Results provide evidence that the wide dissemination of dCBT-I may effectively target both insomnia and comorbid depression across a wide spectrum of the population.

Study Objectives Insomnia is a common precursor to depression; yet, the potential for insomnia treatment to prevent depression has not been demonstrated. Cognitive behavioral therapy for insomnia (CBT-I) effectively reduces concurrent symptoms of insomnia and depression and can be delivered digitally (dCBT-I); however, it remains unclear whether treating insomnia leads to sustained reduction and prevention of depression. This randomized controlled trial examined the efficacy of dCBT-I in reducing and preventing depression over a 1-year follow-up period. Methods Patients with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) insomnia disorder were randomly assigned to receive dCBT-I or an attentional control. The follow-up sample included 358 patients in the dCBT-I condition and 300 patients in the online sleep education condition. The primary outcome measure was relative rate ratios for depression at 1-year follow-up. Insomnia responses to treatment were also tested as predictors of incident depression at the 1-year follow-up. Results At 1-year follow-up, depression severity continued to be significantly lower in the dCBT-I condition relative to control. In addition, the number of individuals who reported no depression at 1-year follow-up was 51% higher in the dCBT-I condition relative to control. In those with minimal to no depression at baseline, the incident rate of moderate-to-severe depression at 1-year follow-up was reduced by half in the dCBT-I condition relative to the control condition. Conclusion dCBT-I showed robust effects as an intervention that prevents depression. Future research should examine dose–response requirements and further characterize mechanisms of action of dCBT-I for depression prevention. Clinical Trial Sleep to Prevent Evolving Affective Disorders; NCT02988375.

Deficits in cognitive functioning associated with shift work are particularly relevant to occupational performance; however, few studies have examined how cognitive functioning is associated with specific components of shift work. This observational study examined how circadian phase, nocturnal sleepiness, and daytime insomnia in a sample of shift workers ( N = 30) were associated with cognitive flexibility during the night shift. Cognitive flexibility was measured using a computerized task-switching paradigm, which produces 2 indexes of flexibility: switch cost and set inhibition. Switch cost represents the additional cognitive effort required in switching to a different task and can impact performance when multitasking is involved. Set inhibition is the efficiency in returning to previously completed tasks and represents the degree of cognitive perseveration, which can lead to reduced accuracy. Circadian phase was measured via melatonin assays, nocturnal sleepiness was assessed using the Multiple Sleep Latency Test, and daytime insomnia was assessed using the Insomnia Severity Index. Results indicated that those with an earlier circadian phase, insomnia, and sleepiness exhibited reduced cognitive flexibility; however, specific components of cognitive flexibility were differentially associated with circadian phase, insomnia, and sleepiness. Individuals with an earlier circadian phase (thus more misaligned to the night shift) exhibited larger switch costs, which was also associated with reduced task efficiency. Shift workers with more daytime insomnia demonstrated difficulties with cognitive inhibition, whereas nocturnal sleepiness was associated with difficulties in reactivating previous tasks. Deficits in set inhibition were also related to reduced accuracy and increased perseverative errors. Together, this study indicates that task performance deficits in shift work are complex and are variably impacted by different mechanisms. Future research may examine phenotypic differences in shift work and the associated consequences. Results also suggest that fatigue risk management strategies may benefit from increased scope and specificity in assessment of sleep, sleepiness, and circadian rhythms in shift workers.

This study provides further evidence for multiple mechanisms (ie, circadian misalignment versus sleep reactivity to stress) associated with daytime sleep disturbances in shift workers. Additionally, it provides the new finding that genotype may play an important role in individual vulnerability to the different mechanisms of daytime sleep disturbance in night shift workers.

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