Published online by Cambridge University Press: 14 June 2018
Background: Recent treatment studies with cognitive behavioural therapy for insomnia (CBT-I) have demonstrated effects on both sleep problems and depression. Two previous studies have indicated that the beneficial effect from CBT-I on depression may come through improved sleep, although insomnia severity during treatment had not previously been investigated as a mediator. Aims: Our aim was to investigate if insomnia severity during treatment mediated between CBT-I and depression severity after treatment, in a sample with co-morbid insomnia and depressive symptomology. We also examined whether depressive severity during treatment mediated between CBT-I and insomnia after treatment. Method: The participants were recruited from advertisements and fulfilled criteria for insomnia diagnosis, and had depressive symptomatology (Beck Depression Inventory-second edition: BDI-II > 13). Two-thirds of the participants were diagnosed with major depressive disorder. The participants received four biweekly group sessions of CBT-I or relaxation training (active control). Insomnia severity (Insomnia Severity Index) and depressive severity (BDI-II) were measured at baseline, mid-treatment, post-treatment and 6-month follow-up. The mid-treatment measures were used as mediators. Results: Mediational analyses demonstrated a significant reciprocal relationship between insomnia severity and depressive severity throughout CBT-I, although mid-treatment insomnia had a stronger effect on depression than mid-treatment depression had on insomnia. The results were similar for both post-treatment and follow-up. Discussion: Some improvement in depressive severity after CBT-I is explained by improved sleep. The findings emphasize the importance of making comorbid insomnia a treatment focus in its own right.
Some of the data have been presented as an oral poster at the 46th European Association of Behavioural and Cognitive Therapies congress, 31 August–3 September 2016, Stockholm, Sweden.
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