The effects of melatonin supplementation on blood pressure in patients with metabolic disorders: a systematic review and meta-analysis of randomized controlled trials.

The current systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted to evaluate the potential effect of melatonin supplementation on blood pressure in patients with metabolic disorders. The following databases were searched until June 2018: PubMed, MEDLINE, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials. Two reviewers independently assessed the eligibility of retrieved studies, extracted data from included trials, and evaluated the risk of bias of included studies. Statistical heterogeneity was tested using Cochran's Q test and I-square (I2) statistic. Data were pooled using random-effect models and standardized mean difference (SMD) was considered as the effect size. Eight RCTs, out of 743 potential citations, were eligible to be included in the current meta-analysis. The pooled findings indicated a significant reduction in systolic (SBP) (SMD = -0.87; 95% CI, -1.36, -0.38; P = 0.001; I2: 84.3) and diastolic blood pressure (DBP) (SMD = -0.85; 95% CI, -1.20, -0.51; P = 0.001; I2: 68.7) following melatonin supplementation in individuals with metabolic disorders. In summary, the current meta-analysis demonstrated that melatonin supplementation significantly decreased SBP and DBP in patients with metabolic disorders. Additional prospective studies are recommended using higher supplementation doses and longer intervention periods to confirm our findings.