The antidiabetic effect of thymoquinone: A systematic review and meta-analysis of animal studies

Thymoquinone (2-isopropyl-5-methylbenzo-1, 4-quinone) (TQ) is a quinone derivative with a yellow crystalline appearance, abundantly found in black cumin, Nigella sativa L. TQ has diverse pharmacological properties. The aim of this systematic review on the antidiabetic effects of TQ is to evaluate the currently available evidence and conduct meta-analysis. A literature search of articles published until 25 January 2019 was done on PubMed, EMBASE, Web of Sciences and Scopus databases, using relevant keywords. The meta-analysis included 18 studies that examined the serum glucose (SG) level or serum insulin level or body weight (BW). In the meta-analysis it was found that with an overall pooled standardized mean difference (SMD) of - 9.176 mg/dl (95%CI: - 10.759, - 7.593; p = 0.000); TQ reduced the SG level (- 9.176 mg/dl) significantly in the STZ-induced diabetes model. Moreover, a meta-analysis of the effect of TQ on BW demonstrated that TQ has a statistically significant effect on the BW of diabetic animals with an overall pooled SMD of 4.509 (95%CI: 3.234, 5.784; p = 0.000). In addition, the overall pooled estimate of the level of serum insulin was significant with SMD of 1.681 (95%CI: 0.858, 2.503; p = 0.000). Therefore, the meta-analysis showed that TQ has a significant antidiabetic effect through its action on the SG, serum insulin level, and BW of the animals.