Cold exposure could help combat type 2 diabetes, particularly if it provokes shivering

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The European Association for the Study of Diabetes (EASD), Annual Meeting in Stockholm, Sweden (19-23 September) will present new research that shows that shivering in cold temperatures improves glucose tolerance, reduces fasting blood sugar levels and blood fat levels, and significantly lowers blood pressure in obese and overweight adults.

Adam Sellers, Stenvan Beek and colleagues from Maastricht University, The Netherlands, have done a preliminary study that highlights the potential for repeated cold exposure to activate shivering as an alternative strategy for treating and preventing type 2 diabetes (T2D).

Previous research has shown that glucose is more efficiently cleared from the blood when people are cold. Brown fat was believed to play an important role in lowering blood glucose levels and improving insulin sensitivity. This could help to reduce insulin resistance, and other diseases like diabetes, such as type 2 diabetes.

Sellers explains that brown fat is a metabolic heating mechanism in our bodies that burns calories. This generates heat and prevents calories being stored as normal white fat. Brown fat activates when it is cold and when we eat. However, its activity is lower in older adults and people with diabetes and obesity.

A previous study demonstrated that 10 days of mild cold acclimation (14 to 15°C, 6 hours per day) markedly improved insulin sensitivity in patients with T2D. The significant improvement in insulin sensitivities was not explained by the minor change in brown fatty acids after cold acclimation. However, cold acclimation resulted in glucose transporter 4 (GLUT4) translocation within skeletal muscle. This is when GLUT4 moves into a more favorable position, which facilitates glucose clearance.

But although non-shivering thermogenesis—which generates heat from stored energy without muscle contraction—is involved in mild cold acclimation, a follow-up study indicated that some level of (mild) muscle activity/shivering may be crucial in activating the beneficial metabolic effects of cold.

“When we feel cold, we can activate our Brown Fat because it burns heat and releases energy to protect us. Furthermore, muscle can contract or shiver mechanically, generating heat. Sellers explains that because there is more muscle in a human than brown fat, shivering can burn more calories as well as produce more heat.

To find out more, researchers exposed volunteers—11 men and 4 postmenopausal women with overweight or obesity (aged 40-75 years, BMI 27-35 kg/m²)—to 10 consecutive days of cold to activate shivering, using a water-perfused suit to control and lower body temperature. Participants were exposed to cold, from 32°C to 10°C, until they shivered for one hour per day.

Special devices were placed on the skin to monitor shivering and detect muscle electrical activity. The one-hour period of shivering began when resting energy expenditure rose by 50%.

Before and after the intervention, a 2-hour oral glucose tolerance test (OGTT) was performed under thermoneutral conditions—the environmental temperature where the body does not need to produce heat to maintain its core temperature. Researchers also measured heart beat and blood pressure, and took muscle biopsies in order to assess potential changes in muscle related to glucose metabolism.

The results showed that repeated cold-induced shivering significantly decreased average fasting plasma glucose concentrations by 5.84 to 5.67 mg/L and improved glucose tolerance by 6%.

The shivering intervention did not affect plasma insulin concentrations. This suggests that the increased fasting glucose and glucose tolerance following repeated shivering are not due to an increase in insulin levels.

Fasting plasma triglyceride levels and free-fatty acids concentrations were significantly reduced by 32%, 11%, and respectively. These fat fuels are the most important in the body and are believed to increase the risk of developing cardiovascular disease and insulin resistance.

Repetitive cold exposure also reduced systolic (and diastolic) blood pressure by approximately 10 mmHg each. It also had a tendency to lower resting heart rate when measured in thermoneutral conditions.

Surprisingly, the translocation of muscle GLUT4 was not affected by the shivering. This suggests that other changes may have occurred in skeletal muscles and/or other organs, which could explain the increased glucose tolerance.

The authors acknowledge that there are limitations, including the inability for strong causal conclusions to be drawn about the direct effect cold exposure has on metabolic health. The authors also acknowledge that, despite the fact that measures have been taken to control diet, physical activity, other lifestyle factors or genetic factors could impact the findings.

“But, this is an important step in investigating the health effects of shivering. Sellers states that our findings are promising, and may have important implications for health. “Shivering improved many cardiometabolic outcomes which are associated to diseases such as type 2 diabetes,” Sellers said. “In future studies, our goal is to evaluate the effects of shivering on adults with type 2 diabetes.

Is it cold enough to freeze? Exercise may protect against muscle fatigue

Cold exposure may help to combat type 2 diabetes, especially if it causes shivering (2022, Sept 21).
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