Our body temperature drops and intestinal bacteria could be responsible for it

Over the past 150 years, researchers have seen the average human body temperature drop by more than half a degree Fahrenheit (-0.3°C). In a new study from the University of Michigan, scientists examining hospitalized patients with sepsis found that certain species of gut bacteria appeared to play a role in regulating body temperature, and it is speculated that these microbial alterations could be responsible for these long-term variations in body temperature.

In the mid-19th century, German physician Carl Reinhold August Wunderlich spent years collecting millions of body temperature measurements from thousands of patients. His work eventually found the average human body temperature is 98.6°F (37°C). Of course, that was just an average, with a normal body temperature range of 97.2-99.5°F (36.2-37.5°C).

Since then, many researchers have suggested that this average body temperature is a bit higher than what can typically be detected in most people. But a few years ago, a team at Stanford University claimed that Wunderlich’s original calculations were probably correct, and instead our modern measurements indicate that the average human body temperature has actually fallen over time. .

This search found the temperature of the modern human body was, on average, about 97.5°F (36.4°C), declining relatively steadily every decade over the past century. However, why this was happening was unclear and various hypotheses have been madefrom improvements in household heating and air conditioning reducing our overall metabolic rate to better health care resulting in lower population-wide inflammation.

In a new study by researchers at the University of Michigan Medical School, another hypothesis has been explored. This time, researchers investigated the role our gut microbiota might play in regulating body temperature.

To explore this, the study focused on hospitalized patients with sepsis. Previous research had shown that clinical outcomes for patients with sepsis could be predicted by body temperature trajectories during hospital admission. This investigation therefore asked whether the composition of the gut microbiome at the time of initial hospital admission could predict these body temperature trajectories.

Over 100 microbiomes of patients with sepsis were sampled upon admission to hospital and the study revealed distinct patterns of gut bacteria correlated with the trajectory of their body temperature during their hospital stay . In particular, high levels of Firmicutes bacteria were most associated with later high fever reactions.

By examining animal models, the researchers found that mice lacking the microbiome exhibited less extreme body temperature fluctuations when induced with sepsis compared to mice with normal gut bacteria. According to study leader Robert Dickson, the fluctuations in body temperature seen in the mice could be linked to similar bacterial families seen in the human sepsis cohort.

“We found that the same type of gut bacteria explained temperature variations in both our human subjects and our laboratory mice,” Dickson said. “It gave us confidence in the validity of our findings and gives us a goal to understand the biology behind this finding.”

So what does all this mean? According to lead author Kale Bongers, these findings are good evidence pointing to an important role gut bacteria play in regulating our body temperature. And changes in the microbiome due to diet over the past century may underlie the small drop in average human body temperature.

“While we certainly haven’t proven that changes in the microbiome explain the drop in human body temperature, we think it’s a reasonable hypothesis,” Bongers added. “Human genetics haven’t changed significantly over the past 150 years, but changes in diet, hygiene, and antibiotics have had profound effects on our gut bacteria.”

The study was published in the American Journal of Respiratory and Critical Care Medicine.

Source: University of Michigan