The mediating role of depression in the association between disability and quality of life in Alzheimer's disease

Background: An understanding of the determinants of quality of life in Alzheimer's disease (AD) is required in order to develop effective interventions to promote patients' well-being. Most studies have pointed out depression, functional ability and environmental factors. However, unmeasured confounders can jeopardize the interpretation of the results. Objectives: To explore the mediating role of depression in the association between functional status and QoL, and establish a procedure to detect confounding variables. Methods: A sample of 192 AD patients and their respective caregivers were recruited from day centers and health care centers in the region of Murcia (Spain). The mediating effect was evaluated using causal mediation analysis. Covariates were introduced into the model in a stepwise fashion and sensitivity analyses were performed to assess the influence of potential confounders. Results: Self-rated depression acted as a partial mediator between functional status and quality of life. The mediating effect was positive and significant even after including both patient-and caregiver-related covariates. Only if confounders explained more than 80% of the residual variance in the mediator or in the outcome, the mediating effects would not be positive. Conclusions: The effect of lack of autonomy on the QoL is mostly explained by the negative consequences on mood status. The sensitivity analysis confirms the robustness of this finding.