Durham, NC — In male veterans, having at least one traumatic brain injury is linked to having lower cognitive scores in later life, according to a twin study.
The study published in the journal Neurology examined the association between lifetime traumatic brain injury (TBI) and cognitive decline in male twins, since twins share many genes and environmental factors, according to the authors.1
Each year, 64 to 74 million people worldwide are affected by TBIs, with the highest incidence occurring before age 30 and in those 70 and older, the study reported. Traumatic brain injuries are associated with an increased risk of Alzheimer’s disease and other dementias, but it’s unclear whether lifetime TBIs influence cognitive trajectories in later life. Cognitive interventions following traumatic brain injuries might improve cognitive trajectories and delay dementia, the researchers suggested.
The participants were male members of the National Academy of Sciences National Research Council’s Twin Registry, a national twin registry of WWII veterans who were born between 1917 and 1927. This twin registry was created in the 1950s using vital statistics records. The cognitive function and traumatic brain injury data for this study were collected as part of the Duke Twins Study of Memory and Aging, in which previous investigators collected cognitive information from the twins in both telephone and in-person interviews beginning in 1990. Of 8,662 study participants, among whom 7,188 individuals were members of twin pairs, 25% reported traumatic brain injury, the researchers pointed out.
The study authors, who analyzed the association between TBI and cognitive status for these participants, are affiliated with San Francisco VAMC in San Francisco; Duke University Medical Center in Durham, NC; and University of California, San Francisco in San Francisco.
“Our study showed that veterans who reported having at least one traumatic brain injury or TBI as we commonly referred to, at any time in their life, had lower cognitive scores in later life compared to their twin sibling who did not experience a TBI,” lead author Marianne Chanti-Ketterl, PhD, MSPH, told U.S. Medicine. “But what is really unique about our results is that our study showed a faster rate of cognitive decline among twins with a) more than one TBI, b) those whose TBI resulted in a loss of consciousness and c) those who experienced the TBI after age 24”. Chanti-Ketterl is an assistant professor in psychiatry and behavioral sciences at Duke University School of Medicine and a senior fellow in the Center for the Study of Aging and Human Development at Duke University Medical Center in Durham, NC.
Lowers Cognitive Reserve
“Our results suggest that TBI both lowers cognitive reserve (i.e., cognitive level) and quickens the pace of cognitive decline, which also suggests that age of exposure may matter for cognitive decline in later life,” Chanti-Ketterl said. “Knowing this information may help physicians identify individuals who may benefit from early interventions that may slow cognitive decline and potentially delay or prevent the onset of dementia.”
Healthcare providers who are treating patients with traumatic brain injury or cognitive decline “should take their time to do a thorough cognitive baseline assessment, which is crucial to detect future cognitive changes,” the researchers recommended. If healthcare providers are “unable to complete a good cognitive baseline assessment due to time restrictions, they should consider referring the patient to a neuropsychologist, if possible. Based on protocol, they should continue with a close follow-up,” according to the authors.
“We were able to quantify that TBI quickens the pace of cognitive decline,” Chanti-Ketterl said. “This evidence has the potential to help healthcare providers identify individuals who may benefit from early interventions that may slow cognitive decline and potentially delay or prevent the onset of dementia. With almost six million people in the United States suffering from dementia, finding things to protect our brains is imperative for healthy aging.”
This analysis studied twins, because twin studies allow researchers to control for early life exposures and genetics, which aren’t known in most studies and can’t be reliably measured in other non-twin studies of late-life cognitive decline, Chanti-Ketterl explained. The vast diversity in “cognitive reserve, genetic risk for neurodegenerative conditions and underlying comorbidities complicate the degree to which researchers can predict risk of cognitive decline in late life attributable to a single factor such as traumatic brain injury,” she added.
“Results obtained from twin design studies support a causal nature of a relationship, in this case the relationship between TBI and cognition, by accounting for twin pair differences in the TBI exposure,” Chanti-Ketterl wrote.
Chanti-Ketterl’s research is focused on factors that have the potential to prevent or delay the onset of dementia. Previous work by her colleagues has shown that traumatic brain injury was associated with dementia, but it’s unknown if scientists would be able to see cognitive changes that did not meet the threshold for dementia, she said.
“Finding that TBIs do contribute to cognitive changes in later life above and beyond genetics and other medical conditions hopefully provides the supportive evidence needed to encourage people to be proactive and protect their heads to avoid future injuries,” Chanti-Ketterl suggested.
Limitations of the study include that most of the participants were white, so the researchers weren’t able to account for racial differences. Study authors did observe that twins with TBIs experienced more medical conditions throughout life than twins without traumatic brain injuries, however, Chanti-Ketterl explained.
- Chanti-Ketterl M, Pieper CF, Yaffe K, Plassman BL. Associations Between Traumatic Brain Injury and Cognitive Decline Among Older Veteran Men – A Twin Study. Neurology. 2023 Sep 6:10.1212/WNL.0000000000207819. doi: 10.1212/WNL.0000000000207819. Epub ahead of print. PMID: 37673685.