The accepted “normal” human body temperature of 98.6°F [37°C] has existed since 1851, when a German physician established that standard by surveying 25,000 people in one city.
However, recent analyses and surveys conducted by researchers at Stanford University suggest that average body temperature is now lower, and the reason is changes in human physiology over time, say researchers at Stanford University.
The Stanford team analyzed large amounts of temperature data from both men and women obtained during three time periods: 1862-1930, 1971-75 and 2007-2017. Overall, their sample included nearly 678,000 temperature measurements, which they used to create a model of change over time.
Some of their key findings include:
• The body temperature of men today is, on average, 0.59°C [1.06°F] lower than that of men born in the early 19th century.
• Women’s body temperature has dropped by 0.32°C [0.576°F] from the 1890s to today.
• Overall, the analysis found a 0.03°C [0.054°F] decrease in average body temperature with every decade.
So why has body temperature decreased since the Industrial Revolution? “The environment that we’re living in has changed, including the temperature in our homes, our contact with microorganisms, and the food that we have access to,” said Dr. Julie Parsonnet, a Stanford professor of medicine, health research and policy. She added that average metabolic rate, which indicates how much energy the body uses, has also declined over time, “Physiologically, we’re just different from what we were in the past.”
Because age, gender and time of day can all impact body temperature, however, the researchers do not currently advise updating the standard for all U.S. adults.