Effects of swimming training in hot and cold temperatures combined with cinnamon supplementation on HbA1C levels, TBC1D1, and TBC1D4 in diabetic rats

The study addresses how exercise temperature and cinnamon supplementation influence glucose regulation pathways in diabetes. Diabetes prevalence is rising, and non-pharmacological interventions such as exercise and nutraceuticals are sought to improve insulin sensitivity and glycemic control. TBC1D1 and TBC1D4 are key regulators downstream of insulin/Akt and AMPK that control GLUT4 trafficking. The authors hypothesized that combining cold-water exercise, which may enhance insulin sensitivity, with cinnamon, which can improve insulin receptor signaling, would beneficially modulate TBC1D1/TBC1D4 and reduce HbA1c in diabetic rats.

Prior work shows insulin and exercise increase GLUT4 translocation via signaling that includes TBC1D1 and TBC1D4. These Rab-GAP proteins are regulated by insulin, AMPK activation, and muscle contraction, and their phosphorylation status relates to GLUT4 vesicle trafficking. Studies have shown mixed adaptations of TBC1D1/D4 to training (increased phosphorylation or unchanged), though exercise often enhances insulin-stimulated signaling. Cold exposure has been reported to improve glucose tolerance and insulin sensitivity in rodents and humans with type 2 diabetes. Cinnamon polyphenols can enhance insulin receptor autophosphorylation and inhibit protein tyrosine phosphatase, improving insulin sensitivity, though findings on HbA1c outcomes are mixed across clinical trials. No prior studies directly examined effects of exercise water temperature on TBC1D1/TBC1D4.

Design: Experimental study with seven parallel groups (n=13 each). Animals: 91 male rats (8–10 weeks). Diabetes induction: Streptozotocin 55 mg/kg i.p. in 78 rats; 13 healthy controls. Housing: 12h light/dark, 22–24°C, 55% humidity, ad libitum food/water. Group allocation: (1) Healthy control (HC); (2) Diabetic control (DC); (3) Cold-water swim (S5); (4) Cold-water swim + cinnamon (S5+Ci); (5) Warm-water swim (S35; 35–36 °C); (6) Warm-water swim + cinnamon (S35+Ci); (7) Cinnamon only (Ci). Exercise acclimation: One week of swim familiarization; water temperature reduced from 25°C to 5°C; sessions 2 min, 3×/week. Training protocols: Swimming in a 100×50×50 cm tank at 5°C (S5, S5+Ci) or 35–36°C (S35, S35+Ci). Week 1: 2 min/day, 5 days/week, adding 30 s per session until 4 min; weeks 2–8: 4 min/session, 5 days/week. Cinnamon supplementation: Aqueous extract prepared by boiling 200 g cinnamon powder in 1000 ml water for 10 min and filtering; 20% extract (20 mg/ml). Dose: 200 mg/kg body weight; provided via drinking water (1 ml per ~5 rats in cage; dosing aligned to body weight). Duration: 8 weeks concurrent with training. Sample collection: 48 h post-last session, anesthesia (xylazine/ketamine), blood via portal vein; plasma separated (3000 rpm, 10 min). Assays: HbA1c by Pars Azmoon enzymatic kit (Iran). TBC1D1 by ELISA (Zelbio, Germany; sensitivity 100 pg/ml). TBC1D4 by ELISA (Zelbio, Germany; sensitivity 1000 ng/L). Ethics: Institutional approval; care per NIH Guide. Statistics: One-way ANOVA (SPSS); homogeneity and normality tested; Bonferroni post hoc for pairwise comparisons. Effect sizes categorized as small (0.2), medium (0.5), large (≥0.8). Significance p<0.05.

- TBC1D4: Significant group effect, F(6,84)=5.92, p<0.001, η²=0.297. DC and S35 > HC (p<0.001). S5+Ci < DC, S5, S35, and S35+Ci (p<0.001). Other comparisons NS. - TBC1D1: Significant group effect, F(6,84)=8.51, p<0.001, η²=0.378. DC, S35, and S35+Ci > HC (p<0.001). S5+Ci showed significantly lower levels than DC, S5, S35, and S35+Ci (as described in results and figures). Other comparisons NS. - HbA1c: Significant group effect, F(6,84)=6.25, p<0.001, η²=0.309. DC, Ci, and S35 > HC (p<0.001). S5+Ci lower than DC, Ci, and S35 (p<0.001). S5 < DC (p=0.018). Overall, cold-water swim (S5) and especially cold-water swim with cinnamon (S5+Ci) reduced HbA1c. - Overall: Combining cold-water swim with cinnamon (S5+Ci) most effectively reduced TBC1D1, TBC1D4, HbA1c, and glucose versus other conditions.

The findings support the hypothesis that combining cold-environment exercise with cinnamon supplementation favorably modulates key glucose-transport regulators (TBC1D1/TBC1D4) and glycemic indices in diabetes. Elevated TBC1D1/TBC1D4 in diabetic and warm-water–trained rats versus healthy controls suggests adverse or insufficient adaptation under those conditions. In contrast, the cold-water plus cinnamon intervention lowered TBC1D1/TBC1D4, consistent with enhanced GLUT4 trafficking and insulin action via insulin/Akt and AMPK-related pathways. Reduced HbA1c with cold-water training (with or without cinnamon) aligns with evidence that cold acclimation can improve insulin sensitivity, whereas warmer environments are associated with higher HbA1c. Cinnamon’s insulin-sensitizing actions (e.g., promoting insulin receptor autophosphorylation and inhibiting receptor phosphatase) may have complemented cold-induced metabolic adaptations. Together, these results indicate a synergistic, non-traditional approach to improving insulin sensitivity and glycemic control in a diabetic model.

Eight weeks of cold-water swimming combined with cinnamon supplementation significantly reduced TBC1D1, TBC1D4, and HbA1c in diabetic rats, with cold-water exercise alone also lowering HbA1c. Exercising in a cold environment, particularly with cinnamon, may serve as an effective strategy to improve insulin sensitivity and glucose indices. Further studies are warranted to elucidate underlying mechanisms and to evaluate translation to clinical populations.