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

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 (I-2 = 7.7%). However, green tea consumption did not significantly affect fasting insulin and HbA1c values. The mean differences were - 0.46 mu IU/mL (95% CI: - 1.10, 0.17 mu IU/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 (I-2 = 46.8%) and mild in HbA(1c)(I-2 = 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.