Non-exercise estimation of Cardiorespiratory fitness as a mediator in the relationship between physical comorbidity and depression among Korean cancer Survivors: Evidence from KNHANES 2016–2020

This study aims to explore the relationship between physical comorbidity (PC) and depression among Korean adult cancer survivors, investigating the potential mediating role of non-exercise estimation of cardiorespiratory fitness (eCRF). Data from 448 cancer survivors aged 20–64 years participating in the Korean National Health and Nutrition Examination Survey Ⅶ–Ⅷ (2016–2020) were analyzed. Depression was assessed using the 9-item Patient Health Questionnaire (PHQ-9). Subjects were categorized into two groups: normal and depression. PC was defined as a participant diagnosis by a physician or treatment at the time of the survey. eCRF was determined using sex and age-specific algorithms. A higher number of PC and lower eCRF were associated with an increased risk of depressive symptoms in cancer survivors. Additionally, the mediation analysis showed that eCRF mediated the relationship between PC and PHQ-9 scores (indirect effect = 0.013, bootstrap 95 %CI = 0.006 to 0.021), even after adjusting for covariates. The total effects of PC on the PHQ-9 score was 8.4 %, explaining the relationship. These findings highlight the importance of regular physical activity to enhance cardiorespiratory fitness, a critical component of holistic survivorship care. Early physical activity interventions should be integrated into clinical practice to prevent depression in cancer survivors with chronic diseases. • Cancer survivors' depression is linked to physical comorbidities and low cardiorespiratory fitness (CRF). • Non-exercise CRF estimation mediates the effect of comorbidities on depressive symptoms. • Enhancing CRF may mitigate depressive symptoms in cancer survivors with chronic diseases. • Physical activity interventions can prevent depression by improving CRF levels. • This study uses national survey data to explore CRF's mediating role in depression.