The relationship between generalized anxiety disorder (GAD) and major depressive disorder (MDD) may be mediated by sleep and insomnia factors. These findings were published in the Journal of Anxiety Disorders.
Community-dwelling adults (N=3294) were recruited in 1995 and 1996 for the Midlife Development in the United States (MIDUS) project. Participants were evaluated for MDD, GAD, and global sleep quality at time 1 (T1; 1995-1996), time 2 (T2; 2004-2005), and time 3 (T3; 2013-2014).
MDD and GAD were assessed using the Diagnostic and Statistical Manual–Third Edition–Revised (DSM-III-R) and the aligned Composite International Diagnostic Interview–Short Form (CIDI-SF). Sleep quality was assessed using the 19-item Pittsburgh Sleep Quality Index (PSQI). These data were evaluated using a mediation analysis approach.
At baseline, the study population consisted of 54.61% women, aged mean 45.62 years (range, 20-74) years. A total of 92.93% were White.
The first hypothesis was the GAD at T1 led to MDD at T3 mediated by sleep quality at T2. This model had a good fit (χ2, 1080.834; P <.001), indicating that increased GAD symptom severity at T1 predicted global sleep quality at T2 (β, -0.078; P <.001) and poorer global sleep quality at T2 predicted increased MDD severity at T3 (β, -0.183; P <.001). Altogether, 41.340% of the relationship between T1 GAD and T3 MDD was mediated by T2 global sleep quality.
The second hypothesis was the MDD at T1 led to GAD at T3 mediated by sleep quality at T2. This model had a good fit (χ2, 625.192; P <.001), indicating that increased MDD symptom severity at T1 predicted global sleep quality at T2 (β, -0.606; P <.001) and poorer global sleep quality at T2 predicted increased GAD severity at T3 (β, -0.214; P =.050). Altogether, 10.819% of the relationship between T1 MDD and T3 GAD was mediated by T2 global sleep quality.
Indirect effects from both hypotheses remained significant after controlling for age, gender, past-year chronic sleep problems, number of comorbidities, number of medications, level of physical activity, total household income, and current financial situation.
The major limitation of this study was that objective sleep measures were not evaluated.
The study authors concluded, “Our findings further refine the longitudinal between-subject relationship between MDD and GAD across 18 years. Global subjective sleep quality at T2 mediated the T1 MDD–T3 GAD relation and vice versa. Future studies should consider utilizing objective measures of sleep quality and DSM-5 measures and recruiting culturally diverse samples.”
Nguyen VV, Zainal NH, Newman MG. 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. J Anxiety Disord. 2022;90:102601. doi:10.1016/j.janxdis.2022.102601