Why Sleep is Key: Poor Sleep Quality is a Mechanism for the Bidirectional Relationship between Major Depressive Disorder and Generalized Anxiety Disorder Across 18 Years
Background: Generalized anxiety disorder (GAD) and major depressive disorder (MDD) reliably precede and predict one another. However, there is insufficient data on mechanisms through which the longitudinal GAD-MDD association unfolds. Based on insomnia theories, such as the hyperarousal model of sleep, we tested the degree to which poor global sleep quality functioned as a mediator of the prospective bidirectional anxiety-depression relationship. Method: Participants were 3,294 community-dwelling adults who partook in 3 waves of measurement spaced 9 years apart. GAD and MDD were assessed in-person using the Composite International Diagnostic Interview-Short Form at baseline (Time 1 [T1]) and 18 years later (T3). T2 global sleep quality was measured using the multiple-domain Pittsburgh Sleep Quality Index self-report at T2. Longitudinal structural equation modeling mediation analysis was used. Results: Analyses showed that higher T1 MDD and GAD severity individually predicted lower T2 global sleep quality (Cohen’s d = -0.570–-0.457), and less T2 global sleep quality thereby forecasted both higher T3 MDD and GAD (d = -0.487–-0.422). Poorer T2 global sleep quality significantly mediated the T1 GAD–T3 MDD relation (controlling for T1 MDD), accounting for 83.93% of the association. Poorer global sleep quality at T2 also significantly mediated the T1 MDD–T3 GAD association (controlling for T1 GAD), accounting for 100% of the relation. Conclusions: Findings offer evidence for transdiagnostic theories of sleep and insomnia. Theoretical and clinical implications, such as the importance of prioritizing sleep improvement in cognitive behavioral therapies, are also discussed.
