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Introduction
With 60–80% of individuals with unipolar depression also having insomnia complaints, these two disorders are clearly inter-related (Ohayon, 2002). It is thought that insomnia plays an important role in the development and maintenance of depression complaints. In line with this, cognitive behavioural treatment for insomnia (CBTI) was also found to be efficacious for depressive symptoms (e.g. van der Zweerde et al., 2019). However, it is unclear what treatment components of the CBTI protocol drive these changes. Traditionally, CBT protocols for depression focus mostly on daily functioning and much less on sleep. It stands to reason that the efficacy of depression treatments may be enhanced if specific and brief sleep treatments can be integrated with conventional CBT protocols for depression.
Accordingly, the principal behavioural ingredient of CBTI, which directly targets sleep/bedtimes, appears to be the most promising aspect of CBTI protocols. We hold that sleep restriction therapy (SRT) may be the best, clearly demarcated, candidate treatment component. The goal of SRT is to increase the homeostatic sleep drive by restricting time in bed and strengthening circadian patterning of sleep–wake through regular bedtime and rising time. Importantly, SRT is presumed to be one of the most active treatment components for insomnia (Kyle et al., 2015).
Here, we report on a proof of principle study aimed at evaluating SRT for individuals with both insomnia and depressive complaints. In a first step, and to help prepare for more definitive trial designs in the future, we decided to conduct a case series. We used an AB case series design where participants first completed a waiting-period before the commencement of SRT. We formulated the following hypotheses:
(a) relative to the waiting-period, SRT reduces depressive symptoms and insomnia severity, and improves the sleep diary parameters, and
(b) the presumed beneficial effects of SRT would be maintained at 3- and 6-month follow-up assessments.
Method
For a more complete description of the study method and results, please see the online supplementary material.
Inclusion and exclusion criteria
Inclusion criteria were: (1) 18 years or older, (2) a clinical insomnia diagnosis based on SCID-5-RV, (3) Insomnia Severity Index (ISI) score ≥ 10, (4) sleep efficiency score ≤ 85, (5) Patient Health Questionnaire Depression Scale (PHQ9-D) ≥ 10, (6) Beck Depression Inventory II (BDI-II)...