In one of the largest studies on the association, researchers found people who suffered traumatic brain injuries were more likely to develop dementia and Alzheimer's disease. A traumatic brain injury can occur when there is a bump, blow or jolt to the head.
In one of the largest studies on the subject, researchers studied 2.8 million patient records. They found people with a history of brain injury had a 24 percent higher risk of dementia than those who did not.
The Centers for Disease Control and Prevention defines traumatic brain injury as "a disruption in the normal function of the brain that can be caused by a bump, blow or jolt to the head, or penetrating head injury."
Approximately 50 million people worldwide experience such injuries per year, a press release from the University of Washington School of Medicine reported. About 47 million people worldwide suffer from dementia.
According to the study, a single traumatic brain injury defined as "severe" increased the risk of developing dementia by 35 percent. A single incident of a "mild" case or concussion increased the risk by 17 percent.
The number of brain injuries greatly increases the chances of developing dementia or Alzheimer's disease. People who suffered two or more traumatic brain injuries had a 33 percent increased chance. People who had suffered four or more had a 61 percent increased chance, and people who suffered five or more had a 183 percent increased chance.
"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 the press release. Fann is a professor of psychiatry and behavioral sciences at the university.
"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."
When a person suffers a traumatic brain injury also affects the likelihood of developing dementia. If someone suffers a brain injury in their 20s, they are 60 percent more likely to develop dementia or Alzheimer's disease in their 50s.
This is concerning because traumatic brain injuries are more common in younger people.
While not every person who suffers a single traumatic brain injury or concussion will eventually develop dementia, the findings may prompt those with histories of such injuries to alter their lifestyles and take control of other risk factors for dementia, including limiting alcohol and tobacco use, increasing exercise, preventing obesity and treating diabetes.