WEDNESDAY, July 5, 2017 (HealthDay News) -- A severe head injury, especially during middle age, could dramatically boost the risk for developing dementia later in life, new research from Finland suggests.
The investigation tracked dementia risk among people who had suffered a traumatic brain injury [TBI] at 65 or younger. Ultimately, the researchers determined that not only did the risk go up for those who had a TBI, but the worse the initial head injury, the greater the risk of dementia.
"The study showed that 3.5 percent of persons with moderate-to-severe TBI [were] diagnosed with a neurodegenerative disease [such as dementia] later in life," said study lead author Dr. Rahul Raj. He's an associate professor of experimental neurosurgery at Helsinki University Hospital.
"This is substantially higher compared to age-matched peers with no history of brain injury," he noted.
By comparison, "only 1.6 percent of persons with mild TBI were diagnosed with a neurodegenerative disease," Raj added, placing moderate-to-severe TBI patients at a 90 percent greater risk for dementia than mild TBI patients.
The study authors pointed out that this research could only show an association; it could not prove a direct cause-and-effect link between traumatic brain injury and dementia.
In addition, a traumatic brain injury was only linked to a higher risk for developing dementia, not to a higher risk for other neurological conditions, such as Parkinson's or ALS (Lou Gehrig's disease).
The American Association of Neurological Surgeons (AANS) says that about 1.7 million Americans experience some form of traumatic brain injury each year, often resulting from a fall, a car accident or a firearm accident.
Among moderate-to-severe traumatic brain injury patients, roughly one in three ends up succumbing to their injury, Raj noted. One in two survivors end up struggling with lifelong disabilities. The AANS pegs the number of Americans living with a TBI-induced disability at more than 5 million.
The new study included more than 40,000 Finnish adults between 18 and 65 who had been hospitalized with mild, moderate or severe traumatic brain injuries. The injuries occurred between 1987 and 2014. The researchers followed the study participants for about 11 years.
The roughly 20,000 mild TBI patients were hospitalized for less than a day. None had experienced a traumatic brain lesion such as brain bruising, swelling, bleeding or a blood clot.
More than 20,000 moderate-to-severe traumatic brain injury patients had been hospitalized for a minimum of three days. All had been diagnosed with some form of serious brain lesion.
There was no significant difference between the two groups in terms of age, educational background or income.
Though above-average dementia risk was seen among all TBI patients, the moderate-to-severe group faced a substantially higher risk than the mild group.
The largest jump in risk was seen among those who had a traumatic brain injury between ages 41 and 50. Their odds of dementia were nearly triple those of someone with a mild injury.
For those who had a TBI between ages 51 and 60, the odds of dementia were doubled, the study showed.
More people in the moderate-to-severe group also ended up with dementia before the age of 65, compared to those in the mild group (40 percent versus 26 percent, respectively).
For TBI survivors, Raj said that "even after [a] seemingly [full] recovery there is an underlying elevated risk for dementia that probably won't ever go away.
"Thus, until we have a specific treatment for this, it is extremely important to minimize other risk factors for dementia, such as high blood pressure, high levels of cholesterol, diabetes, tobacco smoking and alcohol consumption," he noted.
Dr. Anton Porsteinsson is a professor of psychiatry and director of the Alzheimer's Disease Care, Research and Education Program at the University of Rochester School of Medicine in Rochester, N.Y. He said the findings suggest the effects of a traumatic brain injury can be "long-lasting or even permanent."
Why? Porsteinsson said a head injury likely triggers a loss of "brain reserve," while spurring on problematic shifts in overall brain chemistry.
"That the risk is highest in middle age is not surprising," he added, "as the brain has less ability to recover from injury at that time. And this is also the time period where the processes that may ultimately even decades later result in Alzheimer's disease tend to start."
The upshot, said Porsteinsson, is that "taking steps to minimize the risk of TBI is quite relevant" among the middle-aged, "no less so than in young athletes."
The study was published in the July 5 issue of PLOS Medicine.
There's more on traumatic brain injury at American Association of Neurological Surgeons.