Bidirectional link found between depression and memory decline in older adults

A recent study published in JAMA Network Open has shed light on the relationship between depressive symptoms and memory decline in older adults. By examining data spanning 16 years, researchers have identified a bidirectional link: depressive symptoms can lead to memory decline, while poorer memory can subsequently increase depressive symptoms.

The aging process often brings about subtle cognitive declines in older adults, and in more severe cases, it can lead to conditions like mild cognitive impairment or dementia. Simultaneously, depressive symptoms are prevalent in older adults, often triggered by severe life events or underlying health conditions.

Both cognitive decline and depressive symptoms are frequently observed together in this age group. Given their co-occurrence, understanding whether one influences the other—or if there is a bidirectional relationship—can help improve treatment and care strategies for older adults.

The researchers utilized data from the English Longitudinal Study of Aging, which includes a representative sample of adults aged 50 and older in England. This study tracked participants over a 16-year period, from 2002 to 2018, ensuring a robust dataset for analysis.

The study began with 11,391 core members, eventually narrowing down to 8,268 participants who had complete data for cognitive function and depressive symptoms assessments. Cognitive functioning was measured using memory recall tests and verbal fluency tests. Memory recall involved remembering a list of 10 unrelated words immediately and after a short delay, while verbal fluency was assessed by asking participants to name as many animals as they could in one minute.

Depressive symptoms were measured using an eight-item version of the Center for Epidemiologic Studies Depression Scale, which asked participants about their depressive symptoms in the past week. This scale provided a score ranging from 0 to 8, with higher scores indicating more severe depressive symptoms.

The researchers found that higher levels of depressive symptoms at the beginning of the study were linked to poorer memory and a faster rate of memory decline over the 16-year period. Poorer memory at baseline, on the other hand, was associated with higher levels of depressive symptoms over time. This indicates that not only can depression impact memory, but memory problems can also worsen depression.

“It is known that depression and poor memory often occur together in older people, but what comes first has been unclear,” said senior author Dorina Cadar of University College London. “Our study shows that the relationship between depression and poor memory cuts both ways, with depressive symptoms preceding memory decline and memory decline linked to subsequent depressive symptoms. It also suggests that interventions to reduce depressive symptoms may help to slow down memory decline.”

While depressive symptoms at baseline were linked to poorer verbal fluency, there was no evidence that depressive symptoms influenced changes in verbal fluency over time. In contrast, baseline verbal fluency did not significantly predict changes in depressive symptoms.

Lead author Jiamin Yin, who graduated from University College London and is now a doctoral student at the University of Rochester, New York, explained: “These findings underscore the importance of monitoring memory changes in older adults with increasing depressive symptoms to identify memory loss early and prevent further worsening of depressive function. It is also critical to address depressive symptoms among those with memory decline to protect them from developing depression and memory dysfunction.”

The study controlled for age, sex, education, wealth, long-standing illness, self-rated health, smoking status, alcohol consumption, and physical activity to account for potential confounding factors in the relationship between depressive symptoms and cognitive function. But as with all research, there are some limitations.

First, a significant number of participants were lost to follow-up, often due to death, potentially skewing the results. These participants were typically older, less educated, and in poorer health, which might mean that the true extent of the associations observed could be more pronounced.

Moreover, depressive symptoms were measured broadly, without distinguishing between different types of depressive symptoms, which could have varying impacts on cognitive functions. Future research could benefit from exploring these nuances in greater detail.

Another limitation was the shorter follow-up period for verbal fluency compared to memory. More extended follow-up periods could provide a clearer picture of the relationship between depressive symptoms and verbal fluency.

Cadar added: “Depression can cause changes in brain structures, such as the hippocampus, which is critical for memory formation and retrieval. Chronic stress and high levels of cortisol associated with depression can damage neurons in these areas. However, a further understanding of mechanisms linking memory decline and depression is crucial for developing targeted interventions aimed at improving mood and slowing cognitive decline in individuals with depression and memory impairment.”

The study, “Bidirectional Associations of Depressive Symptoms and Cognitive Function Over Time,” was authored by Jiamin Yin, Amber John, and Dorina Cadar.