Evidence that psychological problems such as depression and anxiety increase risk for dementia later in life is growing. These problems, known as affective disorders, as well as poor cognitive function are, of course, not unusual in older adulthood.

After age 70, for example, it has been estimated that the both lower mood and poor cognition doubles with every 5 years, and that by age 85, around one in four people experience both these together[1]. But there are important gaps in the understanding of this link - for example the exact order in time of the association is currently unclear.

A new study from psychologists at the University of Sussex[2] is the first study that provides comprehensive evidence for the effect of depression on decline in overall cognitive function (also referred to as cognitive state), in a general population.

Rate Of Cognitive State Decline

The current research involved a meta-analysis of 34 longitudinal studies, with the focus on the link between depression or anxiety and decline in cognitive function over time.

Evidence from more than 71,000 participants was combined and reviewed. Including people who presented with symptoms of depression as well as those that were diagnosed as clinically depressed, the study 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.

Importantly, any studies of participants who were diagnosed with dementia at the start of study were excluded from the analysis. This was done in order to assess more broadly the impact of depression on cognitive aging in the general population.

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.

Possible Reasons

The authors of the study write that there are 3 schools of thought on what the mechanisms behind this link are. The first suggests that affective problems may in fact be a causative risk factor for subsequent decline in cognitive state[3].

A second hypothesis is that affective problems could acting as a prodromal feature of dementia, where affective problems may be an early clinical presentation of cognitive decline. In that case, cognitive decline and affective problems would be seen as different symptoms of the same underlying condition.

Finally, affective problems and decline in cognitive state could be separate processes while share common risk factors and underlying neurological bases.

“There are several biological and behavioural pathways which may be involved in the association between affective problems and decline in cognitive state. These include vascular disease, increased cortisol production leading to atrophy of the hippocampus (Geerlings and Gerritsen, 2017), increased deposition of β-amyloid plaques (Byers and Yaffe, 2011), inflammatory changes (Byers and Yaffe, 2011) and a decline in the levels and activities of neurotrophic factors (Royall et al., 2017). A multiple pathways model has also been proposed by Butters et al. (2008), which posits that depression-associated cerebrovascular disease and glucocorticoid neurotoxicity may operate to decrease levels of brain and cognitive reserve, as well as interact with pathology of Alzheimer’s disease, giving rise to the clinical manifestation of Alzheimer’s disease and accelerated cognitive decline,"

the authors add.

“Depression is a common mental health problem – each year, at least 1 in 5 people in the UK experience symptoms. But people living with depression shouldn’t despair – it’s not inevitable that you will see a greater decline in cognitive abilities and taking preventative measures such as exercising, practicing mindfulness and undertaking recommended therapeutic treatments, such as Cognitive Behaviour Therapy, have all been shown to be helpful in supporting wellbeing, which in turn may help to protect cognitive health in older age,"

said researcher Amber John, who carried out this research for her PhD at the University of Sussex.

[1] Arve S et al. (1999) Coexistence of lowered mood and cognitive impairment of elderly people in five birth cohorts. Aging (Milan, Italy) 11(2), 90–95

[2] A. John, U. Patel, J. Rusted, M. Richards, D. Gaysina. Affective problems and decline in cognitive state in older adults: a systematic review and meta-analysis. Psychological Medicine, 2018; 1 DOI: 10.1017/S0033291718001137

[3] Bennett, S and Thomas, AJ (2014) Depression and dementia: cause, consequence or coincidence? Maturitas 79(2), 184–190

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