In fact, those with TBIs were collectively 24 percent more likely to have dementia and 16 more likely to develop Alzheimer's disease. Those with a severe TBI were 35 percent more like to develop dementia, and those with a mild one were 17 percent more likely to get it.
The numbers were even higher for those with multiple injuries. People with three TBIs had a 33 percent higher higher risk, those with four had a 61 percent higher risk and those with five or more had a 183 percent higher risk.
"What surprised us was that even a single mild TBI was associated with a significantly higher risk of dementia," lead author Jesse Fann said in a statement. "And the relationship between the number of traumatic brain injuries and risk of dementia was very clear ... Similarly, a single severe brain injury seems to have twice the risk associated with dementia as a single mild traumatic brain injury."
Furthermore, those who had a brain injury in their 20s were 60 percent more likely to develop dementia in their 50s. And among men and women with TBI histories, men had a slightly higher rate of developing dementia
Despite their findings, the researchers noted that people who sustain one concussion or a severe TBI will not necessarily develop dementia. However, they believe their findings will help people with a history of TBIs avoid other potential risk factors, including alcohol and tobacco use, obesity and hypertension.
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The researchers now hope to continue their investigations to understand the groups at greater risk of dementia, particularly children involved in contact sports.
"If someone has a traumatic brain injury or concussion, they need to strictly follow the protocols to leave the game and get the proper assessment and treatment that is necessary," Fann said. "If they have a history of traumatic brain injury, they should do their best to prevent further traumatic brain injuries."