Results of a new study show that elderly people who both have mild cognitive impairment and a history of concussion involving momentary loss of consciousness have higher amounts of protein deposits which are associated with Alzheimer's disease.

The study, which was published online in the journal Neurology, involved 448 residents of Olmsted County in Minnesota who had no signs of memory problems and 141 residents with memory and thinking problems. The researchers asked the participants, who were all 70 years or older, whether they have ever experienced brain injury that involved any loss of consciousness or memory.

Brain scans done on all the participants showed that those who had both concussion history and cognitive impairment, had levels of amyloid plaques that were 18 percent higher than those with cognitive impairment but no head trauma history. Among participants with mild cognitive impairment, those who have concussion histories were also five times more at risk of elevated plaque levels than those without a history of concussion.

Amyloids are a kind of fibrous proteins whose buildup in the brain has been associated with neurological disorders such as Alzheimer's disease. According to the Alzheimer's Association, most people develop this with age but those who develop Alzheimer's generally get many more.

The researchers suggested that the higher amyloid levels in cognitively impaired participants could be a response to a higher level of damage to the myelin coating of the axons of neurons, the brain's white matter.

Previous studies looking at whether head trauma is a risk factor for Alzheimer's have conflicting results, but study researcher Michelle Mielke, an associate professor of epidemiology and neurology at Mayo Clinic Rochester said that she has found only a link or association and not a cause-and-effect relationship.

''What we think it suggests is, head trauma is associated with Alzheimer's-type dementia -- it's a risk factor," she said. "But it doesn't mean someone with head trauma is [automatically] going to develop Alzheimer's."

Dr. Joseph Masdeu director of the Nantz National Alzheimer Center at Houston Methodist Hospital says genetics play the biggest risk factor for Alzheimer's. "If an immediate family member has it, the risk goes up four-fold," he said.