Traumatic brain injury raises dementia risk, large study suggestsBMJ 2018; 361 doi: https://doi.org/10.1136/bmj.k1597 (Published 11 April 2018) Cite this as: BMJ 2018;361:k1597
People who have sustained a traumatic brain injury have a higher risk of developing dementia and Alzheimer’s disease, a nationwide population cohort study suggests.
Published in the Lancet Psychiatry,1 the study is one of the first to have a sufficient sample size and follow-up time to assess the effects of traumatic brain injury.
It includes data on 2 794 852 people living in Denmark on 1 January 1995 who were aged at least 50 at some point in the follow-up period (1999-2013). Registries were used to identify people who had sustained a traumatic brain injury from 1977 to 2013 and those who had had dementia diagnosed.
Over the 36 year study period 132 093 people (4.7%) had at least one traumatic brain injury, and 126 734 (4.5%) had dementia diagnosed during 1999-2013. Data analysis showed that people who had sustained at least one traumatic brain injury were 24% more likely to have dementia diagnosed than those without a history of traumatic brain injury (hazard ratio 1.24 (95% confidence interval 1.21 to 1.27)) and 16% more likely to have Alzheimer’s disease diagnosed (1.16 (1.12 to 1.22)).
The risks for dementia increased with the number of traumatic brain injuries experienced, rising from 1.22 (1.19 to 1.25) with one injury to 2.83 (2.14 to 3.75) with five or more. Severity of injury was also linked to a higher dementia risk, and even a single mild injury (concussion) was linked to a 17% higher risk.
Dementia risk was highest in the first six months after the traumatic brain injury (4.06 (3.79 to 4.34)) and then decreased with time. The younger the person was when sustaining the injury, the higher the hazard ratio for dementia when stratified over time. The researchers said that this may be because several other risk factors for dementia are common in older people.
They wrote, “From a public health perspective, traumatic brain injury prevention programmes have an opportunity to reduce the burden of dementia worldwide.”
Carol Brayne, from the Cambridge Institute of Public Health at the University of Cambridge School of Clinical Medicine, UK, said in a linked commentary,2 “Traumatic brain injuries have various origins, with road traffic injuries and military exposures being important. The probability of survival after traumatic brain injury has changed radically in high income countries.
“Traumatic brain injury is a sufficient enough concern for international consortia to be formed to attempt to support better care across the world, and head injury research now encompasses episodes without loss of consciousness.
“It will be many years before the outcomes of the mildest traumatic brain injuries studied in younger adults will be known, as it will be decades before the age groups in which this is of greatest interest to society and health services will reach the age of highest dementia risk.”