Effects of tea or tea extract on metabolic profiles in patients with type 2 diabetes mellitus: a meta-analysis of ten randomized controlled trials.

As consumption of tea has been confirmed as a protective factor for type 2 diabetes mellitus (T2DM), it would be interesting to know if T2DM patients could benefit from tea. Because of small sample sizes and inconsistent results of previous studies, we performed this meta-analysis to reevaluate the effects of tea or tea extract on all available outcomes in patients with T2DM. We systematically searched electronic databases of PubMed, Cochrane Library and EMBASE to identify randomized controlled trials of tea in T2DM patients up to January 2015. Weight mean differences for the changes in all outcomes were pooled by Review Manager 5.2 (Cochrane Collaboration, Oxford, England). A total of ten trials including 608 subjects were identified. The meta-analysis found that tea could alleviate the decrease of fasting blood insulin [1.30 U/L, 95% CI (0.36, 2.24)], and reduced waist circumference only in more than 8-week intervention [-2.70 cm, 95% CI (-4.72, -0.69)], whereas there were no statistically significant differences with regard to homeostasis model of insulin resistance 0.38 (-0.18, 0.95), fasting blood glucose -0.05 mmol/L (-0.51, 0.40), low density lipoprotein-cholesterol 0.07 mmol/L (-0.15, 0.29), high density lipoprotein-cholesterol 0.01 mmol/L (-0.08, 0.09), body mass index -0.15 kg/m(2) (-0.50, 0.21), SBP 0.35 mmHg (-3.54, 4.24), DBP -1.02 mmHg (-3.53, 1.48), triglycerides -0.11 mmol/L (-0.28, 0.05) and fasting cholesterol -0.05 mmol/L (-0.20, 0.11) in patients with T2DM, and leptin, ADPN, CRE and UA were also non-significant. The intervention of tea or tea extraction could maintain a stable fasting blood insulin and reduce waist circumference in the T2DM patients; however, the effects on other outcomes were not significant. Copyright © 2015 John Wiley & Sons, Ltd.