The results of studies investigating the effect of green tea on glucose control and insulin sensitivity in humans are inconsistent.
Researchers from the Chongqing Medical Nutrition Research Center, China, aimed to quantitatively evaluate the effect of green tea on glucose control and insulin sensitivity. The results were published on the American Journal of Clinical Nutrition.
Kai Liu at al. performed a strategic literature search of PubMed, EMBASE, and the Cochrane Library (updated to January 2013) for randomized controlled trials that evaluated the effects of green tea and green tea extract on glucose control and insulin sensitivity. Study quality was assessed by using the Jadad scale. Weighted mean differences were calculated for net changes in glycemic measures by using fixed-effects or random-effects models. They conducted prespecified subgroup and sensitivity analyses to explore potential heterogeneity. Meta-regression analyses were conducted to investigate dose effects of green tea on fasting glucose and insulin concentrations.
As a result, seventeen trials comprising a total of 1133 subjects were included in the current meta-analysis. Green tea consumption significantly reduced the fasting glucose and hemoglobin A1c (Hb A1c) concentrations by −0.09 mmol/L (95% CI: −0.15, −0.03 mmol/L; P < 0.01) and −0.30% (95% CI: −0.37, −0.22%; P < 0.01), respectively. Further stratified analyses from high Jadad score studies showed that green tea significantly reduced fasting insulin concentrations (−1.16 μIU/mL; 95%CI: −1.91, −0.40 μIU/mL; P = 0.03).
In conclusion, this meta-analysis suggested that green tea had favourable effects, ie, decreased fasting glucose and Hb A1c concentrations. Subgroup analyses showed a significant reduction in fasting insulin concentrations in trials with high Jadad scores.
