Scientists say they have identified a clear link between post-traumatic stress disorder (PTSD) and dementia.
Researchers at University College London (UCL) believe the link is twice as likely in the general population than in members of the Armed Forces and veterans.
The research data comes from 13 separate studies across 13 different countries, and while PTSD may increase the risk of dementia, it is less likely to develop in Armed Forces personnel and veterans due to the treatment they receive.
It is unclear why PTSD would lead to dementia, but the UCL study suggests the symptoms could flood the brain with stress hormones.
In an interview with Forces News, Dr Vasiliki Orgeta, a researcher at UCL, said: "Stress could be causing significant… brain changes over many years," and making the brain itself "more vulnerable".
Dr Orgeta also said these changes could also be related to "behavioural changes".
"You could be socially isolated because you are experiencing PTSD. You may have less access to employment after leaving, for example, the Armed Forces," she added.
The study also found that veterans with PTSD were only one and a half times more likely to develop dementia than veterans without PTSD.
In the general population, PTSD may not be diagnosed as quickly as it is in veterans and may have been caused by historic events, such as a trauma in childhood.
Mia Maria Gunak, the lead researcher at UCL, told Sky News the research found that "people with PTSD face a 61% higher risk of developing dementia" while, in another study with different methods, it was found the risk doubled.
Dr Orgeta is urging more research into how treatment could reduce the risk of dementia in later life.
PTSD is an anxiety disorder caused by very stressful, frightening or distressing events.
The NHS estimates it can affect one in three people who have had a traumatic experience.
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