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Meta-Analysis
. 2014 Jul 31;9(7):e103247.
doi: 10.1371/journal.pone.0103247. eCollection 2014.

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

Arno Greyling  1 , Rouyanne T Ras  2 , Peter L Zock  3 , Mario Lorenz  4 , Maria T Hopman  5 , Dick H J Thijssen  6 , Richard Draijer  2
Affiliations
Meta-Analysis

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

Arno Greyling et al. PLoS One. .

Abstract

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.

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Conflict of interest statement

Competing Interests: The authors have read the journal's policy and have the following conflicts: AG, PLZ, RTR and RD are employed by Unilever R&D Vlaardingen. Unilever produces foods of which some are marketed to fit in a healthy diet and lifestyle. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials. No other authors declare a conflict of interest.

Figures

Figure 1
Figure 1. Flow diagram of the study selection procedure.
Figure 2
Figure 2. Net changes in SBP (A) and DBP (B) in randomized studies of black tea consumption.
Horizontal lines represent 95% confidence intervals. Grey diamonds represent the pooled estimates using fixed and random effects models respectively. Grassi et al. 2009 reported both office and ambulatory BP – both sets of data were included in the analyses, but to keep the weight of the study proportionate, the weight of each arm was halved.
Figure 3
Figure 3. Funnel plots of trials included in the meta-analysis for (A) systolic blood pressure and (B) diastolic blood pressure.
See this image and copyright information in PMC

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