In a new study, researchers found that since the 19th century, the average human body temperature in the United States has dropped.
The research was conducted by a team at the Stanford University School of Medicine.
The team says what everybody grew up learning, which is that our normal temperature is 98.6, is wrong.
That standard of 98.6 degrees Fahrenheit was established by German physician Carl Reinhold August Wunderlich in 1851.
Modern studies, however, have called that number into question, suggesting that it’s too high.
A recent study, for example, found the average temperature of 25,000 British patients to be 97.9 F.
In the study, the team explored body temperature trends. They analyzed temperatures from three datasets covering distinct historical periods.
The earliest set, compiled from military service records, medical records and pension records from Union Army veterans of the Civil War, captures data between 1862 and 1930 and includes people born in the early 1800s.
A set from the U.S. National Health and Nutrition Examination Survey I contains data from 1971 to 1975.
Finally, the Stanford Translational Research Integrated Database Environment comprises data from adult patients who visited Stanford Health Care between 2007 and 2017.
The researchers used the 677,423 temperature measurements from these datasets to develop a linear model that interpolated temperature over time.
They found that the body temperature of men born in the 2000s is on average 1.06 F lower than that of men born in the early 1800s.
Similarly, they observed that the body temperature of women born in the 2000s is on average 0.58 F lower than that of women born in the 1890s.
These calculations correspond to a decrease in body temperature of 0.05 F every decade.
The team says that temperature changes since the time of Wunderlich reflect a true historical pattern, rather than measurement errors or biases.
The decrease in average body temperature in the United States could be explained by a reduction in metabolic rate or the amount of energy being used.
This reduction may be due to a population-wide decline in inflammation. Inflammation produces all sorts of proteins and cytokines that rev up the metabolism and raise the body temperature.
One author of the study is Julie Parsonnet, MD, professor of medicine and of health research and policy.
The study is published in eLife.
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