When we hit our heads but develop no signs of concussion, we’re likely to breathe a sigh of relief, assuming we’ll be fine. But our bodies may be undergoing changes we can’t see or feel as the communities of microbes in our digestive systems shift in response to the trauma.
In both humans and mice, research shows concussions are associated with changes in the gut microbiome — a population of microorganisms that helps regulate digestion, behavior, the immune system, and other aspects of health. A team of Colgate professors and student researchers wondered whether nonconcussive head impacts could be linked with similar changes.
In a study that followed six Colgate football players through a season of play, the researchers found the first evidence that minor hits to the head can affect the diversity and composition of the gut microbiome. Their findings were published May 6 in the journal PLOS One.
“It’s not impossible to imagine that these kinds of events have whole-body effects, and it’s important to figure out how to reverse that,” says Aziz Zafar ’23, who majored in biology and is now pursuing a PhD in medical bioinformatics at Columbia University. “Scientists are working not just on probiotics, but also on exact cocktails of microorganisms that could replenish the gut after specific health challenges. Further characterizing how the head and the gut are linked is a step in the right direction.”
The study might also help identify a microbiome “signature” that makes it easier for doctors to diagnose brain injuries, even in the absence of other symptoms, explains Ken Belanger, the Russell Colgate Distinguished University Professor of biology.
“These findings are relevant not only to athletes,” he says, “but also to members of the military and anyone who experiences a nonconcussive head bump in a car accident or a slip on the ice.”
These findings are relevant … to anyone who experiences a nonconcussive head bump….
Ken Belanger, Russell Colgate, Distinguished University professor of biology
In the study, football players wore helmets fitted with Riddell monitors that tracked head impacts and their level of force — secured with the help of Zack Pelland ’23, a football player who majored in neuroscience and took the lead on designing the study. Pelland, who had interned with Riddell, obtained institutional review board approval and then collaborated with Colgate coaches and players. He learned more about how hits to the head were associated with microbiome shifts by using genomic sequencing to analyze 226 fecal samples provided by the players.
Through surveys submitted with each sample, the research team tracked how factors such as sleep, stress, and diet may have affected the athletes’ microbiomes. Then, Zafar and his mentor, biology and mathematics professor Ahmet Ay, used statistical modeling to remove those elements from the equation, isolating the effects of nonconcussive head impacts.
“This kind of careful adjustment is essential in human studies, where you can’t control every variable the way you can in a lab experiment,” Ay says.
The team found that certain bacteria populations in the microbiome — some of the same types that shift after severe brain injuries — became either more or less plentiful within the three days following a substantial nonconcussive impact and also cumulatively across the football season.
It’s too soon to say, though, whether nonconcussive head impacts caused the changes or what the fluctuations might mean for people’s health.
“We don’t know if these changes are positive and preventive, possibly helping with recovery, or negative, because there are prior data linking these organisms to neuroinflammation,” Belanger says.
Still, the findings could help resolve uncertainty about whether smaller head impacts even have the potential to meaningfully affect health, says Pelland, who is now pursuing an MD/PhD at the University of North Carolina-Chapel Hill.
“Shifts in these bacteria are hard to analyze at a population level because everyone’s gut microbiome is different,” he says. “The fact that we were able to see systemic changes after nonconcussive head impacts is interesting and worth exploring.”
Further insights will come from a larger football study Belanger conducted, which included 14 players who provided a total of 1,000 fecal samples, and his recently completed study involving Colgate women’s ice hockey players.
The initial study idea was conceived through the Robert H.N. Ho Mind, Brain, and Behavior Initiative (MBBI), which brought Belanger and Steve Chouinard, senior associate athletics director for health and performance, together to consider where their research interests might intersect. It was also facilitated by Riddell, whose leadership team includes several Colgate graduates.
“It’s so great to be at an institution that fosters these connections,” says Belanger, who chaired the MBBI committee at the time. “It’s been fun to work across areas of expertise and to have this collaboration lead to a really interesting outcome.”