In the past, studies have linked depression and anxiety to an increased risk of dementia later in life. Now, a comprehensive assessment of more than 30 studies suggests that depression speeds up the brain's aging process.
A paper published in the journal Psychological Medicine is the end product of a meta-analysis involving 34 longitudinal studies examining the association between depression or anxiety and brain aging. In contrast to previous work, the researchers excluded participants diagnosed with dementia before the study. This left more than 71,000 patients with symptoms of depression or a clinical depression diagnosis, who they monitored for signs of cognitive decline, such as memory loss and problems with executive function (e.g. decision making).
"This study is of great importance,” Darya Gaysina, co-lead author from the University of Sussex's EDGE Lab, explained in a statement.
“Our populations are ageing at a rapid rate and the number of people living with decreasing cognitive abilities and dementia is expected to grow substantially over the next 30 years."
While there wasn't enough data to link premature cognitive decline to anxiety, the researchers did find a strong correlation between cognitive decline and depression – people with depression seemed to experience a greater decline in cognitive ability during old age than people without.
However, it is worth pointing out some limitations to the study. First of all, it was a meta-analysis and, therefore, involved multiple studies with potentially different assessments of depression.
Second, preclinical dementia can predate dementia (and symptoms of cognitive decline) by decades but still cause changes to the brain that could indicate reverse causality, i.e. the preclinical dementia causes the depressive symptoms. While patients with a dementia diagnosis were eliminated from the meta-analysis, those with preclinical dementia may have been (unintentionally) included.
The explanation behind this association between depression and cognitive decline is uncertain. Is depression a risk factor? Is depression an early clinical presentation of cognitive decline? Or are depression and cognitive decline two symptoms of a third underlying disorder?
The key takeaway is that there is even more of an incentive to take mental health seriously. Depression, especially, is shockingly common, affecting an estimated one in five people in the UK and one in 12 in the US (though this is probably an underestimate).
“We need to protect the mental wellbeing of our older adults and to provide robust support services to those experiencing depression and anxiety in order to safeguard brain function in later life," Gaysina added.
The silver lining is that cognitive decline is not an inevitable product of depression and the researchers suggest ways in which you can limit the risk. For example, by exercising, practicing mindfulness, and undertaking recommended therapeutic treatments, such as cognitive behavioral therapy – all of which have “been shown to be helpful in supporting wellbeing, which in turn may help to protect cognitive health in older age."