A traumatic brain injury that results in a loss of consciousness for more than five minutes increases the risk of being diagnosed with mild cognitive impairment (MCI), report researchers at the University of Texas Southwestern Medical Center.

In addition, those who suffered injuries showed signs of MCI more than two years earlier than those with no traumatic brain injury (TBI).

Although there is no record for those who sustain TBIs, but don't visit an emergency room or hospital, the Centers for Disease Control and Prevention estimates that TBIs were responsible for 2.5 million visits to emergency rooms, hospitalizations, and deaths in 2010.

The Texas study analyzed cases of 3,187 people diagnosed with mild cognitive impairment versus a group of 3,244 people with normal cognition.

Several studies have implicated traumatic brain injury as a risk factor for developing neurodegenerative disorders, such as Alzheimer's disease, later in life, but this study was the first to show a link between TBI and MCI.

"This is one of the first studies to demonstrate later-life risks of mild cognitive impairment in relation to a remote history of traumatic brain injury in a large population sample," said senior author Dr. C. Munro Cullum.

The researchers found TBI patients who had lost consciousness were 1.2 to 1.3 times more likely to be diagnosed with MCI than those who had not suffered brain injuries. They also found a link between elevated risk and a history of depression.

"We cannot yet determine who is at greatest risk for later-life cognitive decline following TBI, but these results suggest that a relationship exists for some people," Cullum said. "Our ultimate goal is to identify various risk factors that may play a role."

The study was published in the Journal of Alzheimer’s Disease.