The Relationship Between Insomnia and Major Depressive Disorder: a Chicken and Egg Situation

Abstract

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