The inhabitants of Bolivian indigenous Amazons are helping to reinforce recent findings that normal body temperature, around 37 ° C or 98.6 ° Fahrenheit, may no longer be as normal.
The tsimane horticultural-forage people of the South American nation experienced a half-degree, average, drop in body temperatures over a decade and a half, anthropologist Michael Gurven and colleagues reported on Oct. 28 in Science Advances
The new finding echoes the mid-grade drop in average body temperature reported earlier this year in a Stanford University study of three U.S. population cohorts over 157 years. In that research, normal body temperature dropped 0.03 ° C per decade.
Body temperature serves as a kind of substitute for the basal metabolic rate or the amount of calories needed to keep the body working while at rest. Higher rates were related to shorter lifetimes and lower body mass. Body temperature, which also reflects circadian rhythms, immune function, the presence or absence of disease, as well as room temperature, is affected by age, sex, and time of day (SN: 10/2/17).
Sign up to receive the latest from Science News
Headlines and summaries of the latest Science News articles, delivered in your inbox
More than a matter of curiosity, lower temperatures could be indicative of a change in basic human physiology, says Jill Waalen, an epidemiologist at the Scripps Research Translation Institute in La Jolla, California, who did not participate in either study. And this could mean a rethinking of what constitutes a fever: a timely issue, given the use of temperature controls to detect COVID-19.
Improving lifestyles and access to health care have reduced overall rates of infectious diseases and inflammation and could be the reason for temperature drops. But making that connection has definitely proved difficult, says Gurven, of the University of California, Santa Barbara.
The 37 ° C normal was derived in the mid-1800s by physician Carl Wunderlich based on his study of about 25,000 Germans. More recent studies, in addition to the Stanford study, suggest that today the average body temperature is low. However, these studies have largely focused on the populations of relatively rich countries.
Instead, the new research focuses on indigenous people living in the Bolivian Amazon. The people of Tsimane live in villages with no running water or electricity and subsist largely on rice, bananas and vegetable root cassava. Rapid changes in the community in recent decades include increased access to store-bought food and antibiotics.
Gurven, who co-directs the Tsimane Health and Life History Project, and colleagues examined 17,958 temperature measurements of 5,481 teens and adults in Tsimane and found that the average mid-grade body temperature drop had taken only 16 years, from 2002 to 2018. The reason for the fall is more difficult to determine. It could be based on levels of inflammation or infection rates and even room temperature on a given day.
“The newspaper has been an opportunity to explore everything that has been happening (in this group) over the last 20 years,” Gurven says.
To find a cause of the decline, the team analyzed several variables related to temperature and environmental health, including trends in respiratory diseases or parasitic infections over time. The team found that Tsimane people’s respiratory illnesses decreased over time, but other health conditions such as parasitic infections and blood diseases remained common. In general, the researchers found no connection between the decrease in mean body temperature and any individual variables or combinations of variables.
Gurven and colleagues still suspect that lower average body temperature could arise as a result of increased access to medications, such as painkillers or antibiotics, or better nutrition, although more research will be needed to prove it.
Even without a clear explanation, this growing body of evidence suggests that normal body temperature could be considered more appropriate as a person-to-person range, not as a fixed value in the population, says Waleed Javaid, an infectious disease specialist on Mount Sinai. . New York City Downtown Health Network. Studies such as Bolivian research, he points out, could help public health experts develop a new range of normal body temperatures.