Effects of tea intake on blood pressure: a meta-analysis of randomised controlled trials.

Abstract

The effect of tea intake on blood pressure (BP) is controversial. We performed a meta-analysis of randomised controlled trials to determine the changes in systolic and diastolic BP due to the intake of black and green tea. A systematic search was conducted in MEDLINE, EMBASE and the Cochrane Controlled Trials Register up to May 2014. The weighted mean difference was calculated for net changes in systolic and diastolic BP using fixed-effects or random-effects models. Previously defined subgroup analyses were performed to explore the influence of study characteristics. A total of twenty-five eligible studies with 1476 subjects were selected. The acute intake of tea had no effects on systolic and diastolic BP. However, after long-term tea intake, the pooled mean systolic and diastolic BP were lower by -1·8 (95% CI -2·4, -1·1) and -1·4 (95% CI -2·2, -0·6)mmHg, respectively. When stratified by type of tea, green tea significantly reduced systolic BP by 2·1 (95% CI -2·9, -1·2)mmHg and decreased diastolic BP by 1·7 (95% CI -2·9, -0·5)mmHg, and black tea showed a reduction in systolic BP of 1·4 (95% CI -2·4, -0·4)mmHg and a decrease in diastolic BP of 1·1 (95% CI -1·9, -0·2)mmHg. The subgroup analyses showed that the BP-lowering effect was apparent in subjects who consumed tea more than 12 weeks (systolic BP -2·6 (95% CI -3·5, -1·7)mmHg and diastolic BP -2·2 (95% CI -3·0, -1·3)mmHg, both P<0·001). The present findings suggest that long-term (≥12 weeks) ingestion of tea could result in a significant reduction in systolic and diastolic BP.