Depression and insomnia as mediators of the relationship between distress and quality of life in cancer patients

Background: Distress in cancer patients leads to poorer quality of life (QOL) and negatively impacts survival. For efficient management of a patient's disease course, the interrelationships among distress, depression, insomnia, and QOL must be understood. This study aimed to investigate whether depression and insomnia mediate the relationship between distress and QOL in cancer patients. Methods: Cancer patients referred to a specialized psycho-oncology clinic (n = 208) participated in this study. Distress, depression, insomnia, and QOL were measured with the following questionnaires: Distress Thermometer, Hospital Anxiety and Depression Scale, Insomnia Severity Index, and Functional Assessment of Cancer Therapy-General. Structural equation modeling and path analysis were performed to analyze the mediating effects of depression and insomnia on the relationship between distress and QOL. Results: Distress exerted nearly equal direct (beta=-0.291, p = 0.002) and indirect (mediated by depression and insomnia) (beta= 0.299, p=0.003) negative effects on QOL. Depression exhibited the largest direct negative effect on QOL. The indirect effects of distress on QOL through depression alone, through insomnia alone, and through an insomnia to depression pathway were all significant (beta= 0.122, p=0.011; beta=0.102, p=0.002; and beta=0.075, p < 0.001, respectively). Limitations: The cross-sectional analyses limit the measurement of causal relationships between each variable. Conclusions: Depression and insomnia, both individually and as part of an interrelated pathway, partially mediate the relationship between distress and QOL. Appropriate interventions to alleviate insomnia and depression may mitigate the negative impacts of distress on QOL in cancer patients.