The average human body temperature has been falling steadily since the mid-19th century, and scientists don’t know why. A new study suggests a key factor that may play a role in this: gut microbes.
Looking at data from patients hospitalized with sepsis – where the body reacts in dangerously extreme ways to infection – as well as tests on mice, the researchers behind the study looked at the relationship between gut bacteria , temperature changes and health outcomes.
This choice of patients with sepsis is deliberate, as the disease can lead to various temperature fluctuations in the body that are often linked to a person’s chances of recovering from it.
“We know that the temperature response is important in sepsis because it strongly predicts who lives and who dies,” says microbiologist and immunologist Robert Dickson from the University of Michigan.
“But we don’t know what drives this variation and whether it can be changed to help patients.”
The team studied gut bacteria samples taken from 116 people with sepsis, finding that there were wide variations in the microbiota – and that the variations correlated with changes in patients’ temperature trajectories.
Bacteria from the Firmicutes phylum were most closely associated with higher fever. These bacteria produce substances important for the growth and health of the body and influence the body’s immune response and metabolism.
While it’s not enough to show that gut bacteria are the reason our insides have gotten colder over the past 150 years, it’s an interesting hypothesis – and it shows how our gut microbiome is linked to body temperature. .
“You could say that our patients have more variation in their microbiota than in their own genetics,” explains internist Kale Bongers, also from University of Michigan. “Two patients are more than 99% identical in their own genomes, while they may have literally 0% overlap in their gut bacteria.”
In further tests on healthy mice with and without the bacterial microbiome, lower basal body temperatures were observed in animals without the bacteria – while antibiotic treatment also reduced body temperature in mice.
Additionally, in humans and mice, the same family of bacteria appeared to be associated with temperature fluctuations. The next step is to look at more samples from a wider range of people and determine what biological mechanisms underlie this relationship.
With more research, we may be able to develop ways to alter the gut microbiome specifically to affect body temperature – and this, in turn, could improve the outlook for people with conditions such as sepsis.
“There’s a reason the temperature is a vital sign,” says Bongers. “It is both easy to measure and gives us important information about the inflammatory and metabolic state of the body.”
The research was published in the American Journal of Respiratory and Critical Care Medicine.