Ardiana M, Pikir BS, Santoso A, Hermawan HO, Al-Farabi MJ. Effect of Nigella sativa supplementation on oxidative stress and antioxidant parameters: A meta-analysis of randomized controlled trials. Scientific World Journal. May 6, 2020;2020:2390706. doi: 10.1155/2020/2390706. eCollection 2020.
Oxidative stress is associated with diseases such as coronary heart disease, chronic obstructive pulmonary disease, neurodegenerative diseases, cancer, and chronic kidney disease. Nigella (NS; Nigella sativa, Ranunculaceae) seed has been shown to have bronchodilator, gastroprotective, hepatoprotective, antitumor, antidiabetic, antihypertensive, antioxidant, antifungal, immunomodulatory, anti-inflammatory, analgesic, antiviral, antipyretic, contraceptive, antimicrobial, anticonvulsant, antitussive, anticancer, antihyperlipidemic, and antibacterial properties. NS has been shown to reduce the production of reactive oxygen species (ROS) by acting as a free radical scavenger. Previous studies have shown that NS may increase the production and activity of antioxidant enzymes such as superoxide dismutase (SOD). However, clinical trials show conflicting results with NS supplementation and oxidative stress and antioxidant activity. The purpose of this meta-analysis was to determine the effects of NS supplementation on oxidative stress parameters and antioxidant enzyme production, including MDA, SOD, and total antioxidant capacity (TAC).
Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. A keyword search was performed through PubMed/Medline, SCOPUS, and Google Scholar databases. Reference lists of eligible articles, related reviews, and meta-analyses were also reviewed. Works cited by all selected original research articles and reviews were also searched for additional and/or missing articles not identified in the keyword search. Randomized controlled trials (RCTs) conducted on patients ≥ 18 years old that evaluated the effects of NS on oxidative parameters and/or antioxidant enzymes were included. Additionally, full-text articles written in English that reported study parameters before and after the intervention in both placebo and treatment groups were also included. Nonclinical trials conducted on children, pregnant women, or animals were excluded. Nonplacebo-controlled trials, those lacking sufficient data for the outcomes of interest, and studies examining the effects of NS supplementation with other interventions were also excluded.
A total of 167 articles were identified through the keyword search. No additional articles were discovered. Of those, 157 were duplicates (n = 53) or excluded based on title or abstract (n = 104). Ten full-text articles were assessed for eligibility. Five were either not placebo-controlled (n = 3), combined NS with other interventions (n = 1), or did not evaluate the outcomes of interest (n = 1), and thus, were excluded. The pooled sample size of the five included studies was 293 patients (men and women) with 152 in the NS groups and 141 in the control groups. The age ranged between 18 and 60 years. The articles were published between 2015 and 2018. Four were conducted in Iran, and one in Saudi Arabia. Three RCTs used doses of 500 mg/day; one, 2 g/day; and one, 3 g/day. One study was conducted over six weeks, two over eight weeks, and one over 48 weeks. Three trials were conducted solely on women, and the remaining two on both genders. Patients were diagnosed with type 2 diabetes in one study; two, rheumatoid arthritis; one, obesity; and one, ulcerative colitis. All of the RCTs were parallel-design clinical trials.
One study reported a significant reduction in MDA after NS supplementation compared to the control (P value not given). A different study found a significant increase in TAC in the NS group compared to the control (P value not given). Two studies showed an increase in SOD in the NS group compared to the control; whereas, two studies showed a reduction in SOD. Only one study reported a significant reduction in SOD for the NS group compared to the control (P value not given).
Results of the meta-analysis from four studies showed that NS supplementation did not significantly reduce MDA or increase TAC when compared to the controls. However, meta-analysis showed a significant increase in SOD with NS supplementation compared to the controls (P = 0.01).
The limitation of this meta-analysis included a lack of standardization between the studies with regard to dose, disease type and severity, supplement duration, as well as a lack of regulation for nutraceutical products. The authors recommend that further clinical trials with such standardization parameters are needed. The authors conclude that NS supplementation significantly increased the antioxidant enzymes represented by SOD but had no effect on TAC or MSA.
The authors declare no conflict of interest.