The copyright of the original article belongs to the WeChat public account
"Bring science home" all
Written by | Liu Liuqi
I don't know if you have a similar experience: it is the same temperature, but the feeling in spring and autumn is very different.
In spring, when we go out in the morning, the temperature is 10 degrees, and we walk in the sun in single clothes, and a layer of sweat soon appears on our foreheads; But in autumn, on the same 10-degree morning, we put on our coats and began to shiver as soon as the wind blew.
Some netizens analyzed that this is because autumn is summer before it, people are used to the heat, and the ratio of 10 degrees to heat is low; On the contrary, in the spring, the body has become accustomed to the cold, and the ratio of 10 degrees to the severe cold becomes a high temperature. While this is a slightly "emotional" statement, the scientific community shows some agreement: yes, the body does adapt to the temperature in this way.
图源:Kobie Complete
Before delving into the "different sensations of the same temperature", it is worth understanding the process by which the human body responds to cold.
When the temperature drops, the thermoreceptors on our skin are the first to pick up the change and relay signals to the hypothalamus. The hypothalamus is located on the ventral surface of the brain, below the thalamus, and although it weighs only 4 grams, accounting for 0.3% of the total brain volume, it has a strong ability to regulate human body temperature, feeding, reproduction and endocrine activities.
The red part is the hypothalamus|Source: Wikipedia
When the hypothalamus receives a cold signal, it generally directs the body to respond in two ways: the first is the constriction of blood vessels, especially peripheral blood vessels such as the skin. Vasoconstriction can reduce the heat exchange between the skin and the external environment, thereby helping the body to reduce heat loss. Secondly, we also increase heat energy by shaking the muscles, which is why people can't help but "shiver" in winter.
After learning about the two normal reactions of the human body to cold, we can monitor the degree of vasoconstriction and shivering to see if the human body becomes more cold-tolerant due to long-term exposure to cold.
图源：live science
Fortunately, there are already plenty of experiments in the scientific community that have given positive answers.
Researchers have found that Arctic natives have less vasoconstriction and shivering when exposed to cold than people living in the tropics. This is because they have become accustomed to the low temperature environment.
Some fishermen, who need to keep their hands in cold water frequently, are also "immune" to the cold. Experiments have found that if fishermen and ordinary people soak their hands in ice water at the same temperature, the temperature of fishermen's hands will be slightly higher, which is also the body's response to the cold.
Source: Harvard Health
In the spring, after a long winter, we became more tolerant of the cold like the inhabitants of the Arctic, so when the temperature warmed up slightly, it immediately became hot. In autumn, we have just passed the long summer, and like tropical residents, we are not "immune" to the cold, so as soon as the temperature drops, we are frozen.
This adaptation to cold is generally achieved through the regulation of the nervous system. However, if you are exposed to cold enough, the human body will even experience physiological changes related to "brown fat" and become more cold-tolerant
According to the color, the fat in the human body can be roughly divided into two types: white fat and brown fat.
橙色椭圆为脂滴，粉色椭圆线粒体，蓝色椭圆为细胞核｜图源：Everyday Health
White fat is about the same as the commonly known "fat meat", just like the middle school biology textbook says, its main role is to store energy. It is only when other "energy substances" are depleted that the body uses white fat cells. That's why it's so hard to lose weight, and you need a lot of aerobic exercise to get results.
图源：wikipedia
Brown fat cells are smaller than white fat cells, and there are many "energy generators" mitochondria inside the cells. So, when we feel cold, brown fat is able to release heat quickly and is a much more efficient "good fuel" than white fat. This means that if a person has more brown fat in his body, the more he can adapt to the cold and quickly reach a hotter body temperature in the bitter cold.
Scientists have found that when the human body is exposed to low temperatures for a long time, the body is more likely to produce brown fat; When the human body is exposed to hot environments for a long time, it is less likely to produce brown fat. So in the spring, we have more brown fat in our bodies than in the fall, which means that we have more "good fuel". This also explains why, again at 10 degrees, we feel warmer in the spring.
The researchers asked men to fall asleep at different temperatures every night, 24 degrees in the first month of A, 19 degrees in the second month of B, 24 degrees in the third month of C, and 27 degrees in the fourth month of D, and found that the amount of brown fat (shade of red) changed|Source: Reference 4
Of course, there are many other factors that affect the sensation: geographers believe that the direct point of the sun is closer to the northern hemisphere in spring, and the solar radiation is stronger, so it feels warmer; Psychologists have pointed out that people's different feelings about the same temperature in spring and autumn may also be due to "psychological suggestion".
However, there are still ways to better overcome the discomfort of changing seasons, such as exercise. When the temperature changes from hot to cold in autumn, exercise can cause white fat to turn into brown fat. When the temperature turns from cold to hot in spring, exercise can make our sweat glands more sensitive and release excess heat in time.
Get moving! Source: Internet
So exercise is always the right thing to do, so why not step out of the house and let the 10 degrees of spring get infinitely close to the 10 degrees of autumn?
Resources:
[1] Why kids don’t get as cold as adults do？https://www.youtube.com/watch?v=zpcI_g_zrpk
[2] Why a 65-Degree Day Feels Cold in Fall but Warm in Spring？
https://www.michiganmedicine.org/health-lab/why-65-degree-day-feels-cold-fall-warm-spring
[3] Here’s Why a 50-Degree Day Feels Colder in Fall Than in Spring
https://www.nytimes.com/2018/10/24/science/human-bodies-cold-weather-adjustment.html