Green tea and blood pressure effects

Many different dietary supplements are marketed, but the evidence for effectiveness is mixed. Green tea is one of the most common beverages. Green tea extracts are thought to possess antioxidant and ACE-inhibitor properties. Green tea polyphenols also inhibit the absorption of lipids from the intestines and facilitate the conversion of cholesterol into bile acids. Epidemiologic studies have shown that green tea has a cardioprotective effect and evidence synthesis has shown that consumption of green tea is associated with blood vessel relaxation.

To evaluate the effect of green tea consumption on blood pressure and lipid profile, we appraised and synthesized the evidence from clinical trials evaluating the effect of green tea on blood pressure and lipid profile. We searched five electronic databases and included only double-blinded randomised clinical trials (RCTs). We also assessed the reporting quality of included studies.

We identified 38 eligible studies, out of which we included 20 RCTs with over 1,500 participants. Overall, the studies were of moderate quality. Meta-analysis showed that green tea consumption caused a significant reduction in systolic blood pressure and total and LDL cholesterol. The effects on diastolic blood pressure, HDL cholesterol, and triglycerides were not significant. We also observed that the maximum effects of green tea occurred when the daily intake of epigalocatechin-3-gallate (the most abundant and bioactive compound in green tea extracts) was approximately 200 mg which equates to 5-6 cups of tea daily. Above this dosage, adverse events appeared to be more frequent and more severe.

Impact

Daily consumption of 5-6 cups of green tea could result in reductions in systolic blood pressure, total cholesterol, and LDL cholesterol. Green tea should not be recommended as a substitute for current management of patients with established hypertension or dyslipidaemia. Green tea appears to be well tolerated, but consumption in high doses may be associated with adverse events. There is uncertainty about the effects of prolonged green tea intake; therefore, longer-term independent clinical trials warranted.

Publications

• The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials.  Onakpoya I, Spencer E, Heneghan C, Thompson M. NMCD http://dx.doi.org/10.1016/j.numecd.2014.01.016

Associated media 

WorldHealth.Net –  Green Tea Supports Heart Health.
Nutraingredients-usa.com – Green tea may offer blood pressure and cholesterol benefits, but too early for recommendations, says meta-analysis.