In 1851, a German doctor named Carl Reinhold August Wunderlich surveyed 25,000 people in a city and found that 37 degrees was the normal temperature of the human body. However, that has changed. A recent analysis suggests that average body temperaturein the USA since the 19th centurydecreased due to physiological changes. The authors of the new study also highlight possible causes for these changes.
Most recently, researchers in the UK calculated an average oral temperature of 36.6°C based on 250,000 temperature measurements on 35,000 people. Could this discrepancy be due to measurement errors? Researchers at Stanford University Medical Center in California examined this question in more detail.
To find out what really happened, Parsonnet and her team compared data sets from different periods. The first group included 23,710 Civil War Army veterans whose temperatures were measured between 1860 and 1940. “It took a long time to find a database from the 19th century that had body temperatures recorded,” says Parsonnet. The other data sets related to the periods from 1971 to 1975 and from 2007 to 2017. In total, the team analyzed 677,423 temperature measurements.
On average, American body temperatures have fallen by 0.03°C per decade. The average temperature of men born in the early 19th century was 0.59 degrees higher than that of men today. The data for women doesn't go back that far, but their body temperatures have fallen by 0.32°C since the 1890s.
This means that the average body temperature today is around 36.6°C, not 37°C as commonly believed.
Parsonnet provides two pieces of evidence that this negative temperature trend is real and is not just a result of older thermometers being unreliable. First, there isn't that much of a technological difference in thermometers between the 1960s and today.
Second, older people were found to have higher body temperatures than younger people measured in the same year, regardless of when that year was. One would also expect further data differences if the thermometers were less accurate.
“The most likely explanation, in my opinion, is that physiologically we are completely different people than we were back then,” says Parsonnet. “Our environment and the conditions in which we live have changed.” Thanks to vaccines and antibiotics, people are less likely to get infections these days, so our immune systems are less active.
This explanation suggests that the findings found should be transferable to other countries with advanced healthcare systems.
The study waspublished in the journal “E-Life”.
