Researchers at the University of Sussex in the UK conducted a robust systematic review of 34 longitudinal studies, with the focus on the link between depression or anxiety and decline in cognitive function over time.

The study combined and reviewed evidence from over 71,000 participants, and included people who presented with symptoms of depression as well as those that were diagnosed as clinically depressed.

Researchers looked at the rate of decline of overall cognitive state - encompassing memory loss, executive function (such as decision making) and information processing speed - in older adults.

The study found that people with depression experienced a greater decline in cognitive state in older adulthood than those without depression.

As there is a long pre-clinical period of several decades before dementia may be diagnosed, the findings are important for early interventions as currently there is no cure for the disease.

"This study is of great importance - 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 thirty years," said Darya Gaysina from the University of Sussex.

"Our findings should give the government even more reason to take mental health issues seriously and to ensure that health provisions are properly resourced”.

"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 said.