug Research/Clinical Pharmacology, Faculty of Health Sciences, Linköping University, Linköping, Sweden
Objective Tea has been reported to reduce cardiovascular mortality, but the underlying mechanisms are largely unknown. The aim of the current project was to investigate the effect of green tea (Japanese Sencha), black tea (Indian Assam B.O.P.) and Rooibos tea (South Africa) on angiotensin-converting enzyme (ACE) and nitric oxide (NO).
Design Seventeen healthy volunteers received a single oral dose of 400 ml green tea, black tea or Rooibos tea in a randomized, three-phase, crossover study. ACE activity and NO concentration were measured (at 0, 30, 60 and 180 min) in all phases. ACE activity was analysed by means of a commercial radioenzymatic assay. Nitrite was analysed as a marker of NO concentration. In addition, ACE genotype was determined using a PCR method.
Results Oral intake of a single dose of Rooibos tea significantly inhibited ACE activity after 30 min (P < 0·01) and after 60 min (P < 0·05). A significant inhibition of ACE activity was seen with green tea for the ACE II genotype 30 min after intake of the tea (P < 0·05) and for the ACE ID genotype 60 min after intake (P < 0·05). A significant inhibition of ACE activity was also seen with Rooibos tea for the ACE II genotype 60 min after intake (P < 0·05). No significant effect on NO concentration was seen.
Conclusions These results suggest that green tea and Rooibos tea may have cardiovascular effects through inhibition of ACE activity.
(Received May 19 2009)
(Accepted January 05 2010)
(Online publication February 10 2010)