TBI may increase risk for dementia, Alzheimer’s disease

Results from a nationwide cohort study in Denmark of more than 2 million people aged 50 years and older showed that those who sustained a traumatic brain injury were more likely to develop all-cause dementia and Alzheimer’s disease than those with no history of injury.

Furthermore, this risk increased as the number of traumatic brain injuries (TBI) and the severity of injury increased, according to findings published in The Lancet Psychiatry .

“Dementia and TBI are major causes of disability worldwide, and their relationship to each other has been thrown into the spotlight in recent years among military veterans and participants of contact sports. There have been conflicting data published on the impact of TBI on risk of developing dementia,” Jesse R. Fann, MD, MPH, professor of psychiatry and behavioral sciences, University of Washington, Seattle, told Healio Psychiatry . “These conflicting findings are due in part to limitations in study samples and methodology. Our research group sought to address this important question by capitalizing on the advantages of the Danish national health registry.”

To investigate the relationship between TBI — including severity and number of injuries — and the following long-term risk for dementia, researchers conducted a nationwide population-based observational cohort study in Denmark of adults aged 50 years and older. Using data from Danish registries spanning 36 years, the investigators performed survival analysis to determine the long-term risk for dementia after TBI. They used three models that measured different time periods since the TBI, multiple TBIs, and sex; the first model was adjusted for sociodemographic factors, the second for medical and neurological comorbidities and the third for psychiatric comorbidities.

Out of nearly 2.8 million people included in the cohort, 132,093 (4.7%) sustained at least one TBI during the 36-year period, most of which were mild (85%), and 126,734 (4.5%) developed dementia during the 14-year follow-up. In the adjusted model, the risk for all-cause dementia in people with a history of TBI was higher (HR = 1.24; 95% CI, 1.21–1.27) than the risk for those without a history of TBI. The risk for Alzheimer’s disease was also higher among those who experienced a TBI (HR = 1.16; 95% CI, 1.12–1.22).

Fann and colleagues found that the risk for dementia was highest in the 6 months following TBI (HR = 4.06; 95% CI, 3.79–4.34). Furthermore, the risk for dementia increased with the number of events (HR = 1.22; 95% CI, 1.19–1.25 for one event and HR = 2.83; 95% CI, 2.14–3.75 for five or more), and with the severity of the TBI. In addition, when stratifying the risk for dementia by time since TBI, the researchers found that the risk for dementia was higher among people who were younger when they sustained the TBI.

“Although their risk is elevated, a person who sustains a TBI is not guaranteed to develop dementia later in life,” Fann told Healio Psychiatry .

“Importantly, a person who has sustained a TBI should do what they can to prevent further TBIs, as the risk of dementia increases with the number of TBIs, and we know that people with a history of TBI are at higher risk for subsequent TBIs,” he continued. “It also is important to address other known risk factors for dementia that are potentially modifiable, such as limiting alcohol and tobacco use, engaging in regular exercise, preventing obesity, and treating hypertension, diabetes and depression. Evidence-based cognitive rehabilitation strategies may also be helpful in minimizing the negative impact of TBI on cognitive functioning.”

These findings warrant further study of the way clinical research evaluates TBI exposures and outcomes, Carol Brayne , M D, Cambridge Institute of Public Health, University of Cambridge School of Clinical Medicine, U.K., wrote in a related comment.

“The long-term outcomes of TBI are challenging to understand, but given improvements in survival in more recent generations, because of transformation of care in the immediate stages following injury, there are changing considerations about such long-term outcomes,” she wrote. “It will be many years before the outcomes of the mildest TBIs 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.” – by Savannah Demko

Disclosures: The authors report no relevant financial disclosures. Brayne reports no relevant financial disclosures.