Non-concussive head impacts (NHIs) sustained during American football correlate with changes in gut microbiome diversity and composition both acutely (three days following a head impact event) and cumulatively across a competition season.
Key Findings
Results
NHI exposure correlates with changes in microbial diversity and composition three days following a head impact event.
Short-term changes in the gut microbiome were analyzed for correlation with head impact events in collegiate American football players
The association was observed acutely at a three-day post-impact timepoint
Both microbial diversity metrics and compositional changes were affected
Head impact exposure was monitored using objective measurement tools tracking head acceleration events (HAEs)
Results
Athletes' gut microbiomes changed significantly across the competition season, with mixed-effects modeling indicating cumulative NHIs contribute to this change.
Long-term changes in the microbiome were analyzed for correlation with cumulative head impact events across the full competition season
Mathematical mixed-effects modeling was used to examine the contribution of NHIs and other clinical factors to microbiome changes
Cumulative NHI effects were identified as contributors to season-long microbiome shifts
The study monitored gut microbiome composition, head impact exposure, and a breadth of clinical and behavioral factors throughout the season
Methods
The study population consisted of collegiate American football players monitored across a full competition season.
Participants were collegiate-level American football players
Monitoring occurred across a competition season
Data collected included head impact exposure, gut microbiome composition, and clinical and behavioral factors
NHIs were defined as hits to the head or head acceleration events that do not generate clinically detectable symptoms and are unlikely to meet diagnostic criteria for mild traumatic brain injury (mTBI)
Background
NHIs, defined as head impacts not generating clinically detectable symptoms, have not previously been linked to microbiome alterations prior to this study.
Prior research had established that TBIs and brain-related diseases and disorders can alter gut microbiota composition
No previous studies had linked microbiome alterations specifically to non-concussive head impacts
NHIs are a significant health concern among at-risk groups including athletes and military personnel
NHIs are unlikely to meet diagnostic criteria for mild traumatic brain injury (mTBI), distinguishing them from concussions
Conclusions
The study provides evidence for both acute and long-term links between NHIs and gut microbiome changes.
Both short- and long-term changes in the microbiome were analyzed for correlation with head impact events
Results provide 'strong evidence for a link between NHIs and changes in the diversity and composition of the gut microbiome'
The authors emphasize the importance of monitoring head impacts 'including those that do not generate clinical symptoms'
Mathematical modeling was used to disentangle the contribution of NHIs from other clinical factors
What This Means
This research suggests that hits to the head that don't cause concussion symptoms — called non-concussive head impacts (NHIs) — are associated with measurable changes in the gut microbiome of college football players. The researchers tracked players throughout an entire football season, collecting gut microbiome samples and measuring head impacts using sensors. They found that within three days after a head impact event, the diversity and bacterial composition of players' gut microbiomes shifted. Additionally, by the end of the season, players' microbiomes had changed significantly overall, and statistical modeling pointed to the cumulative buildup of these sub-concussive hits as a contributing factor.
The gut microbiome — the community of trillions of microorganisms living in the digestive tract — plays an important role in overall health, including immune function, mental health, and inflammation. While scientists already knew that serious traumatic brain injuries could affect the gut microbiome (through a biological communication pathway sometimes called the gut-brain axis), this study is the first to show a similar connection with hits to the head that don't produce any obvious symptoms. This is significant because NHIs are extremely common in contact sports and among military personnel, and they often go unrecognized and unmonitored.
This research suggests that even impacts considered 'sub-clinical' — below the threshold for a concussion diagnosis — may have biological consequences that extend beyond the brain. The findings highlight the potential value of monitoring all head impacts in contact sports, not just those resulting in concussions, and open new questions about whether microbiome changes following NHIs could contribute to longer-term health effects seen in athletes and others with repeated head impact exposure.
Pelland Z, Zafar A, Ay A, Belanger K. (2026). Non-concussive head impacts sustained during American football correlate with changes in gut microbiome diversity and composition.. PloS one. https://doi.org/10.1371/journal.pone.0345651