Dementia is one of the greatest global health challenges. As the world’s population continues to age and to live longer, the number of people affected by dementia is expected to rise to 130 million by 2050. Given that there is no cure for dementia, there’s an urgent need to identify modifiable risk factors to prevent or delay the onset of dementia.
We’ve recently identified post-traumatic stress disorder (PTSD) as a potential risk factor for developing dementia. PTSD is caused by traumatic experiences such as childhood trauma, war or being the victim of violence or abuse. People with PTSD experience distressing symptoms, often for many years. These symptoms can include flashbacks of the traumatic event, avoiding reminders of the event, hyper-arousal, and memory deficits related to traumatic experiences.
Our study is the first to try and quantify the risk of developing dementia associated with PTSD. We searched through nearly 8,000 papers to identify all existing studies worldwide, across different populations, that examined the relationship between PTSD and future risk of dementia. We only included studies that were conducted over a long period of time to ensure that PTSD was present before the onset of dementia.
We found 13 studies that specifically investigated the link between dementia and PTSD. Studies were conducted on four continents and included data from 1,693,678 people. Apart from one, all studies found that compared with those without the condition, PTSD was associated with an increased risk of developing dementia, based on subsequent follow-ups from one up to 17 years later.
A link between PTSD diagnosis and dementia was found not only in veterans and war-refugees, but also in those with non-combat related traumatic experiences. The link remained even after other factors that could have been influencing the relationship between PTSD and dementia were taken into account. These included a person’s gender, age, physical health (including whether they had certain health conditions, such as blood vessel disease, which is known to increase dementia risk, and other psychiatric conditions, such as depression and alcohol misuse.
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We performed two meta-analyses, a technique that statistically combines results from each study to estimate the overall risk. It revealed that the rate of being diagnosed with dementia in people with PTSD was 1.61 to almost two times the rate in those without PTSD.
However, our review did not investigate the underlying reasons for the association between dementia and PTSD, so these remain unclear. One possibility is that PTSD speeds up cognitive decline in older age. For example, the stress experienced by PTSD symptoms, which may be continuous over many years, may wear down the brain, making it more vulnerable to cognitive decline and dementia. PTSD is also often present with other known risk factors that increase the likelihood of developing dementia, such as depression, social isolation, or higher alcohol intake.
Our study allows us to conclude for the first time that PTSD is a strong and potentially modifiable risk factor for dementia. This research is important as we have been able to identify specific groups of people who are more vulnerable to developing dementia.
Many people with PTSD do not access treatment. This is sometimes due to a lack of mental healthcare services, or because of perceived stigma associated with having a mental health condition. We now have more evidence showing how traumatic experiences – and accessing treatment to deal with them – could have a long-lasting effect on people. Treatment may also influence future risk of developing dementia. However, we don’t yet know whether treating PTSD may reduce the dementia risk, or delay its onset.
As our study has shown, PTSD affects our brain health by increasing vulnerability to dementia. An important question is how, and whether we could learn from these findings, to develop preventative treatments for those with greater risk.
Vasiliki Orgeta has received funding from Alzheimer's Society. No other known conflicts of interest.