People with even a single concussion are more likely to develop dementia than people with no history of brain injuries, according to a University of Washington study published Tuesday in the British medical journal The Lancet.
The study is based on analyzing 36 years of medical records for nearly 2.8 million people in Denmark over age 50, and looking at their histories of brain injuries, dementia and other medical conditions.
Researchers, led by Jesse Fann, a professor of psychiatry and behavioral sciences at UW School of Medicine, found people with any traumatic brain injury were 1.5 times more likely than their noninjured peers to develop dementia, when controlling for demographic factors like age and gender.
“It certainly adds to the evidence that TBI is associated with negative not just short-term, but long-term, outcomes,” Fann said.
Even when controlling for other medical and psychiatric conditions associated with dementia, such as depression and hypertension, people with TBI were 1.24 times more likely to develop dementia than people without a brain injury.
Dementia remained relatively rare: only 4.7 percent of study participants developed dementia at all, a total of 126,734 people.
But the risk increased significantly for people with multiple brain injuries, and for people who were in their 20s at the time of their first brain injury.
A single, mild brain injury increased future dementia risk by 17 percent, Fann said. The risk increase jumps to 60 percent if that injury was in your 20s.
The data only includes injuries where patients sought hospital or emergency room treatment for a head injury, not injuries where people either did not seek care or went to a doctor’s office.
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.
Fann said his team’s research is able to provide better evidence of a link because of the large sample size, though the study is limited because it draws on patients from a single country that’s relatively ethnically homogenous.
The study also compared people with traumatic brain injuries to people with other types of traumatic injuries, like broken bones other than the skull or spine. Even compared to that group, the TBI group had higher risk for dementia.
Fann said future research that tries to narrow down why some people with brain injuries get dementia while other don’t is important.
People should also be aware of other risk factors for dementia, including excessive alcohol use, smoking, diabetes and hypertension.