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Diabetes Metab J. 2017 Aug;41(4):251-262. doi: 10.4093/dmj.2017.41.4.251.

The Effectiveness of Green Tea or Green Tea Extract on Insulin Resistance and Glycemic Control in Type 2 Diabetes Mellitus: A Meta-Analysis.

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Division of Medicine, School of life and Medical Science, University College London, London, UK.
Centre for Population Health Sciences, University of Edinburgh, Edinburgh, UK.
NIHR Bristol Biomedical Research Centre, Nutrition Theme, University of Bristol, Bristol, UK.
Centre for Exercise, Nutrition and Health Sciences, School for Policy Studies, University of Bristol, Bristol, UK.


Green tea or green tea extract (GT/GTE) has been demonstrated to reduce insulin resistance and improve glycemic control. However, evidence for this health beneficial effect is inconsistent. This systematic review evaluated the effect of GT/GTE on insulin resistance and glycemic control in people with pre-diabetes/type 2 diabetes mellitus (T2DM). Ovid MEDLINE, Embase, AMED, Web of Science, and the Cochrane Library were searched up to April 2017 for randomised controlled trials of participants with pre-diabetes or T2DM, where the intervention was GT/GTE. Meta-analysis was performed to assess the standardised mean difference (SMD) in biomarkers of insulin resistance and glycemic control between GT/GTE and placebo groups. Six studies (n=382) were pooled into random-effects meta-analysis. Overall, no differences were found between GT/GTE and the placebo for glycosylated hemoglobin (HbA1c: SMD, -0.32; 95% confidence interval [CI], -0.86 to 0.23), homeostatic model assessment for insulin resistance (HOMA-IR: SMD, 0.10; 95% CI, -0.17 to 0.38), fasting insulin (SMD, -0.25; 95% CI, -0.64 to 0.15), and fasting glucose (SMD, -0.10; 95% CI, -0.50 to 0.30). No evidence support the consumption of GT/GTE could reduce the levels of HbA1c, HOMA-IR, fasting insulin, or fasting glucose in people with pre-diabetes/T2DM. However, the studies included were small and of varying quality.


Diabetes mellitus, type 2; Glycemic control; Green tea; Insulin resistance; Meta-analysis

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No potential conflict of interest relevant to this article was reported.

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