No one likes to freeze; Thus, he becomes frustrated when François Haman tries to use the cold temperatures of volunteers for his studies on the health benefits. He does not blame them. Haman, who studies thermal physiology at the University of Ottawa in Canada, says the human body is weak in the face of cold. He says:
I have done studies in which people were exposed to a temperature of 7 degrees Celsius, which is not too cold. Few people can stand it for 24 hours. (Those people were even fully clothed: gloves, hats, boots and socks, however, could not stand the cold).
People try to keep the air in a comfortable range by smoothing the temperature changes indoors so that they do not tremble or sweat. You can easily turn the heater on or off when you feel uncomfortable. But you may not need to deal so much with the thermostat.
Some of the reasons for lower heat consumption are obvious: About 47 percent of American homes burn natural gas for heat and 36 percent use electricity, which in the United States continues to be largely fossil fuel. There may also be other reasons for the cold: health factors that physiologists like Hamann may have begun to discover.
Haman says these extremes were not part of life before industrialization. The human body coped with cold in winter and heat in summer, and these experiences probably contributed to metabolic health.
Researchers know that the body reacts when cold. New fat appears, muscles change, and a person’s level of comfort increases with prolonged exposure to cold. But the consequences of these changes for modern human health (and whether we can use the effects of the cold to improve health) are unclear.
Some researchers are trying to understand how cold-induced changes in fat or muscle can help prevent metabolic diseases such as diabetes. Some researchers also suggest that coping with the cold is easier said than done. For Haman, these are useful scientific questions; Because freezing has been one of the oldest threats to our existence. He says:
For me, the cold is one of the most exciting stimuli, because it’s probably the biggest challenge a human being can have. Although the heat is challenging, I will survive as long as I have access to water and shade. The cold is quite the opposite. If you can not work together, if you do not have the right equipment, if you do not have the right knowledge, you will not survive.
Understanding how the body changes in response to such a powerful, old adversary provides clues as to how the body acts in the cold and how to take advantage of the potential benefits of the cold.
Haman starts each day with a cold bath. The cold stimulates the body to release hormones called catecholamines, which are involved in the fight or flight response. “I feel very strong and alert,” he says. “It works like coffee for me.”
But these hormones are stress hormones, and they do not hide the truth: humans are not well adapted to the cold. Humans do not have fur and have long, slender arms and legs. Blood must travel long distances to warm them. When it is very cold, the body sacrifices the blood flow that goes to these extremities to maintain the central temperature.
At rest, humans produce up to 100 watts of heat. But if you lose a lot of heat through the skin, the energy balance is upset. Under these conditions, the body commands that more heat be generated. The first response is behavioral: you try to find the heat: approaching a fire, going under a blanket or a cup of hot drink. The second answer is physiological, and it starts when the skin temperature drops a few degrees: you are shaking. Your teeth will probably grind first and then the rest of your body will tremble. You are contracting and you have basically no control over your body.
Other animals, such as mice and squirrels, are not so poorly designed. They have a lot of brown fat or adipose tissue that burns calories to generate heat. Biologists call this trick “vibration-free heating.”
Initially, scientists thought that brown fat and the non-vibration heat-producing process were specific to rodents; But in 2009, The New England Journal of Medicine published three separate discoveries that confirmed that adult humans also had brown fat and could therefore produce heat without trembling.
Haman has since shown that cold tolerance can teach the body to store more brown fat. In a study published in 2013, he asked participants to wear special cold clothes for two hours a day, five times a week for a total of four weeks. Inside the clothes, water was circulating at 10 degrees Celsius. The dress was cold and uncomfortable, but the compromise doubled people’s brown fat, which appeared around the spine, adrenal glands and pelvic floor muscles.
Brown fat does not stay still when it appears and actively replaces vibration to generate heat. “Everything is compensated by heat without vibration,” says Haman.
In the study participants, wearing cold clothes also tripled the amount of brown fat that was active or how much it burned. The vibration rate decreased by about 10 to 20% after adapting to the cold. In other words, participants became accustomed to the cold by producing more brown fat, which in turn made them feel more comfortable at lower temperatures without the need to shake.
Then in 2019, Haman conducted another study. He recruited seven men to spend seven days in the cold. They were immersed in water at 14.5 ° C until the clavicle bone for up to an hour each day, until their central temperature dropped to 35 ° C. They were then dried and reheated slowly. “It’s basically a tough hour,” says Haman. “But in seven days you will be a different person.”
Participants were able to withstand a cold for an hour longer than before the experiments before they began to shiver. Their vibration intensity was reduced by an average of 36%.
Other laboratories around the world have tried to find out if brown fat has other benefits. In rodent studies, it has been found that activating brown fat at cold temperatures regulates the levels of fatty acids and glucose. This finding has led some researchers to suspect that this tissue could protect against inefficient glucose processing in diabetes and fatty acid processing in obesity.
To date, some studies in adults have linked the presence of brown fat to weight loss and normal blood sugar. But it is not a simple suggestion to tolerate a little cold, add some brown fat and then lose weight. The story is a little more complicated.
After the discovery of brown fat in 2009, Juris Hooks, a diabetes researcher at the University of Maastricht in the Netherlands, was curious about its role in controlling blood sugar. His team used people with type 2 diabetes to study cold adaptation.
An important feature of type 2 diabetes is insulin resistance, in which the organs of the body absorb less blood sugar. Participants endured six hours of cold, just shivering at the border, for 10 days. Their sensitivity to insulin, a key hormone used to control blood sugar, improved by an average of 43%. This improvement was comparable to the effects of a 12-week exercise program. “We thought it was a great result,” Hawks recalls. The cold seemed to alter the insulin response. But there was no clear association with brown fat activity. “The cold activated it, but not too much.”
So, the Hawks team did another study. In a study published in March 2021, they repeated the experiment, but to completely prevent vibration, they did things like raise the temperature and give participants extra clothing if needed. Under these conditions, adaptation to mild cold did not improve glucose regulation or fat metabolism.
The results of these two studies show that muscle changes are more important for diabetes than brown fat. Muscle cells change in the cold. In cold conditions, the proteins responsible for transporting glucose fuel to muscle cells appear to migrate out of the cell. Hawks thinks the change may help the body process more clogs, either because of mild or imperceptible vibrational contractions or because of other muscle processes.
Hawks says colds are really effective, but increased insulin sensitivity in people with diabetes through exposure to cold is not associated with brown fat.
Other studies have shown that muscle is 50 times more responsible for metabolizing glucose than brown fat because the body has a lot more muscle. Haman also agrees that muscle cells may be important in regulating blood sugar. “If I do this during the day, I’ll probably consume more fat than coffee, glucose and fatty acids,” he says as he moves his biceps.
So far, the evidence seems to support Haman and Hawks’ conjecture that cold adaptation is beneficial to humans, but there is still much ignorance. For Haman, the next step is to try to consider dietary restrictions.
He wants to see in future studies how exposure to cold and calorie restriction affects weight loss. One group limits their diet, the other group does so in the cold, and the other group only exposes itself to the cold. This study will examine their weight loss. But, of course, Haman says hiring volunteers will be difficult: “Think how easy it is to hire people to study who are going to be exposed to the cold for nine weeks.”
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