Report from a randomized control trial: improved alignment between circadian biology and sleep–wake behavior as a mechanism of depression symptom improvement in evening‐type adolescents with depressive symptoms

Study objectives An evening circadian preference is common among adolescents. It is characterized by a behavioral predilection for later sleep and wake timing and is associated with higher rates of Major Depressive Disorder (MDD). The present study aims to (a) test the effectiveness of a cognitive behavioral sleep intervention (Transdiagnostic Sleep and Circadian Intervention; TranS‐C) in a sample of adolescents with an evening circadian preference and clinically significant depressive symptoms and (b) evaluate improved alignment between circadian biology and sleep–wake behavior as a potential mechanism in the relationship between sleep and depression symptom improvement. Methods Adolescents with an evening circadian preference and clinically significant depressive symptoms were randomized to receive TranS‐C ( n = 24) or a psychoeducation condition (PE; n = 18). Alignment between circadian biology and sleep–wake behavior was measured using objective biological measurement. Measures of sleep and circadian rhythm were taken at pre‐ and posttreatment, and depression symptoms were measured at pre‐ and posttreatment and 6‐ and 12‐month follow‐up. Results Mixed effects modeling revealed that compared with an active control condition, TranS‐C resulted in a significant reduction in MDD severity at 12‐month follow‐up. A MacArthur mediation analysis conducted to explore alignment between circadian biology and sleep–wake behavior as a mediator of depression severity reduction through 12‐month follow‐up revealed a significant interaction between change in alignment between circadian biology and sleep–wake behavior and treatment arm, indicating that improved alignment between circadian biology and sleep–wake behavior at posttreatment was associated with improvements in depression outcomes at 12‐month follow‐up under the treatment condition. Conclusions These results provide novel evidence for improved alignment between circadian biology and sleep–wake behavior as a specific mechanism of depression improvement, provide key clues into the complex relationship between sleep and depression, and have significant clinical implications for adolescents with depression.