It is true that normal body temperature has been declining in recent years. A 2017 study in the U.K. included some 35,000 adults whose average body temperature appeared to be 97.9 degrees Fahrenheit, and a 2019 U.S. study found that normal average body temperature among adults tested in California was even lower: 97.5. Research also has shown that over as few as 16 years, normal body temperature of native people in the Bolivian Amazon declined to about 97.7 degrees.
According to Michael Gurven, Ph.D., a professor of anthropology at the University of California, Santa Barbara and his team of investigators, in less than two decades, average body temperatures declined among the Bolivian natives by the same levels as those seen in the U.S. over approximately two centuries. These findings came from observations of nearly 5,500 adults and were adjusted for factors that might affect body temperature, such as ambient temperatures and body mass.
Dr. Gurven wrote that declines in normal body temperature have been seen in the U.S. since the Civil War. He says, “We’ve experienced fewer infections over time due to improved hygiene, clean water, vaccinations and medical treatment.” [
Some possibilities: Dr. Gurven said it could be that people today are in better physical shape than those in the past, so their bodies might be working less to fight infection. Or greater access to antibiotics and other treatments has shortened the duration of infections. His team found that a respiratory infection seen early in the study resulted in a higher body temperature than when the same respiratory infection occurred more recently.
Postdoctoral researcher, Thomas Kraft, Ph.D., a member of Dr. Gurven’s team, suggested that one possibility for the change is that our bodies “don’t have to work as hard to regulate internal temperature because of air conditioning in the summer and heating in the winter.” He added that while body temperatures in Tsimane natives in Bolivia “do change with time of year and weather patterns, [these people] still do not use any advanced technology for helping to regulate their body temperature. They do, however, have more access to clothes and blankets.”
Bottom line: average normal body temperature appears to have dropped, so don’t worry if yours is lower than 98.6.
Andrew Weil, M.D.
Michael Gurven et al “Rapidly declining body temperature in a tropical human population.” Science Advances, October 28, 2020, DOI: 10.1126/sciadv.abc6599