The effect of psychotherapy on the multivariate association between insomnia and depressive symptoms in late-life depression

Background: Late-life depression (LLD) is prevalent in older adults and linked to increased disability, mortality, and suicide risk. Insomnia symptoms are considered common remaining symptoms of LLD following treatment. However, the multivariate relationship between insomnia and depressive symptoms and the impact of psychotherapy on their interrelationship is insufficiently assessed. Methods: We used data from 185 patients with LLD recruited from seven university hospitals in Germany. Participants had undergone eight-week psychotherapy interventions (cognitive behavioral therapy or supportive unspecific intervention). Three regularized canonical correlation analyses (rCCA) assessed the multivariate association between insomnia and depressive symptoms at baseline, post-treatment, and six-month follow-up. rCCA was conducted within a machine learning framework with 100 repeated hold-out splits and permutation tests to ensure robust findings. Canonical loadings and cross-loading difference scores were calculated to examine symptom changes before/after psychotherapy (Holm-Bonferroni corrected p-value < 0.05). Results: At baseline, a moderate association was observed between insomnia and depressive symptoms (r = 0.24). Interestingly, this association slightly increased after the eight-week treatment period (r = 0.42, pcorrected = 0.064) and remained significantly elevated at the follow-up session (r = 0.49, pcorrected = 0.018). At baseline, anxiety-related depressive symptoms were mainly associated with insomnia, while at post-treatment and follow-up sessions, somatic and negative affective symptoms showed the strongest correlation with insomnia symptoms. Although depressive symptoms significantly improved, insomnia symptoms remained unchanged after psychotherapy. Conclusions: Unlike depressive symptoms, insomnia symptoms did not improve after psychotherapy, highlighting the necessity to target insomnia for effective LLD treatment.