An analysis of existing data found an association between moderate to severe midlife 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 warn the results do not mean 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.

"Whether reducing anxiety in middle age would result in reduced risk of dementia remains an open question," they said.

"The effect of treatment of anxiety using pharmacological and non-pharmacological therapies during midlife on later risk for dementia has not yet been investigated.

"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.

Commenting on the findings, Masud Husain, a 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."

Australian Associated Press