Hypoglycemic Effect of Black Tea and Its Mechanism: Regulation of Glycometabolism and Intestinal Flora

This study aimed to investigate the hypoglycemic effects of different concentrations of black tea (BT) extracts and their underlying mechanisms in type 2 diabetic (T2DM) mice. Results indicated that BT extracts significantly mitigated weight loss, improved glucose and insulin tolerance, and modulated cytokine levels related to glucose and lipid metabolism in T2DM mice. Moreover, BT extracts ameliorated liver and pancreas damage resulting from high-sugar/high-fat diets and insulin resistance. Among the tested concentrations, low-concentration BT (BT-L) extract exhibited the most potent hypoglycemic ability. Furthermore, BT-L restored pancreatic function in hyperglycemic mice via activating the glucagon-like peptide-1 receptor-protein kinase A-pancreatic and duodenal homeobox-1-glucokinase cascade pathway. In terms of intestinal homeostasis, all BT-treated groups adjusted the gut microbiota structure by regulating the distribution and diversity of gut microbiota in T2DM mice. Among them, BT-L intervention specifically and significantly increased the levels of probiotic Bifidobacterium in the intestine of T2DM mice. Furthermore, BT-L intervention effectively promoted the synthesis of streptomycin by gut microbiota, thereby exerting anti-inflammatory effect. Comprehensively, the hypoglycemic effect of BT cannot show an absolute concentration-dependent relationship. Our findings highlight the potential of BT as an effective blood glucose regulator and provide valuable insights for BT-based functional food development.