Review of Black Cumin for Metabolic Disorders
Black cumin (Nigella sativa, Ranunculaceae) seed is popular in the Middle East and Southeast Asia for treating diabetes, dyslipidemia, hypertension, and obesity. However, clinical evidence is inconclusive. The purpose of this systematic review was to evaluate the clinical and biochemical effects of black cumin on lipid profiles, glycemic factors, blood pressure, and anthropometric indices (weight, body mass index [BMI], and waist circumference), all of which are parameters of metabolic syndrome.
The following databases were searched from inception through June 2014: PubMed, Google Scholar, Thomson Reuters Web of Science, and Cochrane. The following medical subject headings (MeSH) and title/abstract (tiab) search terms were used: (“Nigella sativa” [MeSH] OR “black seed” [tiab] OR “black cumin” [tiab] OR “Kalonji” [tiab]) AND “Triglycerides” [MeSH] OR “Cholesterol” [MeSH] OR “Lipoproteins, LDL” [MeSH] OR “Lipoproteins, HDL” [MeSH] OR “Blood glucose” [MeSH] OR “Hemoglobin A, Glycosylated” [MeSH] OR “Blood pressure” [MeSH] OR “Body mass index” [MeSH] OR “Waist circumference” [MeSH]). The inclusion criteria were (1) published in English, (2) the effect of black cumin on clinical or biochemical parameters, and (3) clinical trial. The exclusion criteria were (1) animal studies, (2) review studies, (3) the effect of black cumin on unrelated blood or clinical parameters, (4) the effect of black cumin combined with other plants or exercise, and (5) duplicated studies.
A total of 515 articles were located, and 18 studies (with a total of 1531 subjects) met the inclusion/exclusion criteria. The studies were highly heterogeneous: five studies were randomized, double-blind, controlled studies; five studies had no control group, and eight studies were randomized controlled studies. Included patients were aged 18-65 years and had diabetes (n = 5 studies), metabolic syndrome (n = 7 studies), hyperlipidemia (n = 4 studies), hypertension/coronary disease (n = 2 studies), obesity (n = 1 study), or were healthy subjects (n = 4 studies). All treatments were oral and doses ranged from 200 mg/day to 5 g/day of seed extract (n = 2 studies), seed oil (n = 8 studies), or seed powder (n = 13 studies). Treatment duration ranged from two weeks to six months.
Table 1 summarizes the study findings. The authors note significant findings; however, they do not report whether the changes are compared with baseline or control. In Table 1, the column titled “overall effect” indicates which parameters had more evidence in favor of a significant improvement.
Table 1: Summary of Number of Studies with Significant Improvements in Measured Parameters
|Number of Studies|
|Parameters||Significant improvement||No significant effect||Overall effect (Yes/No)|
|Low-density lipoprotein (LDL) cholesterol||11||3||Yes|
|High-density lipoprotein (HDL) cholesterol||6||10||No|
|Fasting blood sugar||13||3||Yes|
Based on the number of studies demonstrating a significant improvement, the evidence weighs more in favor of black cumin improving total cholesterol, LDL, fasting blood sugar, and glycosylated hemoglobin. Evidence does not support an effect of black cumin on blood pressure or anthropometric indices. A total of 10 studies evaluated safety. Two studies that treated subjects with 5 mL/day black cumin seed oil reported mild nausea that resolved after one week of treatment. Eight studies measured liver and kidney function and reported no adverse effects.
The authors conclude that black cumin should be “a complementary treatment protocol for many diseases, especially metabolic disorders.” However, even though the evidence leans more favorably in the direction of a benefit for some parameters, the heterogeneity of the studies must be taken into consideration. It would have been advantageous if the researchers conducted a meta-analysis to provide more scientific rigor to their analysis and conclusions. Recommendations for the effective dose or preparation cannot be gleaned from this analysis. More research is needed if black cumin is to be recommended as a treatment for patients with symptoms of metabolic syndrome.
Mohtashami A, Entezari MH. Effects of Nigella sativa supplementation on blood parameters and anthropometric indices in adults: A systematic review of clinical trials. J Res Med Sci. 2016;21:3. doi: 10.4103/1735-1995.175154.