The effect of green tea on inflammatory mediators: A systematic review and meta-analysis of randomized clinical trials

Catechin in green tea might be able to reduce inflammatory mediators; therefore, in this study, we aimed to indicate green tea effects on inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), C-reactive protein (CRP), and interleukin-6 (IL-6). The advanced search methods of electronic databases were used to find randomized clinical trials that assessed green tea effect on inflammatory mediators among adult population. Google Scholar, PubMed/Medline, EMBASE, SCOPUS, and ISI Web of Science were searched until January 2019. Delphi checklist was used for assessing the quality of included articles. Mean changes in serum inflammatory biomarkers were calculated by subtracting endpoint values from the baseline in each study arm. Then the effect size for each selected study was estimated as the difference between mean changes in the intervention and control groups. We included 16 articles in our meta-analysis and 17 articles in systematic review. Our results indicated that green tea could not significantly decrease serum CRP levels and significantly increased IL-6 and significantly decreased TNF-alpha levels. In conclusion, green tea might not be able to change inflammatory mediators especially in diseases with low inflammation, but scientists who want to assess green tea effect on inflammatory mediators should perform their study on patients with high inflammation. Studies exclusive on male or female and considering nutrients intake as a confounding factor are a necessity.