Previous studies had found that 15% to 20% of military service members returning from Iraq and Afghanistan have developed post-traumatic stress disorder, but that research has not fully explored the potential risk the disorder holds for dementia, said Yaffe, chief of geriatric psychiatry at the San Francisco Veterans Affairs Medical Center and a professor at UC San Francisco.
In the study presented at the International Conference on Alzheimer's Disease in Vienna, Yaffe and her colleagues followed about 181,000 veterans age 55 and older in the VA's National Patient Care Database. About 30% of these veterans had post-traumatic stress disorder.
The researchers found that about 11% of the veterans with the disorder developed new cases of dementia over the seven-year study period, compared with about 7% of those who did not have a post-traumatic stress disorder diagnosis.
Even when researchers filtered out for potentially confounding factors such as other brain injuries and depression, the risk remained nearly double for the veterans with post-traumatic stress disorder.
Unfortunately, Yaffe said, researchers do not yet understand the relationship between the two disorders.
"It is critical that we identify the mechanisms," she said.