The effect of black tea on blood pressure: a systematic review with meta-analysis of randomized controlled trials.

OBJECTIVE: Epidemiological evidence has linked consumption of black tea, produced from Camellia sinensis, with a reduced risk of cardiovascular diseases. However, intervention studies on the effects of tea consumption on blood pressure (BP) have reported inconsistent results. Our objective was to conduct a systematic literature review with meta-analysis of controlled human intervention studies examining the effect of tea consumption on BP. METHODS: We systematically searched Medline, Biosis, Chemical Abstracts and EMBASE databases through July 2013. For inclusion, studies had to meet the following pre-defined criteria: 1) placebo controlled design in human adults, 2) minimum of 1 week black tea consumption as the sole intervention, 3) reported effects on systolic BP (SBP) or diastolic BP (DBP) or both. A random effects model was used to calculate the pooled overall effect of black tea on BP. RESULTS: Eleven studies (12 intervention arms, 378 subjects, dose of 4-5 cups of tea) met our inclusion criteria. The pooled mean effect of regular tea ingestion was -1.8 mmHg (95% CI: -2.8, -0.7; P = 0.0013) for SBP and -1.3 mmHg (95% CI: -1.8, -0.8; P<0.0001) for DBP. In covariate analyses, we found that the method of tea preparation (tea extract powders versus leaf tea), baseline SBP and DBP, and the quality score of the study affected the effect size of the tea intervention (all P<0.05). No evidence of publication bias could be detected. CONCLUSIONS: Our meta-analysis indicates that regular consumption of black tea can reduce BP. Although the effect is small, such effects could be important for cardiovascular health at population level.