Anxiety among the middle-aged could be linked with dementia later in life, researchers have said.
An analysis of existing data found an association between moderate to severe mid-life anxiety and future incidence of the neurological disorder, according to research published in journal BMJ Open.
The authors, from the University of Southampton and University College of London, said the effect of treating anxiety on the development of dementia "remains an open question".
Experts warned the results do not mean that anxiety causes dementia and should be treated with caution.
The researchers examined evidence from four studies involving nearly 30,000 people, all of which found a link between moderate to severe anxiety and dementia in later life, with a gap of at least 10 years in between diagnoses.
An abnormal stress response, typical of anxiety, could speed up brain cell ageing and degeneration in the central nervous system, the authors suggest, which may increase vulnerability to dementia.
They said: "Whether reducing anxiety in middle age would result in reduced risk of dementia remains an open question.
"The effect of treatment of anxiety using pharmacological and non-pharmacological therapies during midlife on later risk for dementia has not yet been investigated."
They added: "Given the high prevalence of anxiety seen in primary care, we suggest that general practitioners could consider anxiety alongside depression as an indicator of risk for dementia."
However the authors note further research is needed to assess whether anxiety is a risk factor for dementia or an early symptom of dementia.
Dr James Pickett, head of research at Alzheimer's Society, which part-funded the study, said: "Mental health problems affect many people, and it is crucial that research considers whether their effects could increase our risk of dementia.
"Currently, we don't know enough about anxiety to say whether it is an early sign of the changes in the brain seen in dementia, or if it independently puts people at greater risk of developing the condition.
"What we do know is that changes in the brain can begin more than 10 years before dementia symptoms emerge.
"As well as anxiety, there are other complex mental health issues that can be seen in the early stages of dementia, and we need further research to unpick the relationship between these."
Commenting on the findings, Masud Husain, professor of neurology at the University of Oxford, said: "The results have to be considered with caution.
"They certainly don't mean that all people with anxiety - which is a very common condition - are at higher risk.
"Nor is it clear how anxiety might be linked to dementia."
He added: "These findings don't tell us whether more aggressive treatment of anxiety would lead to reduced risks of developing dementia, but there might be other good health reasons to do this anyway."
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