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Did you know that after 70 years of age, your chances of developing a mood disorder such as depression or anxiety doubles every five years? The same is true for cognitive decline such as impaired memory. Here's another fun statistic to look forward to: By age 85, one in four of us will have the luxury of suffering from both conditions simultaneously.

But researchers are trying their best to prevent this from happening. And whereas previous research has already shown a link between “affective” disorders (psychiatric disorders such as anxiety and depression) and dementia in aging adults, few studies have focused on how affective disorders may begin to affect cognitive decline prior to a full blown dementia diagnosis.

Now, however, thanks to a new study out of the U.K., published in the Journal of Psychological Medicine, researchers completed a systemic review of thousands of studies and have determined that there is a "significant" link between depression and a decline in cognitive function in older adults.

Since a decline in cognitive abilities has been associated with poorer quality of life overall, both financially and emotionally, this study makes the case for close monitoring of cognitive abilities in those diagnosed with major depressive disorder throughout the entire life span so they can be monitored and treated early on.

According to the study’s authors, people with affective disorders such as depression have been shown to commonly have cognitive symptoms such as impairments in memory, executive control, feedback sensitivity and affective processing. The regions of the brain associated with cognitive difficulties include the prefrontal cortex, subcortical regions and temporal lobe structures.

As a result of the average rate of cognitive decline in persons over 70 to double every five years, researchers examined the rate of cognitive decline in study participants over the course of one year.

The current study’s authors go on to write that previous studies that looked at affective disorders and cognitive decline had inconsistent methodologies and study designs and that there have been no systemic studies done on this topic.

 

The researchers conducted their systematic review using studies written in English up to November 2016 from PubMed, PsycInfo, Cochrane, and ScienceDirect databases with keywords related to affective problems, describing the decline in cognitive state, and related to methodology. Studies had to contain at least 100 participants in order to be included in the current review.

After screening 25,844 studies for relevancy, researchers ended up with 34 eligible studies for their review - 32 on depression and five on anxiety looking at the link between the particular affective disorder and a decline in cognitive state. For the studies on depression, the average age of participants was 72 and 59 per cent of participants were female from the United States, the Netherlands, Taiwan, Australia, Canada, France, Germany, England, Italy, and Japan. Unfortunately, there weren't enough studies on anxiety to be included for the review.

Scales used to measure depression for the review included the Center for Epidemiologic Studies Depression Scale, the Geriatric Depression Scale, the Diagnostic Interview Schedule, the Neuroticism scale, the Duke Depression Evaluation Schedule, the Goldberg Depression Scale, the Neuropsychiatric Inventory, the Hamilton Rating Scale for Depression, and the Symptom Checklist. 

The results of the systematic review revealed that individuals with depression “were at an increased risk of a greater decline in cognitive state.”

“Our results extend these findings by linking affective problems to a greater decline in cognitive state in samples without dementia at baseline,” write the study's authors.

The researchers propose three major hypotheses to explain the potential association between depression and a decline in cognitive state. The first is that depression may pose as a risk factor by “lowering the threshold for manifesting decline”; the second theory points purports that perhaps depression and other affective disorders are in fact an early symptom of dementia; and the third hypothesis is that though depression and a decline in cognitive state may be two entirely separate processes, they may share “common risk factors and underlying neurobiological substrates.”

“These hypotheses are not necessarily mutually exclusive,” note the study's authors, “and it is likely that multiple pathways and mechanisms underlie this relationship.”

Researchers indicate the biological and behavioural pathways between the two could be a result of vascular disease, increased cortisol production leading to “atrophy of the hippocampus” in the brain among others and that lifestyle could also play a role including one’s level of education, social support, early life adversity, amount of exercise, alcohol consumption, smoking, and medication.

“It is more likely that a complex interaction of biological and sociobehavioural mechanisms are involved in linking affective problems with cognitive decline,” note the study's authors, “rather than one single aetiological determinant.”

Researchers hope that future studies will examine how to stop the decline in cognitive state as a result of depression through effective methods of treatment and disease management.

“Given the predicted increase in population size of adults over the age of 65, as well as the poor outcomes and economic costs associated with a decline in cognitive state and impairment,” conclude the study authors, “it is important to identify life course risk factors for poorer late-life cognitive outcomes, for potential early intervention.”

 

REFERENCE:

John A, Patel U, Rusted J, Richards M, Gaysina D (2018), Affective problems and decline in cognitive state in older adults: a systematic review and metaanalysis, Psychological Medicine 1–13, https:// doi.org/10.1017/S0033291718001137