INS and type 2 diabetes mellitus: Therefore, the present umbrella meta-analysis aimed to examine the effects of cinnamon supplementation on serum levels of fasting plasma glucose (FPG), homeostatic model assessment for insulin resistance (HOMA-IR), insulin, and hemoglobin A1c (HbA1c) by performing a meta-analysis on the previously published meta-analyses of randomized clinical trials (RCTs) in patients with T2D or PCOS.