Today a body temperature of around 37 ° C is considered normal. However, normal human body temperature can fluctuate by several degrees. Factors such as age, environment, weight, height, gender and even time of day play a role in the thermometer readings. But what body temperature has been considered normal in the past? According to a study published in eLife's Open Access Journal, human body temperature is lower today than it was two centuries ago. The authors of the thesis argue that from 1851, when the first systematic records were collected, the temperature of the human body gradually decreased.
What temperature is considered normal?
The gold standard of 36.6 ° C is based on the work of the German doctor Karl Reinhold August Wunderlich, who in 1851 collected and averaged the first data from 25,000 patients. Researchers at Stanford University School of Medicine carefully examined old and new human body temperature data to find out if differences can be explained by devices and methods that have been used in the past.
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During the study, a team of specialists compared temperature readings from a number of sources from 1862–2017. In total, the researchers analyzed the performance of more than 677,000 subjects. Based on the evidence, they found that the average temperature in men fell to around 36.3 ° C. The average temperature in women also dropped, although not so significantly, to around 36.6 ° C. Scientists have documented that body temperature has been falling steadily since the mid-19th century.
The researchers also confirmed some of Wunderlich's early results, including that young people's body temperature at rest is higher than that of adults and that of women is slightly higher than that of men. Taking into account the temperature measurement method and all known data on the instruments used, the researchers concluded that our body really cools down. But why?
Why is human body temperature lower today than it was 160 years ago?
Despite the fact that determining the reason for the cooling is beyond the scope of the study, the authors proposed several possible explanations. As Dr. Wunderlich carried out the measurements, the average life expectancy was only 38 years and the average body temperature was 36.9 ° C. In addition, chronic infections were widespread in those years, from tuberculosis to syphilis. Because average body temperatures tend to decrease with age and increase with infection, young people may have chronic illnesses and their bodies may be hotter.
Do not forget about medical achievements – since inflammatory processes often lead to an increase in body temperature, the use of anti-inflammatory drugs such as aspirin can also play the role of a gradual "cooling". Unlike a normal 19th century citizen, most of us today spend most of our lives in an air-conditioned environment that can affect thermometer readings.