No. 177Health3 minviews 91
Published by GK Library Annex
Is 37°C Still the Right “Normal” Body Temperature?
A number set over 170 years ago, a slowly falling average, and readings that change with time and place
When people think of normal body temperature, 37°C usually comes to mind, but that number comes from records taken by a German doctor more than 170 years ago. Studies of people today have found a lower average, and even the same person's temperature changes with the time of day and where it is measured.
Where did 37°C come from?
In 1851, German physician Carl Wunderlich measured the armpit temperatures of 25,000 patients in Leipzig and set normal body temperature at 37°C. The normal range he recorded alongside it ran from 36.2°C to 37.5°C. But the range was forgotten, and only the number 37 survived, used as a standard for a long time.
Later studies in many countries usually reported a lower average. A 2017 analysis of records from more than 35,000 patients in the UK found an average oral temperature of 36.6°C.
Body temperature has been slowly falling
In 2020, a Stanford University team in the US compared about 670,000 temperature records from Civil War veterans in the 1860s, national health survey participants in the 1970s, and Stanford outpatients from 2007 to 2017. Even after adjusting for age, height, and weight, people born later had lower temperatures. The drop was 0.03°C for every decade of birth, so men born in the early 1800s ran 0.59°C warmer than men today.
The team suggested that fewer chronic infections such as tuberculosis, and living at comfortable temperatures thanks to heating and air conditioning, may have led the body to produce less heat. However, the cause has not been firmly established, and since the data are American, they may not apply directly to every country.
The same person varies, too
Body temperature rises and falls within a single day. In this study, too, readings taken later in the day were slightly higher. Temperature tends to drop a little with age, and women run slightly warmer than men. Heavier people also tended to read a little higher.
Where you measure matters as well. The armpit can read nearly 1°C lower than the mouth on average. So when measuring at home, rather than comparing with other people's numbers, it is more useful to learn your own usual temperature by using the same thermometer, on the same spot, at a similar time of day.
37°C is an average taken from armpits over 170 years ago; body temperature varies with the era, the time of day, and where it is measured.
Notes and references · Protsiv et al., eLife 9:e49555 (2020). Analysis of about 670,000 temperature records from three US cohorts: about 0.03°C drop per birth decade; describes Wunderlich's 37°C (range 36.2–37.5°C). US data only; the cause of the decline is the team's hypothesis
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