So how did you get this basal body temperature? Recently, an article said that the normal body temperature has a downward trend. Is that really the case?
At present, the average standard body temperature we use is obtained by German doctor Carl Reinhold August Wunderlich after he conducted the world's first largest normal body temperature test in 185 1 year. At that time, he collected and analyzed the body temperatures of more than 25,000 people, and calculated that the basic normal armpit temperature of the human body was about 36-37 degrees. This temperature value has been used by all countries so far and has become common sense that ordinary people also know.
A study by Stanford University in the United States found that from19th century to modern times, human body temperature has been dropping slowly and continuously.
However, a recent study by Stanford University in California put forward the view that nearly 200 years ago, normal body temperature was within this range, but it may not be applicable now.
After analyzing American civil war veterans and other well-documented historical big data, researchers at Stanford University believe that the average temperature of that era is accurate, about 37 degrees for men. But in the past two hundred years, the average body temperature has been dropping slowly.
This study uses three big data for analysis. One is the file of American veterans from 1862 to 1930, and the other is the temperature record of 83,900 people. Due to historical reasons, this database only contains data on men. The other is the data collected from a large-scale national nutrition survey in the United States 197 1 to 1975, with a population of *** 1530 1. Another is Stanford University's own database, which collected 578,222 people's temperature data from 2007 to 20 17. The latter two have data on men and women. According to these data, the average body temperature of modern people is about 36.3 degrees Celsius [1]. From the end of 19 to the present, it has dropped by about 0.03 degrees Celsius every 10 year.
Of course, due to practical problems, there are many uncertainties in this study. For example, according to the ancient data from 1862 to 1930, it is hard to say that the average body temperature of these veterans can represent the basic body temperature of ordinary people in that year. After all, we can't know whether these people are healthy ordinary people, how to measure their body temperature and what thermometer they use.
Moreover, a person's temperature is a very complicated value, which is not always the same. The temperature in the afternoon is usually higher than in the morning. The body temperature of the elderly is lower than that of the young. The body temperature after exercise is higher than at rest. Height and weight also affect body temperature. The temperature and humidity of the environment and the physiological cycle of women will affect the body temperature. Therefore, the body temperature is not a constant and stable value, but always in a changing range.
But this figure still tells us more or less that the human body temperature has indeed dropped. Because this study analyzes the data of three different eras, it is found that the downward trend is continuous and linear. Although it is uncertain whether the degree of decline is related to factors such as race and region.
It is not surprising that the body temperature continues to drop slowly. Changes in the earth's environment may also affect changes in human body temperature. Just as our weight and height have changed greatly compared with our ancestors hundreds of years ago, it is not surprising that our body temperature has also changed.
There is no reliable research conclusion about the influence of hypothermia on human body.
But what does hypothermia mean to humans? Is it healthier and more adaptable to the environment? Or is it getting weaker? At present, there is no reliable research data to tell us which one.
Some articles quoted some documents that hypothermia will lead to decreased immunity, which may lead to an increase in the risk of illness. According to the existing research evidence, this statement is untenable. Indeed, some research articles have found that when studying the relationship between body temperature and anti-cold virus, rising body temperature helps to clear cold virus, and animals and people exposed to low temperature are more likely to be attacked by cold virus and have symptoms of respiratory infection. But such research is of little significance. First, study the extreme temperature phenomenon. For example, Yale University's research compared the nasal cavity temperature of 37 degrees and 33 degrees [2]. It is impossible for a person's temperature to drop to 33 degrees, at least not yet. Second, the ability to remove cold virus is not equal to the body's autoimmune ability. Such a slight drop in human body temperature does not lead to a low immune function.
