The Silent Epidemic: How Traumatic Brain Injury Affects the Microbiome

The Silent Epidemic

Traumatic brain injury (TBI) is considered a “silent epidemic” because many of the resulting acute and chronic deficits in cognitive, motor, and somatosensory functions may not be obvious to observers.  

Moderate to severe TBI is a major cause of injury-induced death and disability, with an annual incidence of approximately 500 in 100,000 people affected in the United States. Approximately 80% of all TBI cases are categorized as mild head injuries. But these numbers are likely underestimated due to the incidences of TBI for which a person does not seek medical care.  

How Does a Brain Injury Have Anything to do with the Gut? 

An important but under-addressed element of brain injury is the disruption of gut health and microbial function.  

The 2 most common ways in which trauma influences the gut are: 

• Directly—specifically injuring the gut
• Systemically—via an inflammatory response.  

Communication between the brain and the microbiome occurs via the Gut-Brain Axis (GBA). The GBA is composed of a complex network of signaling pathways as well as direct neural mechanisms. Our gut is connected to the brain via the GBA, so changes in gut commensals can influence the brain, and conversely, trauma in the brain can impact the intestinal microbial community. For example: 

• Several studies have found that stroke injury alters microbial composition and decreases diversity in the gut.  
• Alterations in gut microbial populations have been demonstrated in mice receiving a closed-head mild TBI.  

The clinical findings of these studies suggest that TBI alters the gastrointestinal microbiome and creates dysbiosis in the absence of other injuries, resuscitation, antibiotics, and analgesics. 

The Science Says… 

Microbial diversity on admission in severely injured patients predicts a variety of clinically important outcomes. For example: 

• Reductions in intestinal microbial diversity have been linked to increased mortality in critically ill patients
• The evolution of the traumatic lesion directly correlates to changes in the GI microbiome 

In a prospective, observational study in adult patients (n=67) who sustained severe injury, fecal specimens collected on admission showed acute decrease both in alpha and β-diversity of microbes. A larger brain lesion size was associated with a significant reduction in α-diversity.  

Specifically, a larger brain lesion was found to be associated with greater decreases in levels of Firmicutes (overall beneficial bacteria) and an increase in Proteobacteria (more likely to be pathogenic bacteria).  

High-Risk Populations for TBI 

Study findings could have far-reaching implications for athletes and veterans. While less dramatic in clinical presentation, concussions are a frequent occurrence in contact sports such as: 

• Football  
• Hockey  
• Lacrosse  
• Soccer  

And female athletes are twice as likely to experience concussions as compared to men. Increasing evidence suggests that athletes may sustain multiple concussions over the course of their career.  

Another significant population is soldiers suffering from blast-related injuries, with one in six soldiers returning from combat deployment in Iraq meeting the criteria for concussion.  

These particular groups may experience shifts in microbial diversity that could influence lifelong health, brain function, and mood and behavior as a result. 

So, What Can You Do to Support Both the Microbiome and the Brain? 

Our ecological community of commensal, symbiotic and pathogenic microorganisms have a great influence on our homeostasis, resilience and even survival from severe injury. Given the growing data, microbial diversity must be addressed and prioritized in the acute and chronic phase of TBI treatment and recovery.  

Now that we understand the effects of TBI on the microbiome, and the fact that the brain and the microbiome affect one another, taking a high-quality, 100% spore-based probiotic can help in maintaining a healthy microbiome. At the end of the day, a balanced microbiome can make all the difference in healing from a TBI.