New research, presented at this year’s European Association for the Study of Diabetes (EASD) annual meeting in Stockholm, Sweden, finds that shivering during repeated cold exposure improves glucose tolerance, decreases fasting blood sugar and fat and markedly reduces blood pressure in overweight and obese adults .
The preliminary study, conducted by Adam Sellers, Sten van Beek and colleagues at Maastricht University in the Netherlands, highlights the potential of repeated shiver-triggering cold exposure as an alternative strategy to treat and prevent type 2 diabetes ( T2D).
Previous research has shown that when humans are cold, glucose is removed from the blood faster. Brown fat was thought to play an important role in lowering blood glucose and improving insulin sensitivity in humans, helping to reduce insulin resistance and the risk of diseases, including diabetes.
“ Brown fat is a metabolic heating system within our body, which burns calories,” explains Sellers. “This generates heat and prevents calories from being stored as normal white fat. “Brown fat is activated during cold weather and when we eat, but its activity is lower in older adults and in people with obesity and diabetes.”
A previous study demonstrated that 10 days of mild cold acclimatization (14 to 15°C, 6 hours per day) markedly improved insulin sensitivity in patients with T2D. But the change in brown fat after cold acclimatization was smaller and could not explain the large improvement in insulin sensitivity . However, after cold acclimatization, translocation of glucose transporter 4 (GLUT4) in skeletal muscle was enhanced (during which GLUT4 moves to a more favorable position that facilitates the removal of glucose from the blood and into the body). muscle).
But although non-shivering thermogenesis, which generates heat from stored energy without muscle contraction, is involved in mild cold acclimatization, a follow-up study indicated that some level of mild muscle activity (shivering) may be crucial for activating the beneficial metabolic effects of cold.
“When we are cold, we can activate our brown fat because it burns energy and releases heat to protect us. Additionally, the muscle can mechanically contract or twitch, thus generating heat. Because there is considerably more muscle than brown fat in a human being, shivering can burn more calories and produce more heat,” explains Sellers.
To learn more, the researchers exposed volunteers (11 men and 4 overweight or obese postmenopausal women (age 40 to 75, BMI 27 to 35 kg/m²) to 10 consecutive days of cold to activate shivering, using a water perfusion. Participants were exposed to cold, from 32°C to 10°C, until they shivered for one hour a day.
Shivers were monitored by special devices placed on the skin that detect electrical activity of the muscles, as well as visual observation. Shivering time began when resting energy expenditure increased by 50% [3].
Before and after the intervention, a 2-hour oral glucose tolerance test (OGTT) was performed under thermoneutral conditions, the ambient temperature at which the body does not need to produce heat to maintain its core temperature. The researchers also measured heart rate and blood pressure and took muscle biopsies to determine possible changes in the muscle related to glucose metabolism, such as GLUT4 translocation.
The findings showed that repeated cold-induced shivering significantly reduced average fasting plasma glucose concentrations from 5.84 to 5.67 mmol/l and improved glucose tolerance by 6%.
Plasma insulin concentrations before and during OGTT were not affected after the shivering intervention. This suggests that the improvement in fasting glucose and glucose tolerance after repeated shivering was not due to increased blood insulin.
Interestingly, fasting plasma concentrations of triglycerides and free fatty acids were markedly reduced by 32% and 11%, respectively. These are the body’s main fatty fuels and are believed to increase the risk of cardiovascular disease and contribute to insulin resistance.
Furthermore, repeated cold exposure also markedly reduced systolic and diastolic blood pressure by about 10 mmHg and 7 mmHg, respectively, and tended to reduce resting heart rate when measured under thermoneutral conditions.
Surprisingly, muscle GLUT4 translocation did not change after the shivering intervention. This suggests that other changes occurred in skeletal muscle and/or potentially other organs that explain the improved glucose tolerance.
The authors acknowledge several limitations, including the inability to draw strong causal conclusions about the direct effect of cold exposure on metabolic health. They also note that, despite measures taken to control diet and physical activity, other lifestyle factors or genetic factors not measured in the current study could affect the findings.
“However, this is an important first step in investigating the effect of chills on health. “Our findings are promising and may have important health implications, given that shivering improved many cardiometabolic health outcomes that are associated with diseases such as type 2 diabetes,” says Sellers. “In future studies, we plan to evaluate the effect of shivering in adults with type 2 diabetes.”
