Effects of green tea, black tea and rooibos on angiotensin-converting enzyme activity in healthy volunteers

Epidemiological studies show that tea drinkers exhibit lower risk for developing cardiovascular diseases. However, the pharmacological mechanism behind this effect is unknown.

Previous studies in vitro have shown inhibition of angiotensin-converting enzyme (ACE) by green and black tea [1]. The aim of this project was to investigate the effect of Camellia sinensis L., green tea (Japanese Sencha), black tea (Indian Assam B.O.P.) and Aspalathus linearis Dahlg., Rooibos tea on ACE activity after oral intake. Seventeen healthy volunteers received a single oral dose of 400ml green tea, black tea or Rooibos tea in a randomized three-phase cross over study. ACE activity was measured (at 0, 30, 60 and 180 minutes) in all three phases. ACE activity was analysed with a commercial radioenzymatic assay. In addition, ACE genotype was determined using a PCR method. After oral intake of a single dose of Rooibos tea a significant inhibition of ACE activity, p<0.01 after 30min and p<0.05 after 60min was seen. A significant inhibition of ACE activity was also seen with the green tea for the genotype II p<0.05, 30 minutes after intake of the tea and for the genotype ID p<0.05, 60 minutes after intake. A significant inhibition of ACE activity was also seen with the Rooibos tea for the genotype II p<0.05, 60 minutes after intake.

In conclusion, intake of green tea and Rooibos tea significantly inhibit ACE activity and may affect blood pressure regulation and thereby prevent cardiovascular diseases.

Reference: [1] Persson, I.A-L. et al. (2006)J. Parm. Pharmacol. 58:1139–1144.