1. In this systematic review and meta-analysis, it was found that insomnia, hypersomnia, obstructive sleep apnea, and restless legs syndrome acted as risk factors for future depression.
2. Furthermore, both short sleep duration (less than 7 hours) and long sleep duration (more than 8 to 9 hours) had a significant risk for the incidence of depression.
Evidence Rating Level: 1 (Excellent)
Depressive disorders are chronic diseases that often are associated with sleep disorders such as insomnia. Insomnia has been well documented as a risk factor for future incidence of depression; however, there is limited research in other sleep disorders and sleep duration. This study looked at determining if there is a sequential relationship between sleep disorders, circadian disorders, and depression.
This systematic review and meta-analysis was performed under PRISMA guidelines. A literature search of sleep problem terms and depression terms was conducted, with no research participant type or time limitations. Eligible studies were included if they were longitudinal cohort studies, had a minimum 12-month follow-up, excluded participants with baseline depression, and provided outcome indicators. Risk of bias was assessed by the Newcastle-Ottawa scale. Studies which provided depression as a continuous variable, or were case-control or cross-sectional studies were excluded.
Of 12,461 identified records, 56 studies were included in the meta-analysis. Results demonstrated that in the context of a baseline sleep disorder, participants were at a higher risk of depression. Furthermore, the prevalence of insomnia increased with age, but this relationship was not found in depression. Interestingly, three studies used objective sleep measures such as wrist actigraphy and polysomnography to study sleep disorder. These studies found that long sleep duration was the only sleep problem with significant predictive value for future depression. However, one limitation of the systematic review and meta-analysis was that the onset of depression was the only primary outcome, considering that depression is dynamic amongst individuals. Depression may also be a risk factor for sleep disorders; therefore, reverse predictive association would better elucidate the sequential relationship. Nonetheless, this study was a comprehensive evaluation of sleep disorders and their potential as a risk factor for depression.
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