Effects of green tea catechins with or without caffeine on glycemic control in adults: a meta-analysis of randomized controlled trials

Am J Clin Nutr. 2013 Apr;97(4):750-62. doi: 10.3945/ajcn.111.032573. Epub 2013 Feb 20.

Abstract

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. This trial was registered at http://www.crd.york.ac.uk/prospero as CRD42012002139.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Blood Glucose / metabolism*
  • Caffeine / pharmacology*
  • Caffeine / therapeutic use
  • Camellia sinensis / chemistry*
  • Catechin / pharmacology*
  • Catechin / therapeutic use
  • Glycated Hemoglobin A / metabolism
  • Humans
  • Hyperglycemia / blood
  • Hyperglycemia / drug therapy
  • Hypoglycemic Agents / pharmacology*
  • Hypoglycemic Agents / therapeutic use
  • Insulin / blood*
  • Insulin Resistance
  • Metabolic Diseases / blood*
  • Phytotherapy
  • Plant Extracts / pharmacology
  • Plant Extracts / therapeutic use

Substances

  • Blood Glucose
  • Glycated Hemoglobin A
  • Hypoglycemic Agents
  • Insulin
  • Plant Extracts
  • Caffeine
  • Catechin