Shivering during repeated cold exposure improves glucose tolerance, decreases fasting blood sugar and blood fat levels, and significantly lowers blood pressure in overweight and obese adults, according to new research.
The early study, conducted by Adam Sellers, Sten van Beek, and colleagues at Maastricht University in the Netherlands, indicates the potential for repeated cold exposure that induces shivering as an alternate strategy for treating and preventing type 2 diabetes (T2D).
Previous research has demonstrated that when humans are cold, glucose is removed from the bloodstream more quickly. According to previous research, brown fat significantly lowers blood sugar levels and improves insulin sensitivity in people, which lowers insulin resistance and lowers the chance of developing disorders like diabetes.
According to Sellers, “brown fat is a metabolic heating system inside our bodies, burning calories.”
This produces heat and stops calories from accumulating as typical white fat. When we are chilly and when we eat, brown fat is activated, but older adults and people with obesity and diabetes have reduced brown fat activity.
An earlier study showed that modest cold acclimation for 10 days (14 to 15°C, 6 hours per day) significantly increased insulin sensitivity in T2D patients. However, the change in brown fat after cold acclimation was small and could not account for the significant improvement in insulin sensitivity. But during cold acclimation, skeletal muscle glucose transporter 4 (GLUT4) translocation was improved (during which GLUT4 moves to a more advantageous position, facilitating glucose removal from the circulation and into the muscle).
Despite the fact that non-shivering thermogenesis, which creates heat from stored energy without muscular contraction, is involved in mild cold acclimation, a follow-up study revealed that (mild) muscle activity/shivering may be essential for triggering the favourable metabolic effects of cold.
“When we are cold, we can activate our brown fat because it burns energy and releases heat to protect us,” adds Sellers.
“In addition, muscle can contract mechanically, or shivers, thereby generating heat. As there is considerably more muscle than brown fat in a human, shivering can burn more calories and produce more heat.”
Researchers employed a water-perfused suit to regulate and reduce body temperature while subjecting volunteers—11 men and 4 postmenopausal women with overweight or obesity (aged 40–75 years, BMI 27–35 kg/m2)—to 10 days of cold to induce shivering. For one hour each day, participants were exposed to temperatures between 32°C and 10°C until they began to shiver.
Special devices that could see and sense the electrical activity of muscles were put on the skin and used to track shivering. The one-hour period of shivering began when resting energy expenditure increased by fifty percent.
A 2-hour oral glucose tolerance test (OGTT) was performed before and after the intervention under thermoneutral conditions—the temperature at which the body does not need to create heat to maintain its core temperature. In addition to measuring heart rate and blood pressure, researchers obtained muscle biopsies to identify potential alterations in muscle associated with glucose metabolism, including GLUT4 translocation.
The results showed that frequent cold-induced shivering considerably increased glucose tolerance by 6 percent and decreased average fasting plasma glucose concentrations from 5.84 to 5.67 mmol/L.
After the shivering intervention, plasma insulin concentrations before and during the OGTT remained unaffected. This shows that the elevated insulin levels in the blood were not the source of the better fasting glucose and glucose tolerance following repeated shivering.
It’s interesting to note that the quantities of free fatty acids and triglycerides in fasting plasma were significantly lower, by 32 percent and 11 percent, respectively. These are the primary fat fuels, and research suggests they increase the risk of cardiovascular disease and lead to insulin resistance.
Additionally, when evaluated under thermoneutral settings, repeated cold exposure significantly lowered systolic and diastolic blood pressure by around 10 mmHg and 7 mmHg, respectively, and tended to lower resting heart rate.
Surprisingly, the shivering intervention had no effect on muscle GLUT4 translocation. This shows that other changes occurred in skeletal muscle and/or other organs to account for enhanced glucose tolerance.
The authors acknowledge a number of limitations, including the inability to make conclusive causal conclusions regarding the direct effect of cold exposure on metabolic health. They also point out that, despite efforts to regulate food and exercise, other lifestyle factors or genetic factors that were not examined in the current study could have an impact on the results.
“Nevertheless, this is an important first step investigating the effect of shivering on health. Our findings are promising and may have important health implications, given that shivering improved many cardiometabolic health outcomes which are associated with diseases like type 2 diabetes,” adds Sellers. “In future studies, we plan to assess the effect of shivering in adults with type 2 diabetes.”
The study will be presented at this year’s European Association for the Study of Diabetes (EASD) Annual Meeting in Stockholm, Sweden (19-23 September).
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