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A study involving retired combat and collision sports athletes found that those with extensive blood-brain barrier disruption tended to experience worse cognitive decline. Those with worse cognitive decline also tended to have a greater systemic inflammatory burden, including an increased proportion of circulating monocytes. The paper was published in Science Translational Medicine.
Combat and collision sports, such as boxing, martial arts, American football, rugby, ice hockey, wrestling, and lacrosse, involve frequent forceful impacts between athletes or with the ground and equipment. Contact sports, such as soccer, basketball, and handball, also involve physical contact, although powerful collisions are less central to the game.
Athletes participating in these sports repeatedly experience blows, jolts, or rapid movements of the head. This is known as repetitive head trauma or repetitive head-impact exposure. It includes both diagnosed concussions and smaller impacts that do not produce immediate or noticeable symptoms.
In the short term, head trauma may lead to headaches, dizziness, balance problems, slowed thinking, memory difficulties, reduced concentration, sleep disturbances, and mood changes. Some athletes continue to experience symptoms for weeks or months after a concussion. Over many years, repeated head impacts may be associated with an increased risk of persistent cognitive, emotional, and neurological difficulties.
These include problems with memory, attention, concentration, and the ability to plan or organize tasks. Some people develop slower thinking, confusion, impaired judgment, or progressive cognitive decline. In some cases, repeated head trauma is associated with parkinsonism, a group of symptoms resembling those seen in Parkinson’s disease.
Study author Chris Greene and his colleagues wanted to explore the long-term consequences of repetitive head trauma on blood-brain barrier integrity and its link to cognitive functioning. 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 into the brain. When the blood-brain barrier is disrupted, substances and immune cells that are normally restricted may enter brain tissue more readily, potentially contributing to inflammation, fluid leakage, swelling, and impaired neuronal function.
Study participants were 47 former combat and collision sports athletes with at least 5 years of exposure to contact sports who were no longer exposed to repetitive head injuries, alongside 15 control participants. The former combat and collision sports athletes were 33 former rugby union players, 8 boxers, 3 Gaelic footballers, 2 soccer players, and 1 American football player. The controls were 3 rowers and 12 non-athletes. Participants’ average age was 40 years.
The study participants completed a clinical interview designed to establish their level of exposure to repetitive head injuries. They also underwent a diagnostic procedure for traumatic encephalopathy syndrome (a clinical condition associated with substantial exposure to repeated head impacts), a cognitive impairment assessment (the MoCA screening), and an assessment of depression symptoms (using the Beck Depression Inventory). Additionally, they underwent magnetic resonance imaging of their brains and provided blood samples.
Although all participating athletes had stopped their regular participation in contact sports for more than a year, results showed that 17 participants had extensive blood-brain barrier disruption. These individuals tended to show worse cognitive decline compared to participants with less extensive blood-brain barrier disruption. In retired athletes, a higher proportion of circulating monocytes, which is an indicator of a greater systemic inflammatory burden, was associated with stronger cognitive decline.
The study authors also found changes in immune-related pathways, particularly the complement system. The complement system is a vital part of the immune system. It consists of over 30 blood proteins that rapidly “complement” the ability of antibodies and white blood cells to clear pathogens, trigger inflammation, and destroy foreign cell membranes. These changes to the complement system may have contributed to the damage found around blood vessels in the brains of the study participants.
Overall, the findings suggest that repetitive head trauma may lead to long-lasting blood-brain barrier impairment and persistent inflammation, both of which may be involved in later cognitive problems and contribute to accelerated cognitive decline.
The study contributes to the scientific understanding of the health consequences of practicing combat and collision sports. However, it should be noted that the observational design of the study does not allow any definitive causal inferences to be derived from the results.
The paper, “Blood-brain barrier disruption, traumatic encephalopathy, and cognitive decline in retired athletes,” was authored by Chris Greene, Declan Brennan, Sheida Mirloo, Ruairi Connolly, Jeffrey O’Callaghan, Avril Reddy, Jeff Henderson, Gergő Porkoláb, Adam McGlinchey, Nicole Hanley, Siobhan Hutchinson, James F. M. Meaney, Michael Farrell, Sarah L. Doyle, Alon Friedman, Colin P. Doherty, and Matthew Campbell.