Effects of green tea, black tea and Rooibos tea on angiotensin-converting enzyme and nitric oxide in healthy volunteers

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 close 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 ACEII 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.