A new study finds that even a mild concussion that occurs years ago can have long-term effects on brain function and behavior in healthy individuals. The study adds to the growing understanding of traumatic brain injury and is relevant to the evolving legal landscape around brain injuries in sports.
A concussion is a mild form of traumatic brain injury (TBI) that can occur from events such as a fall, car accident, contact sports or assault. The resulting impairment in brain function is generally thought to be temporary. However, there is increasing evidence that TBI is a risk factor for dementia, which has led to research led by the University of Cambridge in England to investigate how the brain behaves in the long term after even a mild TBI.
They recruited 617 healthy middle-aged British adults aged 40 to 59 as part of the Prevent Dementia study. Participants underwent MRI scans and neuropsychological testing to assess brain structure and function, and their history of TBI was assessed using the Brain Injury Screening Questionnaire (BISQ). TBI was defined as experiencing at least one blow to the head that resulted in loss of consciousness. Mild TBI was defined as loss of consciousness for less than 30 minutes. The risk of cardiovascular disease was also assessed.
Of the 617 participants, 36.1% reported at least one TBI with loss of consciousness. Of these, 56.1% reported a single TBI event, 27.4% reported two TBI events, and 16.6% reported more than two TBI events. Injury severity was determined for 76.2% of the 223 participants with a history of TBI, with 94.1% reporting mild TBI and 5.9% reporting moderate-severe events with loss of consciousness lasting 30 minutes or longer.
Cerebral microbleeds—small, chronic brain hemorrhages—were detected in approximately one-sixth (17.7%) of participants. Compared with those without TBI, the number of microbleeds was greater in participants with a previous TBI, including those with mild TBI. A greater number of TBI events were associated with worse sleep, gait disturbances, more symptoms of depression, and memory deficits, but not attention deficits. The mild TBI group had worse sleep, depression, and gait, but no cognitive impact.
The researchers examined the relative contribution of TBI and cardiovascular risk factors (e.g., high blood pressure, diabetes) to these clinical deficits and found that TBI was the most significant contributor to depression and sleep (but not to cognition or gait) and outweighed the contribution of cardiovascular risk factors. Although TBI dominated cardiovascular risk factors in contributing to memory deficits, the major predominant factors were sex and age.
“These data demonstrate that in otherwise healthy middle-aged adults, a history of remote TBI is associated with detectable changes in vascular brain imaging and clinical features,” the researchers wrote. “Overall, our findings have important implications for future research directions as well as informing clinical practice and policy making at the community level.”
To inform clinical practice, evaluating for TBI in situations where a person is known to have suffered a brain injury could help identify which patients are at higher risk and get their symptoms treated sooner, the researchers say.
The issue of TBI in sports has become a significant concern in recent years as more and more evidence emerges about the short-, medium-, and long-term consequences of the damage caused by such injuries. Most examples come from contact sports such as boxing and martial arts, soccer, hockey, and football, and the legal landscape around this issue has changed as a result.
Brain injury lawsuits are increasingly common in sports, with athletes holding organizations and individuals accountable for injuries sustained while playing. In 2015, the NFL in the US reached a class-action settlement promising to pay compensation to former players diagnosed with concussion-related dementia or other brain diseases, without admitting any wrongdoing. Washington PostSince the NFL Concussion Settlement was finalized, nearly $1.2 billion has been paid to more than 1,600 former players and their families, far more than experts had estimated during the settlement negotiations. As of August 19, there were 20,572 registered settlement class members.
In the UK, a class action is currently ongoing across various rugby codes targeting the sport’s three governing bodies. In the case, 295 former players, both amateur and professional, male and female, aged between 22 and 80, claim that World Rugby, England’s Rugby Football Union and the Welsh Rugby Union failed to take reasonable measures to protect the health and safety of players.
The topic is also a hot topic in Australia. In April of this year, Australian Football League (AFL) player Nathan Murphy announced his retirement from the sport at the age of 24. Murphy retired on the advice of a medical panel after suffering the tenth concussion of his career. However, Murphy is neither the first nor the youngest player to retire early from the AFL due to a head injury. In 2016, Justin Clarke, then 22, retired from the game after suffering weeks of memory loss as a result of a concussion. In 2023, two class actions were filed in the Supreme Court of Victoria against the AFL alleging concussions during training and/or matches.
Then there’s the issue of chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease associated with repeated head trauma. It’s controversial because no definitive causal link has been established between CTE and contact sports, but studies strongly suggest it. One such study of former NFL players with mood, behavioral, or cognitive symptoms found that 99 percent showed signs of CTE. The problem is that the condition can only be diagnosed at autopsy.
These often complex and emotional legal cases have ushered in a new era of safety in contact sports, but the question that all of them raise is this: Will sports organizations adapt safety rules or change concussion protocols to better manage risk and prevent future lawsuits?
A cultural change is also needed. While receiving submissions for his recently published report, Concussion and repetitive head trauma in contact sportsThe Senate Community Affairs Standing Committee of the Australian Parliament heard evidence of under-reporting of concussions from athletes who fear they will be told not to play or will let their team down. The 'win at all costs' attitude of athletes prioritising long-term wellbeing also needs to change.
The research, led by Cambridge University, was published in the journal JAMA Network Open.