A study that followed more than 14,000 adults over 25 years found that just one head injury that leads to loss of consciousness could raise someone’s chances of developing dementia later in life — a risk that continues to grow as the number of injuries increase.
The findings also show stronger associations between head injuries and dementia risk for women compared to men and for white people compared to Black individuals, according to the study published Tuesday in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.
Although the study results are in line with others that have linked moderate and severe traumatic brain injury to a greater risk of developing dementia years later, the researchers say more work is needed to fully understand the observed sex and race differences.
“Head injury is a significant risk factor for dementia, but it’s one that can be prevented. Our findings show that the number of head injuries matter,” Dr. Andrea Schneider, the study lead investigator and an assistant professor of Neurology at the Perelman School of Medicine at the University of Pennsylvania, said in a statement. “The dose-dependence of this association suggests that prevention of head injury could mitigate some risk of dementia later in life. While head injury is not the only risk factor for dementia, it is one risk factor for dementia that is modifiable by behavior changes such as wearing helmets and seat belts.”
Dr. Schneider, together with colleagues from other institutions including Johns Hopkins Bloomberg School of Public Health, analyzed data on 14,376 adults in the U.S. who were a part of the Atherosclerosis Risk in Communities Study.
The participants were followed for a median of 25 years with up to six in-person visits and semi-annual phone follow-ups. Information on head injuries in which loss of consciousness occurred or in which medical attention was sought was either provided by the participants or collected from hospital records.
People with a history of one head injury were associated with a 1.25 times greater risk of dementia compared to those with no reported head injuries, the study found. A history of two or more prior head injuries was associated with more than double the risk of dementia. Overall, the researchers found that nearly 10% of the study participants who developed dementia had at least one prior head injury.
There were also stronger associations between head injuries and dementia risk among women (1.69 times greater risk) compared to men (1.15 times), and among white people (1.55 times) compared to Black people (1.22 times).
“Although there’s no known strategy to reduce the possible long-term risk of dementia once you’ve experienced a moderate or severe traumatic brain injury, or repeated mild traumatic brain injuries, it’s important to understand that not everyone who experiences a head injury in one of these categories develops dementia,” the Alzheimer’s Association says.
About 2.87 million traumatic brain injury-related emergency department visits, hospitalizations and deaths occurred in 2014, the latest year for which data is available, according to the Centers for Disease Control and Prevention.
Ongoing research on the connections between head injuries and dementia risks suggests that the injuries lead to increased levels of a specific protein that’s most associated with Alzheimer’s disease, the Alzheimer’s Association said.
A study in Sweden showed that the risk of dementia was highest the first year after a head injury, making those who experienced the injury four to six times as likely to develop dementia than those without an injury. It also revealed that a concussion or other traumatic brain injury can raise dementia risks 30 years later.
While mild injuries, or concussions, typically don’t cause loss of consciousness that exceeds 30 minutes, all forms of head injury can lead to difficulty learning and remembering new information, organizing thoughts or making sound judgments, the Alzheimer’s Association says. And those who experience a more severe injury could develop similar disabling symptoms years after the injury occurred.