Mediating Effect of Non-Exercise Estimation of Cardiorespiratory Fitness on Relationship Between Physical Comorbidity and Depression in Korean Adult Cancer Survivors

To determine relationship between physical comorbidity (PC) and depression in Korean adults’ cancer survivors and understand if non-exercise estimation of cardiorespiratory fitness (eCRF) might have a mediating effect on such relationship. Data of 448 cancer survivors aged 20–64 years old in Korean National Health and Nutrition Examination Survey Ⅶ-Ⅷ (2016–2020) were analyzed. Depression was assessed with a 9-item Patient Health Questionnaire (PHQ-9). Subjects were categorized into two groups: normal and depression. PC was defined if a participant was diagnosed by a physician or was being treated at the time of the survey. eCRF was determined with sex and age-specific algorithms. In the mediation model, PC (β = 1.836, 95%CI: 1.577 to 2.095, p  < 0.001) was significantly association with depression and eCRF levels mediated (indirect effect = 0.094, bootstrap 95%CI: 0.028 to 0.146) this association. Mediation analysis showed a significant, direct, and indirect effect with a significant Sobel test value (z = 2.517, p  = 0.011). The relationship between PC and depression was significantly mediated by eCRF levels. Early physical activity interventions might prevent depression in cancer survivors with chronic diseases.