Traumatic brain injury can possibly increase the risk of dementia, according to two new studies presented at the Alzheimer's Association International Conference in Paris.

One study showed that aging veterans who had had traumatic brain injury (TBI) had a two-fold increase in the risk of developing dementia, according to Kristine Yaffe, professor of psychiatry, neurology and epidemiology at the University of California, San Francisco and director of the memory disorders program at the San Francisco Veteran's Administration Medical center. She and other researchers looked at medical records of 281,540 veterans age 55 years and older who received care through the Veterans Health Administration and did not have a dementia diagnosis at the start of the decade-long study. The risk of dementia was 15.3% in those with a TBI diagnosis compared with 6.8% in those without one. Approximately 2% of older veterans had a TBI diagnosis during the study period.

In a news release, Prof. Yaffe noted that TBI is common and not only among veterans—about 1.7 million have a TBI each year, mostly due to falls and car crashes. She suggested that "older adults who experience a TBI should be monitored for signs of cognitive impairment following their injuries."

Swelling, and the destruction of axons and neurons, could all be ways that TBI increases the risk of dementia, the researchers suggested.

In another study presented at the conference, researchers at Loyola University Medical Center in Chicago noted that 35% of more than 500 retired football players who were sent an Alzheimer's screening survey had scores suggesting possible dementia. By comparison, only 13% of Americans over the age of 65 has Alzheimer's.

The researchers performed extensive testing on some of these athletes and compared the results with people who did not play professional sports. Their conclusion, which they called "preliminary," was that the athletes had a very high rate of cognitive impairment compared to the general population, expressed at a younger age, and that the cause could be repetitive head trauma.