The average human body temperature has dropped in the United States since the 19th century, according to a study published in the journal eLife.
In 1851, German physician Carl Reinhold August Wunderlich established that the standard human body temperature is 98.6 degrees Fahrenheit, but several studies have called that figure into question over the last few years, including a 2018 study published in the Journal of General Internal Medicine that found the average normal body temperature could be closer to 97.7 degrees Fahrenheit.
For the study published in eLife, researchers analyzed body temperatures from three U.S. data sets covering the following historical periods: 1862 to 1930; 1971 to 1975; and 2007 to 2017. They studied 677,423 temperature measurements from these data sets.
They found that the body temperature of men born in the 2000s is on average 1.06 degrees Fahrenheit lower than that of men born in the early 1800s. They also found that the body temperature of women born in the 2000s is on average 0.58 degrees Fahrenheit lower than that of women born in the 1890s. These figures correspond to a decrease in body temperature of 0.05 F every decade.
The researchers said that the decrease in body temperature could be due to a reduction in metabolic rate, which is the amount of energy the body uses, and changes in the environment in which humans live.