Individuals who have experienced brain injuries have a higher risk of dementia later in life, research based on a study of nearly 3 million people in Denmark suggests.
Researchers identified people who’d experienced a traumatic brain injury (TBI) and those who hadn’t, and followed them up for an average of 10 years to see if they were subsequently diagnosed with dementia. A TBI is a head injury that causes damage to the brain. The damage can range from mild to life threatening.
Overall, researchers found brain injury is associated with a 24% increased risk of dementia.
The most important thing to realise, though, is that the absolute risks of developing dementia are still fairly small: 4.5% of people with no history of a TBI developed dementia, compared with 5.1% who had a traumatic brain injury.
While the association with TBIs and increased risk of dementia was found to be robust, only 1 in 20 of the full cohort of nearly 3 million experienced a TBI. Of these, only 1 in 20 of them (6,724) developed dementia.
This means rates of both were quite rare.
The researchers raise an interesting point that thanks to advances in trauma medicine, more people are now surviving serious TBIs. As such, there may be a need for more research and emphasis into cognitive rehabilitation approaches, as this may help reduce the risk of long-term complications.
The study was carried out by researchers from the University of Washington, Aarhus University Hospital, and Copenhagen University Hospital.
This was a population-based cohort study in Denmark which aimed to see whether a TBI is associated with a long-term risk of developing dementia.
Various previous studies have found a link between TBI and the development of dementia. But common pitfalls of these studies included an insufficient sample size and length of follow-up, a lack of accurate data collection, and the possibility of recall bias (people either forgetting they’d had a head injury or being more likely to recall one if they had cognitive problems they thought could be related).
The Research Methodology
The study used the Danish Civil Registration System to identify a population-based cohort of all Danish-born individuals who were living in the country in 1995 and who were aged 50 years or older from 1999 through follow-up to 2013.
Information on TBIs was collected from the Danish National Patient Register (NPR), which covers all hospital admissions, diagnoses and treatments.
Researchers identified all emergency department attendances and admissions from 1977 to 2013 where TBI was the main presenting cause. TBI was categorised as mild or severe based on the American Congress of Rehabilitation Medicine criteria.
Data on dementia diagnoses was obtained from the NPR, along with the Danish Psychiatric Central Register and the National Prescription Registry.
The researchers stated about two-thirds of people with dementia in Denmark are diagnosed in secondary care, and so are recorded in these registries.
Information on dementia diagnoses or receipt of dementia medications that occurred after 1999 was also collected.
The researchers analysed the risk of dementia among those who experienced a TBI and those who didn’t, and compared the results.
Fully adjusted models took account of possible confounding factors of age, gender, cardiovascular diseases, neurological conditions like Parkinson’s, and mental health conditions such as depression or bipolar disorder.
They also compared people who’d had a TBI with those who had experienced traumatic injury not involving the head or spine.
The study analysed a total population of 2.8 million people with an average of 10 years follow-up per person.
Of this cohort, 5% (132,093 people) had a diagnosis of TBI, the vast majority of which were mild injuries.
Characteristics of mild TBI include altered consciousness at the time of injury, development of some nerve-related problems, and some loss of memory at the time, but a loss of consciousness of less than 30 minutes and amnesia lasting less than 24 hours.
Only about 10% of TBIs were severe, and 5% involved skull fractures.
Out of the full cohort, 4.5% developed dementia (126,734 people) and 5.3% of these people (6,724) had experienced one or more TBIs. The average age at diagnosis was 81 years.
With full adjustment for confounders, any type of TBI was associated with a 24% increased risk of dementia when compared with people who hadn’t had a TBI (hazard ratio [HR] 1.24, 95% confidence interval [CI] 1.21 to 1.27).
The risk figure was very slightly higher for men than women (HR 1.30 versus 1.19). The risk was also slightly higher for severe TBI than mild TBI (HR 1.35 versus 1.17, both compared against no TBI).
Risk appeared to increase with the number of TBIs a person had, from HR 1.22 for 1 injury, 1.33 for 2 or 3, rising to HR of 2.83 for 5 or more.
TBI was also associated with a higher risk of dementia when compared with other traumatic injuries not involving the brain or spine (HR 1.29, 95% CI 1.26 to 1.33).
The researchers concluded that:
“TBI was associated with an increased risk of dementia both compared with people without a history of TBI and with people with non-TBI trauma. Greater efforts to prevent TBI and identify strategies to ameliorate the risk and impact of subsequent dementia are needed."
The study suggests TBI may be associated with an increased risk of dementia.
But it’s important to highlight that the absolute size of this risk increase is very small.
The study does has some limitations.
It looked at many potential confounders, but being an observational study there’s always a possibility some may have been missed.
The cohort was based in Denmark. Though any links between TBI and dementia may be expected to be consistent across populations, different health, lifestyle and environmental risk factors may mean that the results of this study aren’t directly applicable in other countries. For example, contact sports are less popular in Denmark.
There’s also the small possibility that mild cases of head injury or cognitive impairment not meeting medical attention have been missed.
Overall, this valuable study furthers our understanding about the size of any possible risk of dementia inferred from a head injury.
When it comes to a brain injury, prevention is very much better than any cure.
Ways to reduce the risk for you and your family include: ensuring your home (or those of elderly relatives) are free of trip hazards that could cause a fall, such as loose carpets or unnecessary items on the floor, childproofing your home – for example, by ensuring young children can’t reach windows or balconies, and using the right safety equipment for work, sport and DIY activities.
Fann, Jesse R et al. Long-term risk of dementia among people with traumatic brain injury in Denmark: a population-based observational cohort study The Lancet Psychiatry DOI: https://doi.org/10.1016/S2215-0366(18)30065-8
Image: Daria Kirpach, Wellcome Images