Nigella sativa improves glucose homeostasis and serum lipids in type 2 diabetes: A systematic review and meta-analysis

Background & objective(s): Global prevalence of type 2 diabetes (T2D) is very high and is currently growing alarmingly. With respect to recent researchers' attention to the potential role of herbal medicine in disease prevention and management, the present meta-analysis review investigates the effectiveness of Nigella sativa (N. sativa), a popular herb, in T2D. Methods: Literature search was conducted covering PubMed/Medline, Scopus, and Cochrane Registry of Clinical Trials up to February 2017 to obtain the relevant published intervention studies. Study selection, quality rating and data extraction of studies were investigated by two independent reviewers. Heterogeneity was assessed using I-squared (I-2) statistics test. Subgroup analysis was done to assess type of N. sativa supplement as source of heterogeneity. Effect sizes of eligible studies were pooled using STATA software version 12 (STATA corp, College Station, Tx, USA). Results: Seven trials were included in the meta-analysis of glycemic and serum lipid profile end points. Supplementation with N. saliva significantly improved fasting blood sugar (FBS) [-17.84 mg/dl, 95% CI: -21.19 to -14.49, p < 0.001], HbA1c [-0.71%, 95% CI: -1.04 to -0.39, p < 0.001], total-cholesterol (TC) [WMD: -22.99 mg/dl, 95% CI: -32.16 to -13.83, p < 0.001] and LDL-cholesterol (LDL-c) [-22.38 mg/dl, 95% CI: -33.60 to -11.15, p < 0.001]. The overall effects for triglyceride (TG) [-6.80 mg/dl, 95% CI: -33.59 to 19.99, p = 0.61] and HDL-cholesterol (HDL-c) [0.37 mg/dl, 95% CI: -1.59 to 2.33, p = 0.71] were insignificant. Subgroup analysis revealed significant reduction on TG with N. saliva seed oil [-14.8 mg/dl, 95% CI: -23.1 to -6.5, p < 0.001], while TG was increased with seed powder [29.4 mg/dl, 95% CI: 16.9-42.0, p < 0.001]. All measures, but HbA1c, showed no evidence of publication bias. Conclusion: Although, the meta-analysis conducted included a few number of studies, but has shown promising results on the effectiveness of N. saliva on glucose homeostasis and serum lipids. Current findings suggest N. saliva supplementation a suitable choice in managing the complications of T2D, although future researches are necessary.