"People who have suffered traumatic brain injury (...) are at an increased risk of developing dementia, even decades after the injury", explains study leader Jesse Fann of the University of Washington School of Medicine in Seattle.
New research in the journal Lancet Psychiatry offers more evidence on the link between traumatic brain injuries and dementia for older adults. The highest risk of dementia was seen in the first six months after TBI (hazard ratio, 4.06), and the risk also increased with an increasing number of TBI events (hazard ratios, 1.22 to 2.83 for one TBI to five or more TBIs). But the risk increased significantly for people with multiple brain injuries, and for people who were in their 20s at the time for their first brain injury.
According to United Nations data, around 50 million people around the world suffer from dementia, such as Alzheimer's disease.
Prior studies of traumatic brain injury and dementia have struggled to establish a link because of low sample sizes or study intervals that were too short to observe dementia development.
Researchers obtained their TBI data from the Danish National Patient Register, while information on dementia involved a combination of data from the National Patient Register, the Danish Psychiatric Central Register and the Danish National Prescription Registry.
The study included 36 years of follow-up, as well as access to a uniform healthcare system that tracks the number and severity of TBIs.
Leading causes include falls, motor vehicle accidents, and assaults.
The scientists involved in the brain injury and dementia research identified every diagnosis of TBI from the health records of a Danish population of 2.8 million people between 1977 and 2013.
The idea that blows to the head suffered by boxers and footballers may increase the risk of dementia is a hotly debated issue.
The association between TBI and dementia held true even when comparing people with a history of TBI to those with non-TBI fractures not involving the skull or spine.
Overall, the risk of dementia was slightly higher in men who had sustained a TBI compared to women.
A single TBI increased the risk by more than a third. "Our findings suggest that improved traumatic brain injury prevention programmes may have an opportunity to reduce the burden of dementia worldwide".
Writing in a linked Comment, Professor Carol Brayne from the Cambridge Institute of Public Health, University of Cambridge, Cambridge, UK says, "Now we need to tease out what is happening in terms of TBI, wider spectrum exposures, and how these occur across different ages, by gender, and also by community within societies".