The effect of sumac (Rhus coriaria L.) supplementation on glycemic indices: A systematic review and meta-analysis of controlled clinical trials.

BACKGROUND & AIMS: Rhus coriaria L. (Sumac) is a popular spice/herb with several biological functions owing to its antioxidant and insulin-like activities. Many clinical trials have indicated the potent anti-diabetic property of sumac but the results on few glycemic indices were inconclusive. Hence, this systematic review and meta-analysis were aimed to investigate sumac supplementation effect on glycemic indices. METHODS: Systematically searched was performed by two independent reviewers using online databases including: PubMed, Scopus, web of science, EMBASE from inception until November 2020. Data were pooled using a random-effects model and weighted mean difference (WMD) with 95 % confidence intervals (CI). RESULTS: A total of 6 potentially relevant clinical trials met the inclusion criteria with total of 278 participants. Random-effects meta-analysis suggested no significant effects on the levels of fasting blood glucose -7.08 mg/dl, 95 {\%} CI: -14.85 to 0.70,P = 0.07, I(2) = 59.8 {\%}, glycosylated hemoglobin (HbA1c) -0.48 {\%}, 95 {\%} CI: -1.01 to -0.04, P = 0.07, I(2) = 0.0 {\%}, homeostatic model assessment for insulin resistance (HOMA-IR) -0.97, 95 {\%} CI: -1.96 to 0.02, P = 0.05, I(2) = 83.8 {\%}, and insulin -2.94 Hedges' g, 95 {\%} CI: -6.67 to 0.80, P = 0.12, I(2) = 83.1 {\%} following supplementation with sumac powder. CONCLUSION: This meta-analysis showed no significant effects on any glycemic indices following supplementation with sumac powder.