title: The effect of black tea on blood pressure: a systematic review with meta-analysis of randomized controlled trials.
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.
authors: Unilever Research & Development Vlaardingen, Vlaardingen, The Netherlands; Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors: Arno
authors: A
authors: Greyling
authors: Unilever Research & Development Vlaardingen, Vlaardingen, The Netherlands.
authors: Rouyanne T
authors: RT
authors: Ras
authors: Unilever Research & Development Vlaardingen, Vlaardingen, The Netherlands; Top Institute Food and Nutrition, Wageningen, The Netherlands.
authors: Peter L
authors: PL
authors: Zock
authors: Department of Cardiology and Angiology, Campus Mitte, Charité - Universitätsmedizin, Berlin, Germany; DZHK (German Centre for Cardiovascular Research), Berlin, Germany.
authors: Mario
authors: M
authors: Lorenz
authors: Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors: Maria T
authors: MT
authors: Hopman
authors: Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom.
authors: Dick H J
authors: DH
authors: Thijssen
authors: Unilever Research & Development Vlaardingen, Vlaardingen, The Netherlands.
authors: Richard
authors: R
authors: Draijer
mesh_terms: D001794:Blood Pressure; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D013662:Tea
chemical_list: D013662:Tea