Rationale: Alzheimer’s disease caregivers demonstrate significant elevations in depression compared with noncaregivers. Addressing caregiver depression is of high public health importance due to its ties with overall wellbeing, increased risk for cardiovascular diseases (CVD), and ability to sustain caregiving duties. Improving caregiver mental and physical health may not only decrease healthcare costs, but it may also delay institutionalization of Alzheimer’s disease patients. Despite existing behavioral interventions to address caregiver depression and physical health issues, little is known regarding which interventions to recommend based on individual caregiving situations. To improve the impact of caregiver interventions, it is essential to understand the mechanisms through which interventions achieve reductions in depression and CVD risk, as well as the caregiving situation-related factors that may impact response to interventions.
Design: The proposed study employs a data analytic focus on mediators and moderators of a previously completed randomized clinical trial testing the efficacy of the Pleasant Events Program (PEP). A sample of spousal Alzheimer’s Disease caregivers (N = 100; 74% female) was randomized to receive either a Behavioral Activation therapy, named the Pleasant Events Program (PEP), or to a time-equivalent Informational Support control condition (n = 51). The PEP intervention emphasized pleasant events scheduling and reductions in avoidance behaviors (i.e., lack of engagement in activities) in the context of ongoing caregiver responsibilities, whereas the Informational Support intervention emphasized supportive listening and providing information. Participants were assessed at baseline and at 6-weeks (i.e., post-intervention). Co-primary outcomes were CVD risk marker interleukin-6 and depression as measured by the Center for Epidemiologic Studies-Depression Scale. Higher levels of interleukin-6 are implicated in inflammatory processes, constituting higher risk for CVD. The PEP efficacy study reported significant reductions in both depression and interleukin-6 at 6-weeks follow-up. Multiple regression models and the Monte Carlo Method for Assessing Mediation were used to test change in pleasant events, activity restriction, and personal mastery as mediators of depression after PEP. Moreover, depression was tested as a mediator between PEP and reductions in CVD risk markers interleukin-6. Secondly, models were used to investigate constructs measured via standardized assessments (e.g., care recipient disruptive behaviors) as moderators of PEP outcomes.
Results & Conclusions: The current study found that change in personal mastery, activity restriction, and pleasant activities were not significant mediators of change in depression after PEP. Moreover, changes in depression did not mediate changes in cardiovascular risk marker interleukin-6. Caregiver social support, current number of hours working, vulnerability, and disruptive behaviors of care recipients did not significantly moderate treatment response. Higher baseline depression significantly predicted greater reduction in depression in both treatment conditions. The current study was limited in power to detect mediators and moderators of depression and CVD risk change after PEP. Potential caregiver-specific factors that may moderate response to PEP and mediators that account for changes in depression and CVD risk after PEP are still unknown. Thus, future intervention studies utilizing a Behavioral Activation therapy such as PEP should utilize oversampling methods to investigate mediators and moderators of depression and interleukin-6 change.