These results suggest that green tea and Rooibos tea may have cardiovascular effects through inhibition of ACE activity.

PMID: 

Public Health Nutr. 2010 May ;13(5):730-7. Epub 2010 Feb 10. PMID: 20144258

Abstract Title: 

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

Abstract: 

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

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