Effect of Nigella sativa L. supplementation on inflammatory and oxidative stress indicators: A systematic review and meta-analysis of controlled clinical trials

Abstract

Aims: The objective of the present study was to perform a systematic review and meta-analysis on randomized controlled trials (RCTs) assessing the effects of Nigella sativa L. supplementation on the circulating inflammatory and oxidative stress markers, including C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), total antioxidant capacity (TAC) and malondialdehyde (MDA). Methods: Systematic search was performed up to March 2020 using PubMed, Scopus, and ISI web of science databases. Two reviewers independently assessed study eligibility, extracted data, and evaluated methodological quality of included primary studies. Statistical heterogeneity was assessed using I-square (I-2) statistic. Data were pooled by using the random-effect model and standardized mean difference (SMD) was considered as the summary effect size. Results: Twelve trials were identified to be suitable for our meta-analysis. The pooled results using random effects model indicated that Nigella sativa supplementation significantly reduced CRP (SMD: -0.35; 95 CI: -0.59, -0.12, P < 0.001, I-2 = 10.5) and MDA concentrations (SMD: -0.56; 95 CI:-0.98, -0.15, P < 0.001, I-2 = 64.7). Moreover, Nigella sativa supplementation increased TAC (SMD: 0.48; 95 CI: 0.09, 0.87, P = 0.01, I-2 = 65.6) levels; however, it did not affect TNF-alpha (SMD: -0.35; 95 CI: -0.70, 0.01, P = 0.05, I-2 = 58.2). Conclusion: Nigella sativa supplementation is associated with improved inflammation and oxidative status. Additional prospective studies are recommended using higher supplementation doses and longer intervention period.