A study of twins who served in World War II found that early-life concussions are associated with lower thinking and memory scores in later life and faster cognitive decline than non-concussed twins.
The research, titled "Associations Between Traumatic Brain Injury and Cognitive Decline Among Older Veteran Men - A Twin Study" published in the journal Neurology, suggests a potential link between traumatic brain injuries (TBI) and cognitive issues in the future.
Early Life Concussions Linked to Long-Term Cognitive Decline and Dementia Risk, Study Finds
Comparing Early Life Conditions of Twins That May Lead to Cognitive Decline
The study primarily involved White male World War II veteran twins and was conducted by Duke University. It commenced in the 1990s and enlisted twins born between 1917 and 1927, who were part of a national registry established in the 1950s.
A total of 8,662 male World War II veterans participated, wherein 7,188 of them participated as twin pairs and 1,474 participated individually. About 25% of the twins disclosed experiencing at least one TBI.
Participants underwent an initial thinking skills assessment at an average age of 67, with up to three subsequent assessments over 12 years. The test scores ranged from zero to 50, with an average starting score of 32.5 points.
Among the 589 pairs of identical twins in the study, those who had experienced at least one traumatic brain injury and had a concussion at age 25 or older exhibited lower scores on cognitive tests later in life. This finding highlights the impact of shared environmental factors during their upbringing and military service.
By examining identical and fraternal twins, researchers can make comparisons among participants while mitigating some, if not all, of the inherent genetic factors and certain early-life circumstances. Identical twins possess identical genetic profiles, whereas fraternal twins share approximately 50% of their genes.
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Traumatic Brain Injury Increases Risk of Faster Cognitive Decline in Old Age
The study assessed participants for TBI, inquiring about the number of TBIs, loss of consciousness due to a TBI, and the circumstances of the injuries. The International Classification of Disease (ICD) defines a mild TBI as a concussion, while a severe TBI encompasses conditions like skull fractures, edema, and brain injuries or bleeds.
TBIs were not further categorized into mild or severe in the study. Cognitive tests were conducted over the phone every three to four years for over 12 years, with questions ranging from general knowledge to arithmetic.
Across all participants, those with at least one TBI, loss of consciousness from head injuries, or injuries occurring at age 25 or older tended to have lower cognitive test scores. Those who experienced loss of consciousness, multiple TBIs, or injuries at age 25 or older also demonstrated a faster cognitive decline in subsequent tests.
The study controlled for factors like alcohol use, smoking, cardiovascular diseases, risk factors, and neurological conditions, but not physical activity or hearing loss.
Funded by the National Institute on Aging and the Defense Department, the study is the first to examine cognition in relation to TBIs over more than a decade of an individual's later life.
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