Why did human body temperature drop?

Why did human body temperature drop?

Author: Fan Gang

What is the human body temperature? In the past, many biology textbooks would write 37℃. However, in the past two years, people have often measured their body temperature. If you recall the results of the measurements, most people will find that their daily body temperature is always lower than 37℃, and even hovers around 36.5℃.

Why are body temperatures in textbooks higher than what people actually measure today?

The "standard body temperature" of 37℃ was the result of research by a German doctor named Carl Wunderlich in 1851. At that time, he measured the body temperature of more than 20,000 test subjects millions of times and finally concluded that 37℃ is the average body temperature of a person under normal circumstances. However, in 1992, Philip McCoveyack, a professor of medical history at the University of Maryland, found that the thermometer Wunderlich used at the time was not accurate. Professor McCoveyack redesigned the experiment and concluded that the average sublingual standard body temperature of healthy adults under the age of 40 is 36.8℃.

The medical community has long debated whether the standard human body temperature is 37°C or 36.8°C. However, in the past two years, scientists have published a new study that analyzed the temperature measurement data of the past 150 years and found that the average human body temperature is not fixed, but is slowly decreasing. The average rate of decrease is 3/1000 degrees per year. In other words, it decreases by 0.3°C every century[1].

This is strange. You said that human body temperature rises when you have a fever and drops back down when the fever subsides. This is normal. But as a species, the average temperature of humans should be constant. The body temperature of cats is 39℃, and the body temperature of chickens is 41℃. Every creature has a normal body temperature, so why is the human body temperature slowly dropping?

The paper gives a guess: perhaps it is because human living conditions have improved.

Everyone knows that if a person is sick or has inflammation, he or she may have a fever. The so-called fever is actually a defensive measure of the human body, which is the human body actively raising the body temperature. Although a higher temperature makes people feel uncomfortable, weak, and unclear, the bacteria in the human body feel even worse. When the body is in a feverish state, the human body can better defeat harmful bacteria.

Having said that, not all bacterial infections and inflammations will cause fever. In daily life, many people suffer from chronic inflammation, such as chronic pharyngitis, chronic rhinitis, etc., and many people are accidentally infected by bacteria, have diarrhea after eating unclean things, etc. However, these inflammations and infections are not very serious, so the human body will only slightly increase the temperature, and people will not feel that they have a fever.

In the past, people lived in poor conditions, the environment was unsanitary, and there were not as many useful medicines as today, so it is very likely that most people carried harmful bacteria and chronic inflammation. In other words, most people had a slight fever. Doctors at that time did not know this, so they took the average temperature of these people as the normal temperature.

Now that hygiene and medical care are gradually improving, fewer and fewer people have low-grade fevers, so the measured body temperatures are becoming lower.

Of course, this is just a guess by the researchers and has not been proven. But now you know that human body temperature is indeed slightly lower today than in history. Maybe there will be some other interesting changes in humans in the future.

References:

[1] https://elifesciences.org/articles/49555

This article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.