There has long been a body of anecdotal evidence associating traumatic brain injury (TBI) and dementia, but the connection has remained largely unclear. Now, a team of researchers from Umea University in Sweden says they’ve found the strongest evidence yet showing that TBI can directly increase the risk for dementia in older adults.
According to the findings of a large study following millions of Swedish adults over the age of 50 for decades, the risk for dementia rises four- to six-fold in the first year after TBI.
According to the report published in PLOS ONE, the risk scaled with the severity of the brain injury, with those who experienced moderate, severe, or repeated TBIs facing the greatest risk. However, the overall odds of developing a dementia diagnosis after TBI decreased over time. These odds were still significantly higher than those without a history of TBI, though.
“Hopefully the potential impact of head injuries with respect to long-term outcomes will be a little more in the spotlight as a result of the study,” co-author Peter Nordstrom of the department of community medicine and rehabilitation at Umea University told Reuters Health by email.
While traumatic brain injury has recently been highlighted as a risk for athletes like football or hockey players, older adults actually face the highest risk statistically for TBI. Most of these brain injuries are the results of falls or other household accidents.
In the study, the researchers found that older adults with a recent history of TBI faced an 80% higher risk of being diagnosed with dementia during the 15-year follow-up period.
“I think this study is one of the strongest pieces of evidence to date that this relationship exists,” Patrick Frost Bellgowan told Reuters in a telephone interview. Bellgown is from the U.S. National Institute of Neurological Disorders and Stroke in Bethesda, Maryland, and wasn’t involved in the research. “The study’s strength is its size and quality of the data.”
However, Bellgowan notes the study is unclear when it comes to younger individuals.
“It is not going to inform us about concussion in young people and subsequent neurodegeneration,” Frost Bellgowan noted. “The study has hints of that, but the data is very sparse. We’ll have to wait decades to find out.”
For the study, Nordstron and a colleague reviewed the medical records of 3,329,360 Swedish adults over the age of 50 for any diagnoses of dementia or history of TBI.
Between the period of 2005 to 2012, they identified 164,334 people had been diagnosed and treated for TBI who had no prior diagnoses of dementia. They also found 136,233 people diagnosed with an unspecified form of dementia.
The two groups were both matched with control groups of similar but healthy individuals. A third group was also included, consisting of 46.970 sibling pairs, one of whom had a history of TBI.
Overall, the researchers found that 6.3 percent of those with a history of TBI and 3.6 percent of the rest of the study participants were diagnosed with dementia. In both groups, those with dementia were also likely to exhibit other risk factors for dementia such as age, alcohol use, early retirement, and depression.
The strongest association between dementia and TBI was in those diagnosed with dementia before the age of 65.
The results were also consistent in the group of sibling pairs, with no significant differences among genders.
In the first year after a “mild” concussion, individuals saw 3.52 times higher risk for developing dementia compared to those without TBI. While this risk subsequently declined, it remained 25 percent higher than the average person up to three decades later. This was especially true for cases involving vascular dementia.
While the findings contribute significant evidence tying dementia with a late-in-life concussion, the study authors note the findings are limited because they are based strictly on observation.
“There seems to be a relationship between TBI and dementia, but it will be tough to personalize it,” Frost Bellgowan said.