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Published on: May 14, 2019
by Women’s Brain Health Initiative:
Traumatic brain injury (TBI), post-traumatic stress disorder (PTSD), and depression have been associated with an increased risk of developing dementia, either each on its own or in combination with one another. This is of particular concern for military veterans because they are more likely than civilians to experience any or all of these risk factors. This article reviews what is currently known about the relationship between dementia and TBI, PTSD, and depression in the veteran population.
Veterans & TBI
TBI is a severe or moderate trauma to the head, where physical portions of the brain are damaged and functioning is impaired. There is growing evidence that TBI is associated with a variety of short- and long-term adverse health outcomes.
In one study published in 2014 in Neurology, the researchers sought to determine whether TBI is independently associated with the risk of incident dementia in older veterans after accounting for the competing risk of mortality and adjusting for potential confounders. The researchers analyzed data from the medical records of over 188,000 U.S. veterans aged 55 years or older. None of the participants had a dementia diagnosis at baseline.
“We found that during the nine-year follow-up period, 16% of participants with TBI developed dementia compared with 10% of those without TBI,” explained Dr. Kristine Yaffe, a professor of psychiatry, neurology, and epidemiology at the University of California, San Francisco, and one of the authors of the study. In other words, older veterans with TBI were 60% more likely to develop dementia, and their age of dementia onset was approximately two years earlier than those without TBI.
Veterans & PTSD
PTSD is a common psychiatric syndrome associated with high rates of morbidity and mortality, and is one of the most common conditions in veterans returning from combat. The prevalence of PTSD is much higher among veterans (12% to 31%) than it is among the general population (7%). Multiple studies have found that veterans with PTSD are nearly twice as likely to develop dementia than veterans without PTSD.
The first study to demonstrate a link between PTSD and risk of dementia in the veteran population was conducted by Dr. Yaffe and colleagues, and published in June 2010 in Archives of General Psychiatry. In this study, the researchers analyzed the medical records of over 181,000 U.S. veterans aged 55 years or older (96.5% men), none of whom had a dementia diagnosis at baseline. “We found that the cumulative incidence rates of dementia were significantly higher for veterans with PTSD than those without the condition,” said Dr. Yaffe.
“Over an average follow-up period of 7.2 years, 10.6% of those with PTSD developed dementia, whereas 6.6% of those without PTSD did.” After adjusting for important differences between those with and without PTSD (such as demographics, as well as medical and neuropsychiatric comorbidities), the researchers concluded that the veterans with PTSD had almost double the risk of developing dementia compared to those without PTSD.
“Given how much more common PTSD is among veterans than the rest of the population, this finding of increased risk of dementia is of particular concern,” emphasized Dr. Yaffe. “It is important that those with PTSD are treated, and that they are screened for cognitive impairment as they age.”
Veterans & Depression
Dr. Yaffe and colleagues conducted another study to investigate how dysthymia and depression affect the risk of dementia and mortality among older U.S. veterans. They analyzed the medical records of over 281,500 veterans aged 55 years or older, predominantly men, all of whom did not have dementia at baseline. Approximately 10% of the participants had a diagnosis of depression at baseline and almost 1% had dysthymia.
“We found that, over the follow-up period of an average of 7.2 years, patients with dysthymia or depression were twice as likely to develop dementia compared to participants without either of these diagnoses,” explained Dr. Yaffe. “Our findings demonstrate that even a mild form of depression is linked with increased risk of dementia.”
These findings were published in the August 2012 issue of American Journal of Geriatric Psychiatry.
Multiple Risk Factors
It is not uncommon for veterans to have more than one of these three conditions.
Veterans who have been diagnosed with TBI are more likely to also be diagnosed with PTSD, and have an increased risk of developing depression. PTSD also commonly co-occurs with depression. A large meta-analysis published in 2013 reported that 52% of individuals with current PTSD also had major depressive disorder. That percentage was higher among the subset of participants from the military.
The presence of multiple risk factors appears to heighten the risk of dementia. Dr. Yaffe and colleagues, for instance, found that the risk of dementia increased in an additive manner when TBI was combined with other medical and psychiatric comorbidities, including PTSD and depression.
Research on Female Veterans
To date, only a handful of studies about the relationship between dementia and TBI, PTSD, and/or depression in the veteran population have included female participants. Recently, Dr. Yaffe and colleagues sought to address this research gap by exploring the risk of dementia among female veterans specifically. Their findings were published in December 2018 in Neurology.
“We felt that it was important to learn about how these conditions affect women in particular, as women are joining the military in increasing numbers and more are taking on combat roles, and because women may be at greater risk for some of these conditions than men.”
The researchers reviewed the medical records of over 109,140 female veterans aged 55 years or older to identify who had a diagnosis of TBI, PTSD, or depression at baseline. There were approximately 81,135 women who had none of the conditions; 20,410 who had depression only; 1,363 with PTSD only; 488 with TBI only; and 5,044 with more than one condition. None of the women had dementia when the study began.
Over an average four-year follow-up period, 4,125 of the participants (4% of the entire group) developed dementia. Consistent with previous findings from research on the general public and male veterans, the researchers found a relationship between TBI, PTSD, or depression and incidence of dementia in this group of women. “After adjusting for demographics and medical conditions, we found that women with TBI, PTSD, or depression had a significant increase in risk of developing dementia compared to women without these diagnoses,” explained Dr. Yaffe. “Women with one of these military-related risk factors had between a 50% and 80% increase in risk of developing dementia, while women with multiple risk factors had double the risk.”
It is important to note, however, that although the study shows an association between these three conditions and dementia risk, it does not prove that there is a cause-and-effect relationship.
Additionally, the researchers used official diagnoses noted in the medical records in order to determine which participants had the various conditions. It is possible that there were additional women with these conditions, but had not been diagnosed because they exhibited less severe symptoms.
Finally, the overall risk for women veterans to develop dementia is low, even if TBI, PTSD, or depression is present. “Among the participants who had none of these conditions, 3.4% developed dementia, compared to between 3.9% and 5.7% for women who had any of the three conditions,” explained Dr. Yaffe.
“I want to emphasize to female veterans that if they have one of these conditions, it is certainly not inevitable that they will develop dementia,” Dr. Yaffe continued.
“These percentages demonstrate that while having TBI, PTSD or depression does increase risk of dementia, the vast majority of female veterans – with or without these conditions – will not develop dementia.”
“The findings from our various studies highlight the need for increased screening for TBI, PTSD, and depression among veterans, both female and male. Diagnosing and treating these conditions might help to reduce dementia risk.”
Source: MIND OVER MATTER V8
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