They also had a more rapid decline in those scores than twins who did not have a concussion or traumatic brain injury (TBI).
The team looked at 8,662 male World War II veterans who took a thinking skills test when they were an average age of 67 and then again up to three more times over 12 years.
Scores for the test can range from zero to 50. The average score for all participants at the beginning of the study was 32.5 points.
One in four of the participants had suffered and they were more likely to have lower test scores at age 70.
This was particularly so when they had a concussion where they lost consciousness or were older than 24 when they were knocked out.
Study author Dr. Marianne Chanti-Ketterl said: “These findings indicate that even people with traumatic brain injuries in earlier life who appear to have fully recovered from them may still be at increased risk of cognitive problems and dementia later in life.
“Among identical twins, who share the same genes and many of the same exposures early in life, we found that the twin who had a concussion had lower test scores and faster decline than their twin who had never had a concussion.”
Those twins with traumatic brain injury with loss of consciousness, more than one traumatic brain injury and who had their injuries after age 24 were more likely to have faster cognitive decline than those with no history of traumatic brain injury.
For example, a twin who experienced a traumatic brain injury after age 24 scored 0.59 points lower at age 70 than his twin with no traumatic brain injury, and his thinking skills declined faster, by 0.05 points per year.
These results took into account other factors that could affect thinking skills, such as high blood pressure, alcohol use, smoking status and education.
Dr. Chanti-Ketterl added: “Although these effect sizes are modest, the contribution of TBI on late life cognition, in addition to numerous other factors with a detrimental effect on cognition, may be enough to trigger an evaluation for cognitive impairment.
A limitation of the study was that traumatic brain injuries were reported by the participants, so not all injuries may have been remembered or reported accurately.
Produced in association with SWNS Talker
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