Figures (2)  Tables (2)
    • Figure 1. 

      Chemical structures of the primary polyphenols in tea.

    • Figure 2. 

      The mechanisms of tea bioactive components (tea polyphenols, polysaccharides, and alkaloids) help prevent and treat DM and its complications (image source from Freepik.com).

    • Categories of hypoglycemic medicinesCommon clinical drugsHypoglycemic mechanismsAdverse effects
      InsulinInsulinEnhance glucose uptake and utilization by systemic tissues and cells while inhibiting glycogenolysis and glycogen isogenesis.Hypersensitivity, lipodystrophy, and lipohypertrophy
      ThiazolidinedionesRosiglitazone; PioglitazoneIncrease insulin sensitivity in liver, muscle, and adipose tissue.Abnormal liver function and weight gain
      BiguanidesPioglitazone; Buformin; MetforminInhibit hepatic glucose output, improve the insulin sensitivity of peripheral tissues, and increase glucose uptake and utilization.Loss of appetite, nausea, abdominal discomfort, and diarrhea
      SulfonylureasGlimepiride; Gliquidone; Gliclazide; GlipizideReduce blood glucose levels by stimulating β-cells insulin secretion.Hypoglycemic reaction, loss of appetite, nausea and vomiting, diarrhea, and increased risk of cardiovascular disease
      Dipeptidyl peptidase-4
      (DPP-4) inhibitors
      Linagliptin; Saxagliptin; VigliptinReduce glucagon and hypoglycemia.Nasopharyngitis, headache, and upper respiratory tract infection
      Glucagon-like peptide 1
      (GLP-1) receptor agonist
      Lixisenatide; Albiglutide; Dulaglutide; SemaglutideReduce blood glucose levels by increasing insulin secretion and inhibiting postprandial glucagon secretion.Nausea, vomiting, diarrhea, injection-site inflammation, and pancreatitis
      α-Glucosidase inhibitorsAcrobose; Miglitol; VogliboseHinder the decomposition and absorption
      of dietary carbohydrates by inhibiting pancreatic α-amylase and intestinal α-glucosidase.
      Gastric flatulence and diarrhea
      Sodium-glucose-cotransporter type-2 (SGLT-2) inhibitorsCanagliflozin; Ertugliflozin; Dapagliflozin; EmpagliflozinInhibit glucose reabsorption in the kidney and eliminate glucose from the urine.Urinary tract infection

      Table 1. 

      Summary of the categories of hypoglycemic medicines, common clinical drugs, hypoglycemic mechanisms, and adverse effects.

    • Tea/bioactive componentsAnimal modelsDoses (day)Duration (weeks)Effects and mechanismsRef.
      Yellow tea extractC57BL/6J mice60 or 120 mg/kg10Improves impaired glucose tolerance, pyruvate tolerance, and insulin resistance.[45]
      Black tea extractWistar rats25, 50, or 100 mg/kg30 dDecreases the level of glucose, glycated hemoglobin and increases the levels of insulin.[47]
      White tea extractWistar rats/8Improves glucose tolerance and insulin sensitivity.[48]
      Pu-erh tea extractWistar rats120, 160, 600, or
      800 mg/kg
      6Increases the abundance of the beneficial bacteria.[49]
      Fu brick tea extractC57BL/6J mice100, 200, or
      400 mg/kg
      8Ameliorates the T2DM-induced gut dysbiosis by decreasing the Firmicutes/Bacteroidota ratio at the phylum level.[50]
      Liubao tea extractC57BL/6J mice834 or 1,667 mg/kg10Increases the diversity of intestinal flora.[51]
      Tea polyphenolsWistar rats200 mg/kg6Improves insulin sensitivity and decreases the inflammatory factors.[55]
      KaempferolSprague–Dawley rats50 or 150 mg/kg10Enhances insulin sensitivity.[56]
      TheaflavinsSpontaneously diabetic torii rats25 mg/kg20Improves impaired glucose tolerance.[57]
      Tea polysaccharidesICR mice150, 200, or 300 mg/kg4Improves insulin resistance.[60]
      EGCG; Epiafzelechin-3-gallate; ECG///Exhibits inhibitory effects against α-glucosidase.[64]
      Oolong tea polyphenols; EGCG; EGCG3″Me///Exhibits inhibitory effects against α-amylase.[67]
      Quercetin-3-O-(6″-O-galloyl)-β-galactopyranoside; Quercetin-3-O-(3″-O-galloyl)-β-glucopyranoside///Exhibits inhibitory effects against α-glucosidase.[68]
      Tea polysaccharidesICR mice1 or 5 mg/kg/Exhibits inhibitory effects against α-glucosidase.[69]
      Tea polysaccharidesICR mice50 mg/kg/Exhibits inhibitory effects against α-glucosidase.[70]
      Tea polysaccharides///Exhibits inhibitory effects against α-amylase and α-glucosidase.[71]
      Tea polysaccharides///Exhibits inhibitory effects against α-glucosidase.[72]
      Tea polysaccharidesC57BL/6 mice200, 400, or
      800 mg/kg
      8Increases the phylogenetic diversity of HFD-induced microbiota.[76]
      EGCGDb/db mice10, 50, or 100 mg/kg8Increases the abundance of beneficial bacteria.[78]
      Tea polysaccharidesWistar rats100, 200, or
      400 mg/kg
      /Modulates gut microbiota diversity and increases the abundance of beneficial genera.[79]
      QuercetinWistar rats50 mg/kg3Exhibits anti-inflammatory activity.[82]
      CaffeineKK-Ay mice250 mg/L5Reduces inflammatory cytokine expression (TNFα, IL-6, and MCP-1).[83]
      EGCGDb/db mice2.5, 5.0, or 10.0 g/kg7Decreases the PEPCK mRNA expression in the adipose and liver tissues.[87]
      Tea polyphenolsWistar rats200 mg/kg6Upregulates the insulin signaling protein levels.[55]
      Tea polysaccharidesKunming mice200, 400, or
      800 mg/kg
      4Upregulates the expressions of the critical proteins in the PI3K/Akt signal pathway including GLUT4, p-Akt, and PI3K.[90]
      Tea polyphenols; Tea polysaccharides; CaffeineSprague–Dawley rats400 or 800 mg/kg6Reduces rat serum leptin levels, inhibits the absorption of fatty acids, and reduces the expression levels of the IL-6 and
      TNF-α genes.
      [91]
      ECSprague–Dawley rats50 or 100 mg/kg2Improves advanced glycation end products-induced retinal vascular injury.[94]

      Table 2. 

      The effects and mechanisms of tea and its bioactive components on DM based on in vitro and in vivo studies