"Normal body temperature!" This is probably the most common thing we've heard lately.
During the epidemic, it is indispensable to take the temperature every day. All along, 37 °C is the normal body temperature of the human body 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?
First, why is the human body temperature at 37 degrees Celsius?
37 °C is set to the human body temperature, how did this data come about?
Starting from the 1850s, the German physician Wendrich collected data on the underarm temperature of about 25,000 people and calculated the median value of 37 ° C. In this way, the standard body temperature of 37 ° C was recorded and slowly became common sense.
Curiously, why is the median value 37 °C, not 20 °C, let alone 40 °C?
It turns out that in ancient times, mammals were also cold-blooded animals, and after continuous evolution, they became thermostatic animals. A study published in Nature, by speculating on the details of fossils and some tiny pipes in the ears, analyzed that about 233 million years ago, the inner ear structure suitable for the body temperature of thermostatic animals appeared, and the constant body temperature also appeared at about this moment.
Thermostatic animals are able to regulate their own temperature and are more able to adapt to complex environments.
There are many kinds of fungi in nature, such as Chytrid frog, Bumblebee microsporidium, Andes sporangia. For mammals, although they can be exposed to more than 4,000 kinds of fungi, only about 500 species can be infected, and most of them are not pathogenic. Among them, in addition to the immune system, there is also body temperature.
Most fungi have an active temperature between 4-30 ° C, and only a small number of fungi can survive in environments above 37 ° C. That is, raising body temperature can kill more fungi, but increasing body temperature also requires consuming more calories, and eventually, in between, 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 body surface body temperature. Clinically, body temperature refers to the average deep body temperature. For example, the body temperature of the rectum is between 36.5 ° C and 37.7 ° C, the closest to the deep body temperature; the body temperature under the armpit is between 36 ° C and 37 ° C; and the body temperature under the oral tongue is between 36.3 ° C and 37.2 ° C.
Second, the study found that the body temperature of the human body may have dropped
However, as the environment changes, the normal body temperature of humans seems to have dropped.
In 2020, a team of researchers at Stanford University School of Medicine found that since the Industrial Revolution, American body temperature has been declining, from 37°C to 36.6°C, down 0.4°C in less than 200 years.
In addition, a team of researchers at the University of California also found that the body temperature of people living in a primitive tribe in South America is also declining. Beginning in 2002, researchers began recording body temperatures in tribal populations, when the average temperature was 37°C. 16 years later, by 2018, their average body temperature was no longer 37°C, but had dropped to 36.5°C. Among them, men's body temperature drops faster than women's.
As for why, researchers at Stanford University argue that:
First, it is related to the more suitable ambient temperature, and now an air conditioner can solve the problem of refrigeration and heating, and the human body temperature will also change with the changes in the living environment, that is, in fact, human beings are still in the process of species evolution.
The second is related to the reduction of inflammation in the human body, which will speed up the speed of metabolism and increase body temperature. With the advancement of medical technology, 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 of modern people's life and the reduction of exercise. When people are in a stress state, cortisol is constantly secreted, decomposing muscles and storing fat, resulting in a continuous decline in the basal metabolic rate and a continuous decrease in body temperature.
Third, behind the decline in body temperature, it may be the weakening of immunity
Japanese medical doctor Ishihara Kiyoshi pointed out in his book "36.5 degrees determine health" that medical research has found that when the human body is in a sub-healthy state, every 1 ° C increase in body temperature, immunity will increase by 5-6 times. Conversely, for every 1°C drop in body temperature, immunity is reduced by more than 30%.
Why body temperature rises, immunity rises; What if the body temperature drops and so does the immunity?
The cause 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. Poor metabolism, the body is prone to infection with viruses and bacteria, increasing the risk of illness.
In fact, whether the decline in human body temperature is more conducive to health, more adaptable to the environment, or becomes weaker, there is no reliable research data to clarify the answer.
Although the body temperature will increase and the immunity will also rise, it is certainly unreliable to strengthen the immunity by increasing the body temperature.
On the one hand, an abnormal increase in body temperature can speed up the rate of substance metabolism, affecting the normal functioning of the digestive system and nervous system. On the other hand, it also reduces the activity of natural killer cells (NK cells) and weakens the body's ability to resist infection.
In fact, whether the body temperature drop is good or bad, it is a reminder for us and also makes us pay more attention to body temperature. If in daily life, there is an abnormal increase or decrease in body temperature, you should be vigilant, seek medical examination in time, and find the cause.
Resources
[1] "At 36.8°C, when does the body temperature that is stable enough to not work appear?" Nature: The Answer is in the Ears of 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] "Human temperature of 37 °C has become a history, 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 from https://www.eurekalert.org/news-releases/959036
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