Another way of saying it is that mild hypothermia is not only harmless, but also can prolong life and enhance disease resistance. Similarly, there is no detailed basis to support this statement. For example, animal experiments have found that lowering the central body temperature of mice by biological means by 0.5 degrees Celsius can prolong the life span of mice by 65,438+05% [3]. But this is a laboratory animal experiment and an observational study. After artificial hypothermia, basal metabolism will also decrease. It is difficult to determine whether the increase in life expectancy is due to hypothermia or basal metabolism. In addition, some observational studies on human beings have found that the average body temperature is 0. 149℃ and the annual mortality rate is 8.4% [4]. It seems that the higher the body temperature, the higher the death rate. But this does not mean that hypothermia can prolong life. Because ordinary people can also see the irrationality of this conclusion from this research article. Is it possible that high average body temperature is the cause of chronic infection? Is it possible that it is the cause of other chronic diseases? Is it possible to have a high basal metabolic rate?
In addition, the average basal body temperature of women is higher than that of men, but the average life expectancy of women is higher than that of men worldwide. It is difficult to exclude other very complicated interference factors in observational research, so it is difficult to draw causal conclusions. Therefore, it is too early to say that the drop of human body temperature will lead to the decline of immunity, or it will lead to the extension of life span, and there is no conclusive evidence to support it.
Then why on earth does the body temperature drop?
At present, we can only speculate that it may be caused by comprehensive factors.
For example, clothes of modern people are warmer than before. With the popularity of air conditioning and heating, we live in an environment where the temperature difference does not change much throughout the year, and we no longer need to pay a lot of energy to resist high temperature or cold, or because the lifestyle of modern people does not require physical activity as high as that of the ancients, it is not a problem to go out with a car or even stay indoors for a long time. These are all possible reasons.
But there is another possibility: because of the popularization of antibiotics and the improvement of environment and food hygiene, the probability of modern people suffering from infectious diseases has been greatly reduced. Compared with previous people, the probability of modern people being infected with infectious diseases such as tuberculosis, syphilis and smallpox is greatly reduced.
For example, a study conducted by the University of California in the United States on Tsimané people living in remote areas of Bolivia found that their basal metabolism at rest was much higher than that of people living in industrialized countries in modern society (about 20-40% higher), and nearly 65,438+00% of the energy consumed by their basal metabolism was used to deal with infection [3]. A high basal metabolic rate usually means a high body temperature. At the same time, the study also found that the body temperature of healthy adults in this area is also slowly decreasing year by year.
In the19th century, acute and chronic infections are very common, which is one of the biggest causes of death. For example, at that time, people who died of tuberculosis in Europe accounted for 1/4 of all deaths, and one out of every seven people died of tuberculosis [4]. In modern society, the infection rate of tuberculosis in many countries is very low. For example, in the United States, tuberculosis infection only accounts for 2.7/65438+ 10,000 people.
Suppose the basal body temperature of 1000 people is measured. If 1 1,000 people suffer from chronic or acute infection, their body temperature may be higher than that of ordinary people, which will also increase the average body temperature of this 1 1,000 people, and the data obtained may be higher than that of modern people who are not so infected.
Of course, it is also possible that the conclusion of German Wunderlich's temperature measurement at 185 1 is not reliable. Because now we don't know how he collected such a large amount of data and calculated and analyzed it in the era without computers. How was the body temperature measured at that time, whether it was measured under the armpit or in other parts, and how to eliminate interference factors, such as different body temperatures in different parts, different body temperatures in the morning and evening, different body temperatures in four seasons, and different body temperatures in women during ovulation. It is not an easy task to get the average healthy body temperature of the population by removing these interference factors, especially in the era of 185 1, where the technical means are backward and the modern statistical concept does not exist. Furthermore, compared with the thermometers used in19th century, the thermometers used in modern society have much higher accuracy and more stable reading temperature. This may also be a reason.
On the other hand, this study by Stanford University also found that the average body temperature of people has been declining since the 1970s, which supports the conclusion that the body temperature has been declining slowly since the 9th century. Moreover, it is found that the data of 185 1 year show that there are reasonable differences in basic average body temperature at different ages and different heights and weights, suggesting that this body temperature data is not randomly compiled, but is indeed the measured result.
Therefore, there may be many reasons for the slow decline of human body temperature, and there is no clear conclusion as to which is the most important factor.
But one thing is certain, fever is still fever. Although everyone's normal body temperature will be different, if the body temperature exceeds your normal body temperature range, it is a fever and you need to see a doctor if necessary.