Alzheimer's disease has become an increasing burden in older patients, which is why research into its causes is a high priority. Now, a new study links concussion history and Alzheimer's, suggesting loss of consciousness could be associated with the build-up of plaques in the brain.
The researchers, including study author Michelle Mielke from the Mayo Clinic in Minnesota, published their findings in the journal Neurology.
In 2010 in the US alone, over 83,000 individuals died as a result of Alzheimer's disease, making it number six on the cause of death list, according to the Centers for Disease Control and Prevention (CDC).
The most common form of dementia, Alzheimer's interferes with memory, behavior and thinking ability. Though symptoms can develop slowly, they eventually get worse over time.
To conduct their research, the team performed brain scans on individuals over 70-years-old in Minnesota, 448 of whom did not show any signs of memory problems and 141 of whom had memory and thinking problems - referred to as mild cognitive impairment.
The participants were also asked about concussion history - specifically, whether they had ever had a brain injury that involved loss of consciousness or memory.
Amyloid plaque levels and head trauma
The latest research links concussion history with a build-up of amalyoid plaques, suggesting head injuries could be associated with the development of Alzheimer's disease.
In the group that did not display any memory or thinking problems, 17% reported experiencing a brain injury, while 18% of the group with memory/thinking difficulties reported having a concussion or trauma to the head.
The researchers note that whether or not the individuals had experienced head trauma, they did not find a difference in brain scan measures among the group without memory or thinking impairments.
However, in the group of individuals with memory and thinking problems, the investigators observed that those who had experienced head trauma had amyloid plaque levels that were on average 18% higher than those without a history of head trauma.
"Interestingly, in people with a history of concussion, a difference in the amount of brain plaques was found only in those with memory and thinking problems, not in those who were cognitively normal."
This is not the first study to make such a connection, however. Another recent study found a tentative molecular link between head injury and Alzheimer's.
That study, conducted by researchers at the University of Cambridge in the UK, suggested that small amounts of a protein called tau - which clumps abnormally in the brains of individuals who have died of Alzheimer's - escape from the inside of cells to the outside after being triggered by an event, such as a head injury.
Back to the latest study, Mielke says their "results add merit to the idea that concussion and Alzheimer's disease brain pathology may be related."
"However," she adds, "the fact that we did not find a relationship in those without memory and thinking problems suggests that any association between head trauma and amyloid is complex."