Curcumin or combined curcuminoids are effective in lowering the fasting blood glucose concentrations of individuals with dysglycemia: Systematic review and meta-analysis of randomized controlled trials

[Display omitted] Curcuminoids have received considerable attention as therapeutical adjuvants in the treatment of dysglycemia. The purpose of this meta-analysis was to evaluate whether the supplementation of turmeric extract, curcuminoids and/or isolated curcumin is more effective than placebo in decreasing fasting blood glucose (FBG) in adults. MEDLINE, CENTRAL, ScienceDirect and gray literature databases were searched. Randomized controlled trials with the following criteria were included: (1) studied individuals older than 18 years, supplemented with curcumin, curcuminoids and/or turmeric extract (2) had a follow-up ≥4 weeks (3) used a placebo group. Titles and abstracts were screened and potentially eligible articles were retrieved. The primary outcome was FBG. The secondary outcomes were HbA1c and HOMA-IR. Eleven studies were included. In the overall analysis, turmeric, curcuminoids and curcumin supplementation led to a decrease in FBG (−8.88, 95% CI: [−5.04 to −2.72] mg/dL, p = 0.005). Supplementation of curcuminoids and/or curcumin decreased the concentrations of HbA1c (−0.54, 95% CI: [−1.09 to −0.002] %, p = 0.049) but were not able to decrease HOMA-IR (−1.26, 95% CI: [−3.71 to −1.19], p = 0.31). Sensitivity analyses revealed that baseline FBG was an important covariate. Heterogeneity was high in the overall analyses and there was evidence of publication bias. Supplementation of isolated curcumin or combined curcuminoids were both effective in lowering the FBG concentrations of individuals with some degree of dysglycemia, but not in non-diabetic individuals. Isolated curcumin lead to significant decreases of the HbA1c compared to placebo.