The Mediating Role of Depression in the Relationship Between Physical Activity and Quality of Life Among Patients with Coronary Heart Disease

Background: Depression, a known comorbidity in coronary heart disease (CHD), is associated with adverse cardiac events, mortality, symptom burden, physical limitation, and poor quality of life (QOL). Evidence has shown that depression impedes self-care behaviors, including physical activity. Similarly, regular physical activity has been shown to lessen depressive symptoms and improve cardiovascular health. Objective: The aim of our study was to investigate the direct effect of depressive symptoms on physical activity and QOL. We also sought to investigate the mediator effects of physical activity and depressive symptoms on QOL and to test the moderator effects of depressive symptoms on physical activity and QOL. Methods: In this cross-sectional study, 20-year follow-up survey data were collected from 126 survivors from the Heart and Soul prospective cohort study. A mediation test was conducted using the steps described by Baron and Kenny. Results: Physical activity significantly predicted QOL (β = 0.13, P = .02) and significantly predicted depressive symptoms (β = −0.19, P < .001). Depressive symptoms significantly predicted QOL (β = −0.76, P < .0001). The average causal mediation effect was statistically significant (0.15, P < .001). Depression was not a moderator of physical activity and QOL. Conclusions: This study demonstrated that depression mediated the effect of physical activity on QOL. Identifying and treating depressive symptoms simultaneously while addressing physical activity may be of importance to improving QOL in patients with chronic CHD.