This article is from the public number: The Academy of Sciences (ID: kexuedayuan) , author: Duan Yunfeng (Institute of Microbiology, Chinese Academy of Sciences)
This time, becauseFor the epidemic, almost all the people in the country are taking body temperature. Recently, foreign people have also joined the team to take body temperature. Many countries have begun outbreaks and have started body temperature monitoring.
During the period of isolation, the author measured the body temperature for 14 days, basically all of which were 36.5 ° C, while the group friends in the same group were basically at this level, not exceeding 37 ° C.
Did we always think that the normal body temperature of 37 ℃ has become history?
Human body temperature has been falling?
Really! On January 7, 2019, Julie Parsonnet, a professor at Stanford University School of Medicine in the United States, published a (Julie Parsonnet) In a study, they found that since the 19th century, the average body temperature of adults has continued to decline, falling by 0.4 ° C in less than 200 years, from 37 ° C to 36.6 ° C. In 2017, a study conducted in the United Kingdom analysed 250,000 body temperature records of more than 35,000 patients and found that the average body temperature of the British was 36.6 ° C.
This survey in the United States has a larger amount of data and a long time span. They used data from three cohorts, totaling more than 500,000 people, including: Civil War Alliance veterans (23,710 people; measurement date 1860 ~ 1940) , National Health and Nutrition Examination Survey I (15,301 people; 1971 ~ 1975) and Stanford University’s translation research comprehensive database (150,280 people; 2007 ~ 2017) . According to statistics, the temperature of men born at the beginning of this century is 0.59 degrees Celsius lower than that of men born at the beginning of the 19th century, which means a steady decline of 0.03 degrees Celsius every ten years. Women’s body temperature changes have similarly declined, with a drop of 0.32 degrees Celsius since the 1890s.
Men’s body temperature change from 1840 to 1940 (picture from: Reference 1)
Temperature changes of white and black men and women (picture from: Reference 1)
Who controls our temperature?
The exact reason for the decline in human body temperature has not yet been stated, and there are many factors affecting body temperature.
A person is a constant temperature animal. Theoretically, the body temperature can be kept constant. However, due to the different physical conditions of each person, the body temperature is actually a range of change.
Regulation of body temperature is controlled by specific brain regions in the brain, primary (SI) and secondary (SII) Somatosensory cortex may cause temperature-related sensations. (aMCC) also involves sensory processes, including the pleasantness or discomfort of encoding temperature sensations, Role in Autonomic Nerve Response. Back cingulate cortex (PCC) is also related to the response to temperature changes.
Regional brain area (picture from: Reference 11)
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It is reported that these areas of the brain will also be inactivated by continuous changes in body temperature. For example, during long periods of heating and cooling, the activation of relevant areas of the brain that regulate body temperature will fail, and body temperature regulation will fail, such as excessive body temperature. Heat shots.
The external factor that can explain changes in body temperature may be global warming. At present, global temperature has been rising. According to data released by the World Meteorological Organization, the global average temperature in 2018 was 0.38 ° C higher than the average value from 1981 to 2010, which is
Global average temperature anomalies from 1850 to 2018 (compared to the average value from 1850 to 1900) (Image from: Reference 5)
China is one of the countries with the most pronounced warming. From 1951 to 2018, China ’s annual average temperature increased by 0.24 ° C every 10 years, and the rate of temperature rise was significantly higher than the global average over the same period. I do n’t know if the changes in Chinese body temperature are the same as those in the United States. In the past few months, a large range of body temperature measurements have been taken across the country. The dedicated scientific research team should have seized the opportunity to collect national data to see the Chinese. According to this temperature trend, maybe the temperature of the Chinese is lower than that of the United States.
The annual mean temperature anomaly between China and Asia from 1901 to 2018 (compared to the average value from 1981 to 2010) (picture from: Reference 5)
The possible mechanism for the drop in body temperature caused by climate change is that the increase in external air temperature may help the body save a part of energy consumption. The body no longer needs so much energy to maintain body temperature, and the basal metabolism will decline accordingly. Of course, the body temperature will also decrease. Will follow. Of course, this is only speculation and has not been verified.
In addition to changes in temperature, people ’s living environment is actually undergoing drastic changes, especially in the past one or two hundred years. With the development of industry, human living habits and living environment have undergone tremendous changes, such as the use of air conditioners. Changes in living conditions and drastic improvements in sanitary conditions may affect body temperature.
Temperature regulation may also be related to microorganisms. When a person is infected with a pathogen, they will respond to the infection by raising their body temperature, which is what we call “fever.” Some scientists believe that with the improvement of health, medical care and dietary conditions, modern people will not be susceptible to various inflammatory diseases as in the past, and naturally they will not have to raise their body temperature in order to kill pathogens. Therefore, human body temperature also decreased.
