Effects of green tea consumption on glycemic control: a systematic review and meta-analysis of randomized controlled trials

Abstract

Background

The results of human clinical trials investigating the effects of green tea on glycemic control are inconsistent.

Methods

We conducted a systematic review and meta-analysis of RCTs that examined the effects of green tea supplementation on glycemic control. A literature search in PubMed, Embase, and Cochrane Library databases for RCTs that investigated the effect of green tea consumption on glycemic control was performed up to February 2020. A random-effects model was used to estimate weighted mean difference (WMD) with 95% confidence intervals (CIs).

Results

Twenty-seven trials involving 2194 subjects were included in the meta-analysis. The pooled results showed that green tea significantly lowered fasting blood glucose by − 1.44 mg/dL (95%CI:-2.26, − 0.62 mg/dL; P < 0.001) with no obvious heterogeneity (I² = 7.7%). However, green tea consumption did not significantly affect fasting insulin and HbA1c values. The mean differences were − 0.46μIU/mL (95% CI: − 1.10, 0.17μIU/mL; P = 0.21) for fasting insulin and − 0.06%; (95% CI: − 0.12, 0.01%; P = 0.07) for HbA_1c concentrations. Heterogeneity was significant in fasting insulin (I² = 46.8%) and mild in HbA_1c (I² = 1.7%).

Conclusions

In short-term trials, green tea supplementation significantly reduced fasting glucose, but had no significant effect on fasting insulin and HbA_1c. Long-term trials assessing the effects of green tea supplementation on glycemic control are needed.