Human body temperature of 37°C has become history: the lower the body temperature, the worse the immunity? What does hypothermia mean
"The temperature is normal!" This is probably the most common phrase we hear these days.
During the epidemic, it is indispensable to measure body temperature every day. For a long time, 37°C is the normal body temperature in our cognition, but each time the body temperature is measured, it fluctuates between 35°C and 36.7°C.
There are also many studies that have found that human body temperature has dropped. What is going on?
1. Why is the human body temperature at 37 degrees Celsius?
37°C is set as the body temperature. How did this data come from?
Starting in the 1850s, German physician Wendlich collected data on the underarm body temperature of about 25,000 people and calculated a median value of 37°C. In this way, the standard body temperature of 37°C was recorded and gradually became common sense.
The strange thing is, why the middle value is 37℃, not 20℃, let alone 40℃?
It turned out that in ancient times, mammals were also cold-blooded animals . After continuous evolution, they became warm-blooded animals. A study published in "Nature", by speculating on the details of the fossil and some tiny pipes in the ear, analyzed that the inner ear structure suitable for the body temperature of warm-blooded animals appeared about 233 million years ago, and the constant body temperature also appeared at about this moment. .
Warm-blooded animals can regulate their own temperature and are more adaptable to complex environments.
There are a wide variety of fungi in nature, such as chytrid, bumblebee microsporidia, and group sprouts. For mammals, although there are more than 4,000 types of fungi that can be exposed, only about 500 can be infected, and most of them are not disease-causing. Among them, in addition to the immune system, the body temperature plays a crucial role.
The activity temperature of most fungi is between 4-30℃, and only a small part of fungi can survive in the environment above 37℃. That is to say, raising body temperature can kill more fungi, but raising body temperature also requires consuming more calories. In the end, humans seem to have found a balance between the two.
Of course, body temperature is not a fixed value, but a temperature range , including deep body temperature and surface body temperature. Clinically, body temperature refers to the mean deep body temperature. For example, the body temperature of the rectum is between 36.5°C and 37.7°C, which is closest to the deep body temperature; the body temperature of the armpit is between 36°C and 37°C; the body temperature under the mouth and tongue is between 36.3°C and 37.2°C.
2. The study found that the body temperature has dropped
However, as the environment changes, the normal body temperature of humans seems to drop.
In 2020, a research team from Stanford University School of Medicine found that since the Industrial Revolution, the body temperature of Americans has been dropping, from 37°C to 36.6°C in less than 200 years, a drop of 0.4°C.
In addition, a team of researchers from the University of California found that the body temperature of people living in a primitive tribe in South America was also dropping. Since 2002, researchers have recorded the body temperature of tribal people, when the average body temperature was 37 ℃. 16 years later, in 2018, their average body temperature was no longer 37°C, but dropped to 36.5°C. Among them, men's body temperature decreased faster than women's.
As for why, researchers at Stanford University believe:
One is related to the more suitable ambient temperature . Now a single air conditioner can solve the problem of cooling and heating. Human body temperature will also change with the change of living environment. In other words, human beings are still in the process of species evolution. .
The second is related to the reduction of inflammation in the human body . Inflammation will speed up the metabolism and increase the body temperature. As medical technology improves, inflammation decreases, and body temperature may also decrease. However, these claims are not universally accepted.
In addition, some people feel that it is related to the increased pressure in modern life and the reduction of physical activity. When people are in a state of stress, cortisol is continuously secreted, and it also stores fat while breaking down muscle, resulting in a continuous decrease in basal metabolic rate and a continuous decrease in body temperature.
3. Behind the drop in body temperature may be the weakening of immunity
Ishihara, a Japanese medical doctor, pointed out in his book "36.5 degrees determines health" that medical research has found that when the human body is in a sub-health state, for every 1 °C increase in body temperature, the immunity will increase by 5-6 times. Conversely, for every 1°C drop in body temperature, immunity decreases by more than 30%.
Why does an increase in body temperature increase immunity, and when body temperature decreases, immunity also decreases?
The reason may be related to the basal metabolic rate . Body temperature and basal metabolic rate are closely related, and a decrease in body temperature may indicate poor metabolism. If the metabolism is not good, the body is easily infected with viruses and bacteria, increasing the risk of illness.
In fact, there is currently no reliable research data to definitively answer whether a drop in human body temperature is more beneficial to health, more adaptable to the environment, or weaker .
Although the immune system will also increase as the body temperature rises, it is definitely unreliable to increase the body temperature to strengthen the immunity .
On the one hand, an abnormal increase in body temperature will speed up the rate of material metabolism and affect the normal function of the digestive system and nervous system. On the other hand, it also reduces the activity of natural killer cells (NK cells), weakening the body's ability to fight infection.
In fact, the drop in body temperature, whether good or bad, is a reminder for us and makes us pay more attention to body temperature. If there is an abnormal increase or decrease in body temperature in daily life, you should be vigilant and seek medical examination in time to find the cause.
References
[1] "36.8 ℃, when does the body temperature that is too stable appear? "Nature": The answer lies in the ears 200 million years ago". Academic latitude and longitude. 2022-07-21
[2]Myroslava Protsiv, Catherine Ley, Joanna Lankester, Trevor Hastie, Julie Parsonnet (2020) Decreasing human body temperature in the United States since the Industrial Revolution eLife 9:e49555 https://doi.org/10.7554/eLife.49555
[3] "The human body temperature of 37°C has become history, and immunity is actually...". China Medical Tribune. 2021-09-08
[4]The size of mammal ancestors’ ear canals reveal when warm-bloodedness evolved. R etrieved July 20, 2022 https://www.eurekalert.org/news-releases/959036
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