1 week, 5 days ago

Over the past 100 years, the temperature has become higher and higher, but the human beings have become colder and colder 




 
 picture source: pixabay 
 
 
 the body temperature of normal people is 37 ℃, which is the physiological common sense that we have been told and believed since childhood. Published in 
 
 eLife 
 
 pointed out that the value was out of date. 

In 1851, Carl Reinhold August Wunderlich, a German doctor, put forward that the standard of body temperature for human health is 37 ℃ after repeatedly testing the axillary temperature of 25000 patients. But according to the latest study, 
 the average body temperature of Americans has dropped to 36.6 ℃ 
. 

Researchers at Stanford University looked up medical records of US soldiers from the civil war period (1860's) until their retirement and compared them with those of two modern medical databases. They confirmed that for more than 100 years, the body temperature of 
 American men 
 has been steadily decreasing, with a decrease of 
 0.59 ℃ 
. Of course, the body temperature of 
 American women 
 is no exception, with a decrease of 
 0.32 ℃ 
 in the same period. 

Julie parsonnet, the study's co-author, said the findings showed that while humans are transforming nature, they are also changing themselves. "We're not only getting taller and heavier, we're getting colder," she said. "I'm not sure about the link between hypothermia and health, but the result is that the human body is changing as never before, and this change is closely related to what we've done in the past 150 years." 


 cooling trend in 150 years 


However, parsonne believes that it may be caused by many factors, such as the improvement of clothing warmth, the progress of indoor temperature control technology, and the depersonalization of lifestyle. The most important point may be that the number of patients with 
 infectious diseases has decreased 
 - in contrast, modern people are less likely to suffer from infectious diseases such as tuberculosis, syphilis and gum disease. 

According to parsonne, residents in developed countries and regions such as the United States often live for a long time in what scientists call the "thermal neutral zone". Because the temperature of the neutral zone is constant, the human body does not need to adjust the metabolism system to regulate the body temperature. Although air conditioning in the office can make some people shiver in the summer, it's better than spending the night in a cave with only a few degrees Celsius. However, it is not clear whether the modern people who are closer to the 19th century lifestyle will have higher body temperature. 

Studies of tsiman é, an indigenous people living in the lowlands of Bolivia, have shown that infection does increase average body temperature. In a paper published in 2016, anthropologist Michael gurven of the University of California, Santa Barbara, who was not involved in the study, pointed out that the energy consumed by infection accounted for 10% of tisman's resting metabolism, and that metabolism was positively correlated with body temperature. However, he also found that the body temperature of 
 healthy tesimans also decreased by 
 between 2004 and 2018, which indicates that more in-depth research is needed on the causes of the temperature drop. 

Parsonne speculated that lower metabolic rates and body temperature might be a good thing for human health. She hopes to find more connections between the two in the future. 

In this study, parsonne's team compared three different data sets: 83900 body temperature records of American Civil War veterans from 1862 to 1930, 15301 body temperature records from 1971 to 1975 from the first national health and Nutrition Survey (NHANES I), and 578222 body temperature records from 2007 to 2017 from Stanford's stride. Data on the body temperature of American women in the 19th century were not available, but researchers collected the body temperature records of American women in the latter two data sets. The final results showed that 
 in the study time range, the body temperature of both men and women decreased steadily. 



 defects and disputes 


Philip mackowiak, emeritus professor of medicine at the University of Maryland School of medicine, who was not involved in the study, wondered whether the data could really go back to the civil war. "I just don't think we can test the authenticity of the research results." Because there are so many unknown variables in this data set, such as the health status of these veterans, the location of temperature measurement and the temperature measuring instrument used, he said. 

Even Dr. Wunderlich's results, published in 1851, are controversial, mccoweck said: Although the sample size of the study is large, we still have no way to know whether his temperature measurement methods are consistent, and how he analyzed so much data in that era when computers did not appear. And "different parts of the body have different temperatures," he added. Generally speaking, the kidney temperature is the highest, while the epidermis temperature is the lowest. What's more, he said, "normal body temperature is not constant, it has a range of fluctuations." In addition, the body temperature will be different at different times of the day. For example, the body temperature in the morning will be lower. At the same time, due to physiological cycle and other reasons, the average body temperature of women will be higher than that of men. 

Parsoney acknowledged that there were some limitations in the data during the civil war, such as whether the body parts selected for body temperature measurement were strictly recorded according to the measurement results. They were worried until parsoney and colleagues observed similar trends in two other datasets, she said. When the years of birth of veterans were used instead of the years of measurement, the trend of hypothermia still existed. This shows that the trend can not be explained by the type of thermometer and other factors. Moreover, the distribution of age, height and weight in the data set is in line with the expectation, which shows that the conclusions drawn by 
 can stand the test of 
. 

Frank R ü HLi, of the Institute of evolutionary medicine at the University of Zurich, said the findings were compelling even if the data were flawed. "It's very interesting to look at human body temperature data over a span of more than 150 years," he said. "It gives us a valuable opportunity to observe short-term changes in human physiological characteristics. “

Although the debate about normal human body temperature continues, there is a consensus among experts: whether normal body temperature changes or not, the standard of 
 fever will not change. McCormick said that it is generally believed that an adult's temperature above 37.7 ℃ is a fever. "Body temperature can help to judge the condition, and by comparing it with the normal value, we can roughly know the severity of the condition. "He said. He also mentioned that for patients with bacteria, a temperature below normal is often more dangerous than fever. Tracking a patient's temperature can also allow doctors to assess whether you are getting better or how well you are treating them, McCormick added, although "your own feelings are the most important."

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