Introduction
Previously, we demonstrated that a 10-day mild cold acclimation (14-15°C, 6h/day) robustly improved insulin sensitivity in patients with type 2 diabetes (T2D), partly via an enhanced glucose transporter 4 (GLUT4) translocation in skeletal muscle. Although non-shivering thermogenesis is involved in mild cold acclimation, a follow-up study indicated that some level of (mild) muscle activity/shivering appears crucial in provoking the beneficial metabolic effects of cold acclimation. Therefore, we here investigated the effects of repeated bouts of cold-induced shivering on glucose homeostasis.

Methods
In a single-arm intervention study, 15 overweight/obese men and (postmenopausal) women (n=11 and 4, respectively, 40-75 years, BMI: 27-35 kg/m²) were underwent 10 consecutive days of intermittent cold-induced shivering thermogenesis (10˚C with 1h of shivering/day) via a water-perfused suit. Shivering thermogenesis was confirmed, by surface electromyography and visual observation. Before and after the intervention, a 2-hour oral glucose tolerance test (OGTT) was performed in the overnight fasted state, under thermoneutral conditions. Prior to the OGTTs, heart rate and blood pressure were measured and muscle biopsies were taken.

Results
Repeated exposure to cold-induced shivering significantly reduced fasting plasma glucose concentrations (5.84±0.38 vs 5.67±0.32 mmol/L, p=0.013) and improved glucose tolerance during the OGTT by 6% (total area under the curve: p=0.041). Plasma insulin concentrations at baseline and during the OGTT were unaffected. Interestingly, fasting plasma triglyceride and free-fatty acid concentrations robustly decreased by 32% and 11% (p=0.001 and p=0.036, respectively). Additionally, cold acclimation markedly reduced systolic and diastolic blood pressure by 7.4% (p<0.001) and 8.1% (p<0.001), respectively, and tended to decrease resting heart rate (p=0.062) (measured at thermoneutrality). No effects were observed in myocellular membrane and total GLUT4 expression.

Conclusion
Repeated exposure to cold, leading to cold-induced shivering thermogenesis, improved glucose homeostasis and other clinically relevant metabolic health parameters in overweight/obese individuals, indicating its preventive and therapeutic potential for T2D.