The effect of Nigella sativa on the measures of liver and kidney parameters: A systematic review and meta-analysis of randomized-controlled trials

The aim of this systematic review and dose-response meta-analysis was to determine the effect of Nigella sativa (N.S) supplementation on liver and kidney parameters. We searched PubMed, Scopus, ISI Web of Science, Cochrane central register for controlled trials and Google Scholar from database inception to April 2019 for relevant controlled trials. Mean differences and standard deviations for each outcome were pooled using a random-effects model and a dose-response analysis was performed using a fractional polynomial model. Quality of evidence was evaluated using Cochrane Collaboration Risk of Bias tool and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology. Nineteen trials (n = 1295 participants) were included in the meta-analysis. We observed that N.S supplements had significant reducing effects on alkaline-phosphatase (ALP) [9 trials, n = 710 participants, weighted mean difference (WMD) = -10.825; 95 %CI: -19.658, -1.992 U/L; P = 0.016; I-2 = 75.7 %; P-heterogeneity = 0.000) and blood urea nitrogen (BUN) (12 trials, n = 821 participants, WMD = -1.016; 95 % CI: -1.760, -0.273 U/L; P = 0.007; I-2 = 87.7 %; P-heterogeneity = 0.000) concentrations. Subgroup analysis showed that, an intervention of more than 12 weeks was found to have a reducing effect on aspartate- aminotransferase (AST) measures (2 trials, n = 201 participants, WMD = -11.317; 95 % CI: -15.007, -7.626; P = 0.000; I-2 = 0.0 %; P-heterogeneity = 0.977). Creatinine levels increased significantly in studies that considered adjusted analysis based on covariates (3 trials, n = 152 participants, WMD = 0.070; 95 % CI: 0.027, 0.112 U/L; P = 0.001; I-2 = 0.0 %; P-heterogeneity = 0.788). A daily dose of 1100-1500 mg of N.S supplements was observed to have a substantial reducing effect on ALP levels (5 trials, n = 340 participants, WMD = -11.323; 95 % CI: -21.418, -1.229 U/L; P = 0.028; I-2 = 0.00 %; P-heterogeneity = 0.686), while a dosage of more than 2000 mg per day led to a significant increase in BUN concentrations (2 trials, n = 101 participants, WMD = -1.016; 95 % CI: -1.760, -0.273 U/L; P = 0.007; I-2 = 87.7 %; P-heterogeneity = 0.000). Our data suggested that N.S supplementation had significant impacts on liver and kidney parameters leading to a decrease in ALP and BUN levels. Longer duration of intervention and normal daily dosages of N.S supplements led to significant reductions in ALP and AST concentrations, respectively, while higher daily dosages increased BUN levels. Hence, in spite of favorable impacts of N.S supplements on liver and kidney parameters, due to the herbal nature of N.S, more studies with high-quality, large-scale, long-term intervention and precise baseline characteristics are needed to assess the exact effective dose, duration and efficacy of N.S supplementation on kidney and liver parameters.