Study objectives: Depression has been identified as the most common condition comorbid to insomnia, with findings pointing to the possibility that these disorders may be causally related to each other or may share common mechanisms. Some have suggested that comorbid insomnia and depression may have a different clinical course than either condition alone, and may thus require specific treatment procedures. In this report we examined the clinical characteristics of individuals referred to an academic sleep center who report comorbid symptoms of insomnia and depression and those with symptoms of insomnia outside the context of meaningful depression, and we identified differences between these groups with regard to several cognitive-related variables.
Methods: Logistic regression analyses examined whether past week worry, dysfunctional beliefs about sleep, and insomnia symptom-focused rumination predicted group membership.
Results: Individuals with comorbid symptoms of insomnia and depression reported more past-week worry, dysfunctional beliefs about sleep, and insomnia symptom-focused rumination, than those with symptoms of insomnia without significant depression symptoms. When including all three cognitive-related variables in our model, those with comorbid symptoms reported more severe insomnia symptom-focused rumination, even when controlling for insomnia and mental health severity, among other relevant covariates.
Conclusion: The findings contribute to our understanding of the complex nature of comorbid symptoms of insomnia and depression and the specific symptom burden experienced by those with significant depression symptoms in the presence of insomnia. The findings also highlight the need for increased clinical attention to the sleep-focused rumination reported by these patients.
Keywords: cognition; depression; insomnia; mood; rumination; sleep; worry.
© 2015 American Academy of Sleep Medicine.