Repeated concussions are linked to worse brain function later in life, according to the largest study to date exploring the cognitive effects of concussion, or traumatic brain injury.
It will add further pressure on sporting bodies to better reconsider a willingness to allow repeated traumatic brain injury (TBI) among their athletes, and motor vehicle and workplace insurers who will further understand the life-long health care needs of people experiencing mild head trauma in accidents.
The report, in the Journal of Neurotrauma, found that people who reported experiencing three or more concussions in their lifetime had worse baseline cognitive function than those that had never experienced concussion.
Researchers from the University of New South Wales, and Oxford and Exeter in the UK, analysed the data of more than 15,000 participants and found that just one moderate-to-severe concussion was associated with worse concentration, ability to complete complex tasks and processing speed.
(Significant limitations of this study are described below).
People who reported three episodes of even mild concussions had significantly worse concentration and ability to complete complex tasks, and participants with four or more mild concussion episodes showed worse processing speed and working memory.
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“Our findings suggest concussions are associated in the long-term with a fixed chronic deficit that seems to increase with each additional TBI,” says Dr Matthew Lennon MD, a PhD candidate from the Centre for Healthy Brain Ageing (CHeBA) at UNSW Medicine & Health and lead author of the study.
“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,” adds Dr Vanessa Raymont, a psychiatrist and senior author of the study from the University of Oxford.
The team analysed data from 15,764 participants of the online PROTECT study – an ongoing, UK-based, long-term research project seeking to better understand how the brain ages and why people develop dementia.
It studied people between 50 and 90 years old, who were asked to report the frequency and severity of concussions throughout their lives using the Brain Injury Screening Questionnaire (BISQ).
Participants also completed annual online cognitive tests over four years to track changes in cognitive function over time. Those diagnosed with dementia at baseline were excluded from the study.
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“As our population ages, we urgently need new ways to empower people to live healthier lives in later life,” says Dr Helen Brooker, co-author and senior research fellow from the University of Exeter.
“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 concentration span and completion of complex tasks, which we found to be especially susceptible to long-term damage.”
The authors say that people with a history of concussions should be wary of the potential dangers of continuing activities that may place them at risk of further head trauma, like contact sports and dangerous work.
“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,” Raymont says.
Limitations of the study
Of all study participants, 6,227 (39.5 per cent) reported at least one concussion, and 510 (3.2 per cent) at least one moderate-severe concussion. 3711 (23.5%) had suffered at worst a non-TBI head strike and 5818 (32.9%) reported no head injuries at all.
On average, they reported suffering their last head injury 29 years prior to the study and their first head injury 39 years earlier.
“The retrospective design of the study, with elderly participants often recalling details of events over three decades in the past, may have affected the reporting of head injuries, even while using a well-validated screening tool,” Lennon says.
The researchers also acknowledge that some unmeasured variables known to affect cognitive scores, may have also influenced the study results.
“We were able to control for the critical confounding variables including age, sex, education, smoking and vascular risk, but unmeasured confounders such as socioeconomic status may explain some of the variation between groups,” concludes Lennon.