Physical Activity Mediates the Effects of Depressive Symptoms on the Cognitive Function of Older Adults

Background and Purpose: Past studies have found that depressive symptoms were either associated with cognitive impairment or have an effect on cognitive decline over time (Wilson et al., 2004; Sachs-Ericsson et al., 2005; Ganguli et al., 2006). Hence, older adults who experience late life depression could have a higher risk of developing cognitive impairment or have more rapid cognitive decline over time. Some studies have shown that physical activity was associated with lower risk of cognitive decline or have a positive effect on cognitive function (Vance et al., 2005; Sofi et al., 2010; Groot et al., 2015). The purpose of this study is to examine whether physical activity could mediate the effects of depressive symptoms on cognitive function.

Methods: This study used a sample of individuals older than 60 years (N=9,753) from the 2014 Health and Retirement Survey (HRS). The dependent variable cognitive function was based on the modified Telephone Interview for Cognitive Status (TICS). This measure of cognitive function included a word recall test for memory, the serial seven subtraction test for working memory, and backward counting test for attention and processing speed. Depressive symptom was a sum score from the Center for Epidemiologic Studies Depression Scale (CES-D). Survey respondents were asked about the type and frequency of physical activity that they participated in. Physical activities were categorized as vigorous, moderate, and mild. For each type of physical activity, respondents were asked how frequent they participate in these activities, i.e. every day, more than once a week, one to four times a month, and hardly ever or never. Hierarchical regression analysis was conducted to examine the relationship between depressive symptoms, physical activity, and cognitive function. Mediation analysis was used to examine whether physical activity mediated the effects of depressive symptoms on cognitive function.

Results: Regression results indicated that experiencing more depressive symptoms was associated with poorer cognitive function, while participating in moderate and mild physical activity were associated with better cognitive function. Mediation analysis indicated that the direct effect of depressive symptoms on cognitive function was significant. The indirect effect of depressive symptoms on cognitive function mediated by moderate and mild physical activity were also significant, demonstrating that physical activity is a significant mediator of the effects of depressive symptoms on cognitive function.

Conclusions and Implications: Findings suggest that physical activity could potentially improve the cognitive function of older adults who have depressive symptoms. Moderate and mild physical activity could benefit older adults with depressive symptoms and reduce the risk of cognitive decline. Frail, disabled or chronically ill older adults are less likely to participate in vigorous physical activity, but they could benefit from participating in moderate or mild physical activity and have better cognitive health.