Effects of green tea catechins with or without caffeine on glycemic control in adults: a meta-analysis of randomized controlled trials
Author: Xin-Xin Zheng, Yan-Lu Xu, Shao-Hua Li, Rutai Hui, Yong-Jian Wu, and Xiao-Hong Huang
Background: The effect of green tea catechins (GTCs) with or without caffeine on glycemic control is controversial. Objective: We aimed to identify and quantify the effects of GTCs or GTC-caffeine mixtures on glucose metabolism in adults. Design: A comprehensive literature search was conducted to identify relevant trials of GTCs with or without caffeine on markers of glycemic control [fasting blood glucose (FBG), fasting blood insulin (FBI), glycated hemoglobin (Hb A1c), and homeostatic model assessment of insulin resistance (HOMA-IR)]. Weighted mean differences were calculated for net changes by using fixed-effects models. Prespecified subgroup analyses were performed to explore the influence of covariates on net changes in FBG and FBI concentrations. Results: Twenty-two eligible randomized controlled trials with 1584 subjects were identified. Pooled analyses showed that FBG (−1.48 mg/dL; 95% CI: −2.57, −0.40 mg/dL) decreased significantly with GTCs with or without caffeine, whereas FBI (0.04 μU/mL; 95% CI: −0.36, 0.45 μU/mL), Hb A1c (−0.04%; 95% CI: −0.15, 0.08%), and HOMA-IR (−0.05; 95% CI: −0.37, 0.26) did not. Subgroup analyses indicated that the glucose-lowering effect was apparent when the duration of follow-up was over a median of 12 wk. Overall, no significant heterogeneity was detected for FBG, FBI, Hb A1c, or HOMA-IR. Conclusions: The meta-analysis showed that the administration of GTCs with or without caffeine resulted in a significant reduction in FBG. The limited data available on GTCs did not support a positive effect on FBI, Hb A1c, or HOMA-IR. Thus, more large and well-designed trials are needed in the future.