In the United States, each year an estimated 1.7 million individuals experience a traumatic brain injury, or TBI, according to the Centers for Disease Control and Prevention.
A TBI may be a closed head injury — in which the head strikes an object — or a penetrating head injury — in which the object breaks through the skull and can come in contact with the brain tissue.
A TBI can range from mild to severe. The Centers for Disease Control and Prevention noted that 75 percent of annual TBI cases are either concussions or another type of mild TBI.
Concussions are the most common form of TBI and are also the most minor, according to the National Institute of Neurological Disorders and Stroke.
One area of concern with TBI is the risk of developing dementia later in life. Dementia symptoms have been noted in individuals who have careers where they have sustained head injuries.
For example, career boxers may be vulnerable to dementia pugilistica, or chronic traumatic encephalopathy. The National Institute of Neurological Disorders and Stroke said that boxers can begin displaying symptoms of dementia 6 to 40 years after starting their career.
So what does the new research say about the risk of developing dementia in individuals who have had a TBI?
One recent study followed 4,225 individuals ages 65 and older (the average age was 75) who did not have dementia at time of enrollment. Participants were in the study for up 16 years (the mean was 7.4 years) and were seen every two years.
Researchers collected information on participants’ TBI history. About 14 percent of the participants had a history of a TBI with a loss of consciousness when they enrolled in the study.
The researchers found that that having a history of a TBI with a loss of consciousness did not increase the risk of developing Alzheimer’s disease or another type of dementia.
However, they found that if an individual had her first head injury before the age of 25, her risk for having another TBI more than doubled. If her first TBI occurred after the age of 55, her risk of having another one nearly quadrupled.