The new research was carried out by a team of scientists led by Amy Gimson, a researcher at the University of Southampton's Faculty of Medicine in the United Kingdom.
Gimson and her colleagues observed that more and more studies were highlighting a link between mental health problems and late-onset dementia — the most prevalent form of dementia, which affects people around the age of 65.
For instance, the authors of the new study write that depression has been shown to boost the risk of Alzheimer's by almost twofold.
Anxiety often occurs together with depression, and symptoms of anxiety have often been reported by people years before receiving a diagnosis of dementia.
But until now, it has remained unclear whether these associations mean that anxiety and depression are the first symptoms that appear before the full-blown form of dementia develops, or whether anxiety and depression are independent risk factors.
So, to investigate this, Gimson and her team sifted through 3,500 studies in search of papers that examined the link between midlife depression, with or without anxiety, and late-onset dementia.
The findings of their meta-analysis were published in the journal BMJ Open.
Anxiety — a risk factor for dementia
Of the body of research examined, only four studies focused on the desired topic; these studies accounted for potential confounders such as vascular and psychiatric conditions, and demographic factors.
The researchers were unable to carry out a pooled analysis of these four studies because they were designed so differently, but the authors mention that the methods used in the studies were reliable and their conclusions solid.
Additionally, the combined sample size of the four studies was large, including almost 30,000 people.
All four studies found a positive correlation between moderate to severe anxiety and later development of dementia: "Clinically significant anxiety in midlife was associated with an increased risk of dementia over an interval of at least 10 years," write the researchers.
These findings suggest that anxiety may be an independent risk factor for late-onset dementia, excluding the anxiety that might represent the initial symptoms of dementia, write Gimson and colleagues.
The link between anxiety and dementia, the authors note, may be explained by the excessive stress response triggered by the mental health condition.
This abnormally high stress response might accelerate the aging process of brain cells, which, in turn, may speed up age-related cognitive decline.
Relieving anxiety may prevent dementia
If a stress response that is triggered by anxiety is to blame for accelerated cognitive decline, does this mean that alleviating anxiety would keep dementia at bay?
This "remains an open question," the authors write. However, they suggest, non-pharmacological anti-anxiety treatment options are worth trying.
In this regard, Gimson and her colleagues conclude:
"Non-pharmacological therapies, including talking therapies, mindfulness-based interventions, and meditation practices, that are known to reduce anxiety in midlife, could have a risk-reducing effect, although this is yet to be thoroughly researched."