Sleep disturbances and depression: risk relationships for subsequent depression and therapeutic implications.

The majority of individuals with depression experience sleep disturbances. Depression is also over-represented among populations with a variety of sleep disorders. Although sleep disturbances are typical features of depression, such symptoms sometimes appear prior to an episode of depression. The bidirectional associations between sleep disturbance (especially insomnia) and depression increase the difficulty of differentiating cause-and-effect relationships between them. Longitudinal studies have consistently identified insomnia as a risk factor for the development of a new-onset or recurrent depression, and this association has been identified in young, middle-aged, and older adults. Studies have also observed that the combination of insomnia and depression influences the trajectory of depression, increasing episode severity and duration as well as relapse rates. Fortunately, recent studies have demonstrated that both pharmacological and nonpharmacological interventions for insomnia may favorably reduce and possibly prevent depression. Together, these findings suggest that sleep-related symptoms that are present before, during, andlor after a depressive episode are potentially modifiable factors that may play an important role in achieving and maintaining depression remission.