A study of retired martial arts and collision sports athletes found that athletes with extensive disruption of the blood-brain barrier tended to experience more severe cognitive decline. Those with more severe cognitive decline also tended to have a greater systemic inflammatory burden, including an increased proportion of circulating monocytes. The paper is scientific translational medicine.
Combat and collision sports such as boxing, martial arts, American football, rugby, ice hockey, wrestling, and lacrosse often involve strong impacts between players and with the ground and equipment. Contact sports such as soccer, basketball, and handball also involve physical contact, but violent collisions are not the focus of the games.
Athletes who participate in these sports experience repeated blows, impacts, or rapid movements to the head. This is known as repetitive head trauma or repetitive head impact exposure. This includes both diagnosed concussions and minor impacts that don’t immediately cause noticeable symptoms.
In the short term, head injuries can cause headaches, dizziness, balance problems, poor thinking, memory problems, difficulty concentrating, sleep problems, and mood changes. Some athletes may experience symptoms for weeks or months after a concussion. Repeated head impacts over many years can increase the risk of developing persistent cognitive, emotional, and neurological difficulties.
These include problems with memory, attention, concentration, and the ability to plan and organize tasks. Some people develop delayed thinking, confusion, poor judgment, or progressive decline in cognitive function. In some cases, repeated head trauma may be associated with Parkinson’s disease, a group of symptoms similar to those seen in Parkinson’s disease.
Study author Chris Green and colleagues wanted to investigate the long-term effects of repetitive head trauma on the relationship between blood-brain barrier integrity and cognitive function. The blood-brain barrier is a selective protective layer formed by tightly connected cells in brain blood vessels that controls which substances can pass from the bloodstream to the brain. Disruption of the blood-brain barrier allows normally restricted substances and immune cells to enter brain tissue, which can cause inflammation, fluid leakage, swelling, and neurological dysfunction.
Study participants were 47 former combat and collision sports athletes who had been involved in contact sports for at least 5 years and had not been exposed to repetitive head trauma, and 15 control participants. The former combat and collision sports athletes included 33 former rugby union players, eight boxers, three Gaelic footballers, two soccer players and one American football player. Controls were 3 rowers and 12 non-athletes. The average age of participants was 40 years.
Study participants completed a clinical interview designed to establish their level of exposure to repetitive head trauma. They also underwent diagnostic procedures for traumatic encephalopathy syndrome (a clinical condition associated with significant exposure to repeated head impacts), an assessment of cognitive impairment (MoCA Screening), and an assessment of symptoms of depression (using the Beck Depression Inventory). Additionally, he underwent brain magnetic resonance imaging and provided a blood sample.
Results showed that 17 participants had widespread blood-brain barrier disorders, even though all participants had stopped regular participation in contact sports for more than a year. These individuals tended to show more severe cognitive decline compared to participants with less extensive disruption of the blood-brain barrier. In retired athletes, higher proportions of circulating monocytes, an indicator of greater systemic inflammatory burden, were associated with stronger cognitive decline.
The study authors also found changes in immune-related pathways, particularly the complement system. The complement system is an important part of the immune system. It is composed of more than 30 blood proteins that quickly “supplement” the ability of antibodies and white blood cells to eliminate pathogens, cause inflammation, and destroy foreign cell membranes. These changes to the complement system may contribute to the damage seen around blood vessels in the brains of the study participants.
Overall, the findings suggest that repetitive head trauma may cause long-term blood-brain barrier impairment and persistent inflammation, both of which may be involved in later cognitive problems and contribute to accelerated cognitive decline.
This study contributes to scientific understanding of the health effects of practicing combat and collision sports. However, we note that the observational design of this study does not allow definitive causal inferences to be drawn from the results.
The paper, “Blood-brain barrier disruption, traumatic encephalopathy, and cognitive decline in retired athletes”, was written by Chris Green, Declan Brennan, Shayda Milroux, Ruairi Connolly, Geoffrey O’Callaghan, Avril Reddy, Geoff Henderson, Gelgoo Polcolove, Adam McGlinchey, Nicole Hanley, Siobhan Hutchinson and James FM. Meany, Michael Farrell, Sarah L. Doyle, Aron Freedman, Colin P. Doherty, and Matthew Campbell.
