Effect of Nigella sativa (black seed) supplementation on glycemic control: A systematic review and meta-analysis of clinical trials.

This study was aimed to quantify the antihyperglycemic effect of Nigella sativa (N. sativa). An in-depth search to identify clinical trials investigating the impact of N. sativa on glycemic indices via MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Library, and Google scholar databases were performed up to November 2018. We used a random effects model to estimate pooled effect size of fasting plasma glucose (FPG), postprandial blood glucose (PPBG), and hemoglobin A1c (HbA1c). A total of 17 randomized controlled trials investigating the effects of N. sativa on FPG, PPBG, and HbA1c were included. Meta-analysis suggested a significant association between N. sativa supplementation and reduction in FPG (weighted mean difference [WMD]: -9.93 mg/dl, 95% CI [-13.44, -6.41]), PPBG (WMD: -14.79 mg/dl, 95% CI [-24.19, -5.39]), and HbA1c (WMD: -0.57%, 95% CI [-0.77, -0.37]). Subgroup analysis revealed that N. sativa oil was more effective than N. sativa powder in reduction of FPG. To sum up, N. sativa consumption has a significant lowering effect on glycemic status. Further studies with prolonged durations and powerful design are needed to specify the exact mechanism, optimal dosage, and duration of N. sativa supplementation to obtain a beneficial effect on glycemic status.