0461 Evaluating the Relationship Between Rumination and Insomnia Across CBTI in Depressed Adults

Abstract Introduction Previous work suggests that ruminative thoughts, even when not sleep-related, are associated with more severe insomnia symptoms. However, few studies have examined whether interventions that target insomnia may also improve rumination over time. It remains untested whether improvements in insomnia severity resulting from CBTI are driving improvements in rumination. Likewise, it is unknown whether the link between higher rumination and insomnia is present at all assessed timepoints. Here we conducted a secondary analysis of a previous single-arm mechanistic CBTI trial (NCT04424407) to test the hypotheses that (1) CBTI would be associated with improvements in rumination, (2) improvements in rumination would be associated with improvements in insomnia, and (3) that these associations would persist after treatment. Methods Fifty individuals (age mean+/-SD = 40.36+/-10.95 years; 64% female; 48 completers), with co-occurring insomnia and depressive symptoms completed the insomnia severity index (ISI) and Ruminative Responses Scale-Short (RRS) before and after receiving 6-sessions of CBTI. Linear mixed effects models tested the impact of CBTI on rumination, longitudinal associations between ISI and RRS, and whether treatment moderated these associations. Linear regression tested associations between symptoms changes. Age and sex were included as covariates in all models. Results CBTI was associated with an improvement in rumination (b=-2.65, p=0.002) following treatment. Improvements in insomnia symptoms were not associated with changes in rumination (b=-0.04, p=0.85). Rumination and insomnia were not associated with each other overtime (b=0.05, p=0.74). Moderation analyses revealed that the associations were not different across timepoints (b=0.03, p=0.90): ISI and RRS were not associated at baseline nor post-treatment (|b’s| 0.07, p’s0.70). Conclusion CBTI was associated with improvement in rumination at post-treatment. However, counter to our hypotheses, insomnia and rumination symptoms were not associated. Limited variability in insomnia and rumination scores in our sample may be occluding our expected effects (i.e. all participants had insomnia/depression at study entry). These findings indicate that improvements in rumination following CBTI may not be due to changes in insomnia itself. Future studies should examine whether subcomponents of rumination, mood variability, or broader sleep health shape these relationships. Support (if any) R61MH120245 and R33MH120245