Multiple effects of probiotics on different types of diabetes: a systematic review and meta-analysis of randomized, placebo-controlled trials

Background: A systematic review and meta-analysis was designed to evaluate the effect of probiotics on diabetes and its associated risk factors. Methods: We systematically searched the Cochrane Library, PubMed, EMBASE and Web of Science to June 2016. We also hand-searched the citation lists of included studies and previously identified systematic reviews to identify further relevant trials. Our primary outcome variables included glucose, glycated hemoglobin ( HbA(1c)) and insulin. The pooled standardized mean difference was used to compare the effect between the probiotics and controlled groups, and the pooled standardized mean difference effect size with a 95% confidence interval (CI) was estimated using a random- effect model. Heterogeneity was assessed with Cochran's Q and Higgins I-2 tests. Two reviewers assessed trial quality and extracted data independently. The analysis and bias for each included study was performed and assessed using Review Manager 5.2. Results: Eighteen randomized, placebo-controlled studies (n = 1056 participants, 527 consuming probiotics, 529 not consuming probiotics) were included for analysis. Comparing the probiotics groups with the control groups, there were statistically significant pooled standardized mean differences on the reduction of glucose (-0.61, 95% CI -0.98, - 0.24; p = 0.001), insulin (-0.49, 95% CI -0.93, - 0.04; p = 0.03) and HbA(1c) (-0.39, 95% CI -0.60, -0.19%; p = 0.0001). Subgroup analysis also indicated statistical significance on the reduction of low-density lipoprotein cholesterol (LDL-C) in non-type 2 diabetes (non-T2DM) mellitus patients with diabetes, for the pooled standardized mean difference was -0.29 (95% CI -0.54, -0.04; p = 0.02). Conclusions: Probiotics may have beneficial effects on the reduction of glucose, insulin and HbA(1c) for diabetes, especially for T2DM mellitus patients.