The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis

Objective: As a popular beverage, there has been much interest in studying the effects of tea intake on hypertension (HTN), a particular risk factor for cardiovascular disorders (CVDs). We have thus aimed to isolate the randomized controlled trials investigating the efficacy of black or green tea as a beverage in subjects with elevated blood pressure (BP), or HTN. Methods: PubMed, Scopus, Web of Science, and ProQuest dissertations and theses databases were searched from February 1, 1995, up to July 20, 2019, to identify relevant studies. Results: The search strategy generated 1119 trials, of which finally five trials fulfilled the criteria for being included in the current study. Three out of 5 articles showed a low risk of bias. According to nine measurements derived from 5 trials on 408 individuals, it was found that regular tea intake resulted in the reduction in SBP (weighted mean difference (WMD): -4.81 mmHg, 95 %CI: -8.40 to -1.58, P =.004) and DBP (WMD:-1.98 mmHg, 95 %CI: -3.77 to -0.20, P = .029); however, excluding the most heterogeneous trials showed that regular tea intake might reduce SBP and DBP by about -3.53 and -0.99 mmHg, respectively. Based on metaregression findings, we found the longer the duration of tea intake (>= 3 months), the higher the decrease in both SBP and DBP. Categorized studies, according to the tea type, revealed that the hypotensive effects of green tea were more pronounced compared to black tea. None of the studies reported any side effects. Conclusion: These results suggest the positive effects of regular tea intake on BP in subjects with elevated BP or HTN. Hence, it may be applicable to physicians, health care providers, and particularly HTN patients.