However, the author thinks this explanation is inconsistentThe reason is that the temperature at which the pathogen is killed has not changed, and there is no evidence that the temperature that the pathogen can tolerate has decreased. With climate warming, the temperature resistance of pathogens should increase.
What is the relationship between microorganisms and body temperature?
Reduction of intestinal microbes and acceleration of human body temperature drop?
The acceleration of industrialization has also led to changes in intestinal microorganisms in the human body.
The use of antibiotics, the strengthening of sanitation facilities, and medical production to eliminate pathogenic bacteria have saved countless lives and changed people’s lifestyles. Decreasing the proportion of natural foods, increasing the diet of processed foods, the use of infant formula, modern medicine, and sanitation facilities can all significantly change the composition of the intestinal flora.
Influence of industrialization on human microorganisms (Image source: KELLIE HOLOSKI / SCIENCE, 8)
Gut microbes have been symbiotic with humans for millions of years and have undergone thousands of generations of cooperation. Now, compared to the “traditional” flora, the “industrial” flora has lower microbial diversity and fewer.
The current lifestyle of human beings, while helping people resist pathogenic bacteria, is also harming the normal microorganisms of the human body. Only 5 days of ciprofloxacin can seriously damage the intestinal flora and kill a large number of bacteria, and it may take weeks or even months to recover to the level before medication, and it may not be completely recovered.
People eat almost all aseptic food and water. This is good. While sterilizing, not providing bacteria, this reduces the number of bacteria in the human body. Studies have found that changes in lifestyles, drinking water and food changes in Nepal and Haza in Africa have led to significant changes in the composition of the intestinal flora.Food and diet interfere with and exacerbate the disappearance of certain bacteria.
In the 1990s, people have noticed that if the microorganisms in animals are removed, their temperature will drop. For example, studies have found that the temperature of sterile animals is generally about 2 ° C lower than that of bacteria. If antibiotics are used to kill intestinal microorganisms in animals such as rabbits, mice, and pigs, their temperature will drop by 1 ° C to 2 ° C.
The temperature of sterile animals is lower (picture from: Reference 9)
The reduction in body temperature of sterile animals is passive. Many animals can also actively regulate their body temperature. For example, during hibernation, their body temperature will decrease and their metabolic rate will decrease. Studies have investigated the body temperature of hibernating animals such as squirrels, brown bears, and their intestinal flora.
It was found that as the body temperature decreases, the gut microbes of these animals also change: for example, the bacterial diversity decreases, the relative abundance of pathogenic bacteria such as Pachybacteria and Salmonella decreases, and the number of Bacteroides .
Unlike squirrels, Verrucomicrobia bacteria in the intestinal flora of hibernated brown bears have almost completely disappeared. This may be because Verrucomicrobia bacteria (for example, the famous Ackermannia that feeds on intestinal mucus) at temperatures as low as 20 ° C Can grow under the next. Perhaps, these bacteria actively withdrew from the animal’s gut in order to maintain the health of the host, and they could not stand the long hibernation.
Microbial changes of hibernating animals (picture from: Reference 6)
Adding microbes can raise body temperature?
About 30 years ago, some people have done experiments, they can regulate the body temperature of animals by regulating intestinal microorganisms.
They inoculated mice that were kept sterile. The first group was inoculated with 100 million E. coli, and the second group was inoculated with the treated intestinal mixture. They are then reared for a few weeks and tested for their temperature.
As a result, it was found that inoculation with E. coli had no significant effect on body temperature. The use of intestinal microorganisms will cause rapid temperature rise (Figure 1 below) . Compared with the sterile control, the temperature of mice inoculated with intestinal microorganisms increased by 0.5 ° C. (Figure 2 below) The average temperature was 0.4 ° C higher than that of sterile mice. In other words, inoculation of intestinal microorganisms can completely restore the lowered body temperature.
Inoculation with intestinal microorganisms can raise body temperature (picture from: Reference 10)
Is it the same for humans?
There is still little research in this area. Perhaps by increasing microbial diversity, increasing certain microorganisms can raise body temperature. I hope that interested researchers can give us evidence.
However, there is some potential evidence in this regard. For example, in 2019, scientists from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences published a report in the Cell Report, exploring the role of intestinal flora in activating brown fat. Brown fat has good heat-producing ability. This kind of non-trembling heat can raise body temperature.
UCP11 gene is involved in temperature regulation (picture from: Reference 7)
Brown fat is the “super star” in obesity research in recent years. There is a large piece of brown adipose tissue in the infant’s scapula. Its job is to absorb the burning energy of nutrients and produce heat to regulate body temperature. As the baby grows up, the brown fat gradually decreases, and the adult body may disappear.
