Athletes with a history of sprained ankle show reduced gut bacteria diversity, say scientists from Japan in a new study

Lateral ankle sprains (LASs) are extremely common injuries that can have long-lasting consequences if not treated properly, including alterations in brain function, psychological stress, and chronic pain. In a recent study, scientists from Ritsumeikan University, Japan found that athletes with a history of LAS had lower richness of gut microbiota compared to that in healthy athletes, providing evidence that LAS, although a local injury, can affect global health.

Lateral ankle sprains (LASs), which occur when the ligaments on the outside of the ankle are stretched beyond their limits, are among the most common injuries in a wide variety of sports and daily activities of living. Unfortunately, most people tend to minimize the severity of a LAS and disregard it as a minor problem—one that does not require any medical treatment. The consequences of this neglect can be long-lasting ankle pain, weakness, and disability from which some never fully recover.

However, LASs can affect much more than just the ankle. Studies have shown that, following a LAS, individuals suffer from various sensory–perceptual and motor–behavioral impairments. From problems in sending signals from the brain to the lower extremities to changes in the structure of the cerebellum (the part of the brain involved in motor control), it is becoming more and more evident that a LAS has global consequences on a person’s health.

Considering that gut microbiota—the microorganisms that live in our digestive tract—is known to change in response to brain injury or pathologies of the nervous system, could it be that LAS affect our gut microbiota as well? A team of researchers from Ritsumeikan University, Japan, led by Dr. Masafumi Terada, sought to answer this question in a recent study published in Research in Sports Medicine.

They theorized that the altered brain functions caused by LASs could have a negative impact on the gut microbiota. To test this out, the researchers recruited male participants from collegiate athletic teams. They selected 32 athletes with a history of LAS for the case group and 18 athletes with no history of LAS or any other musculoskeletal injuries, as the control group. After receiving fecal samples from the participants, the researchers used DNA extraction assays to analyze the composition of the gut microbiota.

They found that athletes with a history of LAS had less biodiversity in their gut microbiota compared to that of the control group. While the precise underlying mechanisms behind these microbiota alterations remain unknown, the researchers speculate that they could be closely related to the neural effects of LAS, increased psychological stress, and/or to a possible “communication” pathway between gut microbiota and the joints, which could cause the selective proliferation of certain bacteria that promote inflammation.

One thing, however, is certain: LAS constitutes a neuromechanical condition that impacts multiple body systems and has an effect on global health. Therefore, it is essential that we gather further evidence on how serious and far-reaching the consequences of LAS can be so that treatments can be improved. “Considering intestinal microbiota as an important element of health in LAS is an innovative idea with significant scientific, medical, and socioeconomic consequences,” highlights Dr. Terada. “Associations between LAS and the intestinal microbiota would constitute a significant step forward in developing strategies meant to prevent long-term negative consequences,” he adds.

The team envisions that, in the future, gut microbiome will be incorporated as an element of personalized management in LAS. For example, the abundance of Bacteroides Fragilis and Ruminococcus Gnavus (bacteria that produce proinflammatory compounds) could be used as a biomarker to identify LAS patients with an incomplete recovery from the injury. “Our study provides a focused area for future research to examine the predictive and diagnostic qualities of gut microbiota diversity in LAS and determine if assessing gut microbiota richness can improve upon the current medical care,” explains Dr. Terada. From a more proactive standpoint, the team theorizes that the external modulation of gut microbiota through interventions might represent a way to control the body’s inflammatory response and restore normal functioning of the central nervous system.

Let us hope this study would pave the way to a more thorough understanding of the effects of LAS on global health, allowing more people to seek timely care for sprained ankle injuries.

Title of original paper: Altered gut microbiota richness in individuals with a history of lateral ankle sprain
Journal: Research in Sports Medicine
DOI: 10.1080/15438627.2022.2036989.
Publication date: February 11, 2022 (online)

About Dr. Masafumi Terada from Ritsumeikan University, Japan

Dr. Masafumi Terada is a lecturer at Ritsumeikan University where he holds academic appointments in College of Sport and Health Science. He earned his Ph.D. from the University of Toledo, USA. His primary area of research deals with ankle and knee injuries to reduce the long-term consequences of these conditions over the lifespan. He studies these injuries from a multifactorial perspective using diverse tools ranging from laboratory-based outcome measures of biomechanics and motor control to patient-generated outcome measures. He has over 50 publications and over 70 conference presentations. He is also a member of the National Athletic Trainers’ Association.

Funding information

This study was funded by the Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists A (#17H04756).