Veterans who have survived traumatic brain injuries are 60 percent more likely to develop Alzheimer’s disease and other forms of dementia later in life, a new study found. Those who developed dementia also tended to develop it about two years earlier than veterans who hadn’t had brain injuries, the study found.
The findings add to growing evidence that serious head injuries may contribute to brain problems like Alzheimer’s years down the road.
“These findings suggest that a history of traumatic brain injury contributes risk for dementia in later life in veterans,” said study author Deborah E. Barnes of the University of California, San Francisco and the San Francisco Veterans Affairs Medical Center.
The findings, published in Neurology, show only a correlation between brain injury and Alzheimer’s; they cannot prove a cause and effect relationship. But “if we assume that this relationship is causal,” said Dr. Barnes, “it seems likely that the same increased risk probably occurs with traumatic brain injury in the civilian population as well.”
The study involved 188,784 veterans aged 55 and older who were free of dementia at the study’s start. Their average age was 68. All had visited at a V.A. hospital when the study began, and again about nine years later. They were given tests to look for signs of dementia and assessed for other mental health and medical problems.
Of the veterans, 1,229 had suffered a traumatic brain injury, or TBI, during service. During the study’s nine-year follow-up period, 196, or 16 percent, developed Alzheimer’s or another form of dementia. In comparison, about 10 percent of those without a brain injury were given a dementia diagnosis.
The researchers controlled for factors like diabetes, high blood pressure, depression and alcohol abuse, all of which can increase dementia risk. They determined that veterans who had had brain injuries were 60 percent more likely to develop dementia than those without a brain injury.
Of course, many of the veterans who had had traumatic brain injuries never developed dementia. And some of those who had never had a serious brain injury developed dementia. But over all, veterans with TBI tended to develop dementia about two years earlier, around age 78, than those without a TBI.
The researchers also found that the risk of dementia was higher in veterans with TBI who also had depression, post-traumatic stress disorder or blood vessel disease than in those with either TBI or these other conditions alone. The study was supported by the U.S. Department of Defense and the National Institutes of Health.
Other research has shown that brain injury is linked to a variety of health problems, including an increased risk of seizures, memory and thinking problems and early death. It has long been known that boxers, for example, may suffer from cognitive problems later in life, and similar deficits have been documented in football players and other athletes. Genetics and other factors may predispose some people to memory problems after head trauma.
This study looked at head injuries in veterans in particular, including related risk factors like post-traumatic stress disorder and depression. The injuries were far more severe than the kinds of concussions seen on the playing field.
“The authors convincingly showed that mild trauma has a role in increasing the risk of dementia and sheds light on the more complex relationship between medical and psychiatric diseases with TBI in the development of the future risk of dementias,” wrote Dr. Rodolfo Savica of the University of Utah School of Medicine in an editorial accompanying the study. He cautioned that the relationship between head trauma and Alzheimer’s disease is complex and that more study is needed to determine how injuries might prime the brain for dementia onset. “Head trauma is just one piece of a big puzzle,” he said.
Alzheimer’s researchers have become concerned that brain injuries, possibly even mild to moderate concussions, can cause brain inflammation that then triggers the development of Alzheimer’s in those who may already be at increased risk of the disease.
Source: Deborah E. Barnes, PhD, MPH, Allison Kaup, PhD, Katharine A. Kirby, MA, et al: “Traumatic Brain Injury and Risk of Dementia in Older Veterans.” Rodolfo Savica, MD, MSC: “Head Trauma and Neurodegeneration in Veterans: An Additional Piece of the Puzzle.” Neurology Vol. 83, No. 1-8, 2014.