Effects of metformin on blood pressure in nondiabetic patients: ameta-analysis of randomized controlled trials

Objective: To evaluate the effects of metformin on systolic blood pressure (SBP) and diastolic blood pressure (DBP) in nondiabetic patients. Methods: In this meta-analysis, we systematically searched PubMed, Embase, and the Cochrane Library through March 2016, and randomized controlled trials assessing the effects of metformin treatment compared with placebo were included. Random-effects models were used to estimate pooled mean differences in SBP and DBP. Results: Twenty-eight studies from 26 articles consisting of 4113 participants were included. Pooled results showed that metformin had a significant effect on SBP (mean difference -1.98mmHg; 95% confidence interval -3.61, -0.35; P = 0.02), but not on DBP (mean difference -0.67mmHg; 95% confidence interval -1.74, 0.41; P = 0.22). In subgroup analysis, we found that the effect of metformin on SBP was significant in patients with impaired glucose tolerance or obesity (BMI >= 30 kg/m(2)), with a mean reduction of 5.03 and 3.00 mmHg, respectively. Significant heterogeneity was found for both SBP (I-2 = 60.0%) and DBP (I-2 = 45.4%). A sensitivity analysis indicated that the pooled effects of metformin on SBP and DBP were robust to systematically dropping each trial. Furthermore, no evidence of significant publication bias from funnel plots or Egger's tests (P = 0.51 and 0.21 for SBP and DBP, respectively) was found. Conclusion: This meta-analysis suggested that metformin could effectively lower SBP in nondiabetic patients, especially in those with impaired glucose tolerance or obesity.