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New research shows that suffering concussions — or even just one — is linked to increased cognitive decline later in life, including in patients who appeared to have fully recovered from the injury.

The research, published in the journal Neurology, followed thousands of twins who were World War II veterans, many of them identical. Since identical twins share genetic code, comparing the development of one twin who suffered a concussion to another who didn't provides the closest medical "what if?" scenario that science can get.

In total, 8,662 men participated in the study, most with their twins. They took cognitive tests administered over the phone, starting at around the average age of 67, and took followup tests up to three times over the next 12 years.

This decades-long effort, which started in the 1990s, found that twins who had a traumatic brain injury (TBI) scored lower on cognitive tests than their counterparts at age 70. Furthermore, the speed of cognitive decline seems to be worsened by having multiple concussions, having a concussion after age 24, or having a concussion that resulted in loss of consciousness (or, we shudder to consider, all of the above).

"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," said co-author Marianne Chanti-Ketterl, a gerontologist at Duke University, in a statement about the research.

Like with any study, there are some caveats.

Notably, most of the participants were white and male. And while the researchers controlled for factors like education, neurological diseases, and drinking and smoking habits, they did not control for others like physical activity. Nor did the research distinguish between the severity of the concussions.

Also worthy of note is that these injuries were self-reported. As such, the possibility of erroneously recalled injuries can't be ruled out.

Still, the findings are likely to be significant. An epidemiologist who peer-reviewed the study told The Washington Post that they "do not know of any others that use a twin-study design." It's a study that — ironically — is without parallel.

Followup research will have to bear out the study's findings. But for now, its implications are clear: take care of your brain. And see a doctor if you have a head injury, because many events in everyday life, like fender benders, can cause a concussion.

"With the trend we are seeing with increased emergency room visits due to sports or recreation activity injuries, combined with the estimated half million members of the military who suffered a TBI between 2000 and 2020, the potential long-term impact of TBI cannot be overlooked," Chanti-Ketterl said. "These results may help us identify people who may benefit from early interventions that may slow cognitive decline or potentially delay or prevent dementia."

More on brain science: Mitch McConnell's Doctor Says His Brain Scans Are Clear

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