A major new study has confirmed that multiple concussions are associated with cognitive defects in later life. The findings have important implications for counselling and cognitive rehabilitation after head injury.
Moderate-to-severe traumatic brain injury (TBI) was already known to cause later cognitive impairment, with the risk of dementia elevated 1.5- to 3-fold. However, which cognitive domains are most affected remained contested, the effects of mild TBI and the time course of the deficits was unclear, and the impact of repeated TBI remained moot.
Researchers led by the Universities of Oxford and Exeter used data from a subset of more than 15,764 people enrolled in the ongoing online PROTECT-TBI Cohort Study, the largest of its kind assessing risk factors for cognitive decline, to analyse the longer-term cognitive effects of TBI severity and number. Participants, all aged between 50 and 90 and based in the UK, share detailed lifestyle information and complete a suite of computerised cognitive tests every year, for up to 25 years.
For the new study, they were asked retrospectively to recalled lifetime TBI severity and number using the Brain Injury Screening Questionnaire, and the researchers correlated this with cognitive test results over 4 years, covering working memory, episodic memory, attention, processing speed, and executive function.
Over a Third of Participants Reported at Least One Head Injury
Overall, 5725 (36.3%) participants reported at least one mild TBI and 510 (3.2%) at least one moderate-severe TBI, whereas 3711 (23.5%) had suffered at worst a non-TBI head strike and 5818 (32.9%) reported no head injuries. The last reported head injury had occurred an average of 29.6 (standard deviation 20.0) years prior to the study.
Results, published in the Journal of Neurotrauma, showed that having just one moderate-to-severe concussion could have a long-term impact on brain function, including significantly impaired memory, attention, completion of complex tasks, and processing speed capacity, compared with participants without a history of head injury. Even those who had suffered a single mild TBI also demonstrated significantly poorer average attention scores at baseline compared with the no head injury group.
People who reported three or more lifetime concussions, even with mild TBI, had significantly worse cognitive function, with poorer baseline executive function and attention scores particularly affected, and this got successively worse with each additional reported concussion. Those who had four or more mild concussion episodes also showed worsened attention, processing speed and working memory.
Traumatic Brain Injury Associated With Cognitive Deficits
The researchers said: "TBI is associated with fixed, dose-, and severity- dependent cognitive deficits. The most sensitive cognitive domains are attention and executive function, with approximately double the effect compared with processing speed and working memory." They concluded: "Significant long-term cognitive deficits were associated with three or more lifetime mild TBIs," and recommended that "post-TBI cognitive rehabilitation should be targeted appropriately to domain-specific effects".
People at Risk 'Should be Warned'
The team also pointed out that 1.4 million people (2% of the population) in the UK attend emergency departments each year with a head injury. It was the leading cause of death in people under age 40, and estimated to contribute between 3.4% and 15% of the total dementia burden. They said that the risks should be "a critical consideration when counseling individuals post-TBI about continuing high-risk activities", and recommended that people who have sustained concussions should be warned of the dangers of continuing high-risk sport or work.
Lead investigator Dr Vanessa Raymont, a senior clinical researcher at the University of Oxford, said: "We know that head injuries are a major risk factor for dementia, and this large-scale study gives the greatest detail to date on a stark finding - the more times you injure your brain in life, the worse your brain function could be as you age.
"Our research indicates that people who have experienced three or more even mild episodes of concussion should be counselled on whether to continue high-risk activities. We should also encourage organisations operating in areas where head impact is more likely to consider how they can protect their athletes or employees."
Study co-author Dr Helen Brooker, a senior research fellow at the University of Exeter, said: "As our population ages, we urgently need new ways to empower people to live healthier lives in later life. This paper highlights the importance of detailed long-term studies like PROTECT in better understanding head injuries and the impact to long term cognitive function, particularly as concussion has also been linked to dementia.
"We're learning that life events that might seem insignificant, like experiencing a mild concussion, can have an impact on the brain. Our findings indicate that cognitive rehabilitation should focus on key functions such as attention and completion of complex tasks, which we found to be susceptible to long-term damage."
Robust Guidelines Needed
Dr Susan Kohlhaas, director of research at Alzheimer's Research UK, commented: "Studies like this are so important in unravelling the long-term risks of traumatic brain injury, including their effect on dementia risk. These findings should send a clear message to policy makers and sporting bodies, who need to put robust guidelines in place that reduce risk of head injury as much as possible."
Asked by Medscape News UK to comment on the study, Headway, the Brain Injury Association, said: "Through our work, we know that traumatic brain injuries can be life-changing, with cognitive effects such as memory, attention and concentration problems particularly challenging due to their 'hidden' nature.
"This new research highlights how frequency and severity of brain injury can be linked to cognitive effects later in life, and this work on concussion is particularly pertinent given the current focus on concussion risk in the sporting world.
"The cognitive impact of concussions is one that must be taken seriously, this new body of evidence helps with that understanding and recognition as there are lifelong, and unfortunately often devastating consequences."
This study represents an independent research project partly funded by the National Institute for Health Research Biomedical Research Centre at South London and Maudsley NHS Foundation Trust and King's College London. This research was also supported by the NIHR Collaboration for Leadership in Applied Health Research and Care South West Peninsula.