In 2009, it was first demonstrated that adults also retained a little brown fat, especially in the neck, collarbone, kidney, and spinal cord, but they were not very active and were activated when the body became cold. Numerous studies have confirmed that brown fat is more difficult to find in obese and diabetic people than in lean and healthy people.
Brown fat distribution Labros Sidossis / Rutgers University (Image source: http://www.proteanservices.com/)
The researchers found that when they administered antibiotics to “remove enterobacteria”, the mice’s brown fat was damaged and their ability to produce heat decreased. In mice without enterobacteria, the expression of UCP1 gene cannot be increased, and the level of browning of white fat is also reduced. In 2018, a study showed that if mice were orally administered a metabolite of common bacteria, butyrate, this damage was partially reversed: butyrate significantly increased brown fat levels and increased energy in antibiotic-treated mice Consumption, and partially reversed the loss of heat production due to depletion of the microbiota.
This shows that it is still very promising to adjust the intestinal flora to increase body temperature. At least supplementation with the microbial metabolite butyrate has seen a trend. Perhaps after supplementing with specific microorganisms, the lowered body temperature can make up .
A person weighing 70KG can produce 70 watts of heat per hour with intestinal microorganisms?
Some people have seriously discussed the use of microorganisms to raise body temperature. Professor Rosenberg, Eugene of the University of Tel Aviv in Israel published an article in 2016 that explored the relationship between intestinal microbes and body temperature in detail. Like all cells, microorganisms produce heat as long as they live, and they convert heat more efficiently than animals.
In general, the heat generation of microorganisms is inversely proportional to the growth rate: the faster the growth, the lower the heat generation rate per unit weight.
How much heat can microorganisms produce? According to reports, after measuring the growth of an anaerobic bacteria using glucose as a substrate using a microcalorimeter, the specific heat generation rate of the bacteria was calculated to be 247 mW / g. The time it takes is about 4 hours. Considering that the average doubling time of mammalian intestinal bacteria is about 3 hours, the calorific value of bacteria in animals is expected to be 168 ± 11 mW / g.
Because 1W = 0.24cal / sec, the estimated average heat production of intestinal bacteria is 168mW / g, which is equivalent to 0.0403cal / sec per g of bacteria. The weight of the resident bacteria in the human colon is approximately 300g dry weight (NIH Human Microbiome Project 2012 estimate) , which will produce about 12cal / sec or 43kcal / h. Assuming that heat is dissipated in a person weighing 70 kg and no heat is lost, intestinal bacteria will increase the person’s body temperature by about 1.0 ° C / h.
In contrast, oneThe total measured heat generated by an individual at rest is about 1W / kg, which is 70W for an average person, which is equivalent to 60kcal / h. This accounts for almost 70% of the body’s heat in the body when it is at rest. That is to say, under theoretical conditions, the theoretical energy produced by intestinal bacterial metabolism can account for so much of human energy.
Of course, this is only a theoretical guess. The actual situation may be different. However, we can make it clear that microorganisms seem to be involved in many tasks in maintaining body temperature.
It is very possible to regulate body temperature through the intestinal flora
The lowering of human body temperature may be harmful to human health. The optimal reaction temperature of various enzymes secreted by the human body is mostly 37 ° C. A decrease in body temperature may reduce the metabolic efficiency of the human body, increase energy intake, and may also reduce human immunity and increase the risk of inflammation. Studies have found that dieting lowers body temperature, but at the same time lowers the metabolic rate and increases fat storage. After dieting, it is not conducive to weight loss.
At present, there is little research on the impact of lower body temperature on human health. If the lower body temperature does affect health, then it is of great significance to regulate the intestinal microorganisms to raise the body temperature. How to adjust? Here are a few tips:
Avoid the abuse of antibiotics, which will substantially eliminate gut microbes.
Avoid clean living habits. Decreasing the number and type of human microorganisms may cause a decrease in body temperature.
Supply a variety of foods. Because there are many types of human microorganisms, different foods are needed to satisfy their appetite. It is recommended to have more than 12 food types per day and more than 25 food types per week.
Avoid ultra-processed foods as much as possible. The characteristics of these foods are that no raw materials can be seen, and a lot of preservatives, preservatives, and flavoring agents may be added to them. These ingredients may harm the intestinal microorganisms.
Appropriate foods with high dietary fiber content. Dietary fiber is a food favored by intestinal microorganisms.
Many outdoor activities, there are a large number of microorganisms in the environment, and these microorganisms may be members of human microorganisms. At the same time, temperature changes in the environment can also helpThe body’s temperature regulation mechanism is normal.
References:
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This article is from the public number: scientific compound (ID: kexuedayuan) , author: Duan Yunfeng (Institute of Microbiology, Chinese Academy of sciences)