Temporal dynamics of subjective sleep profiles predicting mood improvements during adjunctive light therapy combined with sleep rescheduling

Abstract

• Sleep-enhancement following light therapy may contribute to rapid mood improvements. • Subsequent alleviation of sleep-related daytime dysfunction may further improve mood. • Self-reported sleep variables may predict antidepressant response to light therapy. Light therapy yields inconsistent results in people with non-seasonal depression, which may in part be due to heterogeneous responses and the temporal dynamics of changes in sleep, daytime functioning and mood. This study assessed the timeline of the antidepressant effects of light therapy and sleep rescheduling relative to changes in sleep and daytime sleep-related factors, and sought to identify predictors of treatment response in young people with depression. Twenty-four individuals with depression (mean±SD: 21.2±1.0 years old;17% male) underwent adjunctive morning light therapy with a wake-up phase advance over four weeks. They completed the Beck Depression Inventory-II (BDI-II) and Leeds Sleep Evaluation Questionnaire. On average, BDI-II scores decreased significantly after four weeks of intervention ( F (2,32)=3.5, p =.044, ηp 2 =0.18). After two weeks, improvements in the ease of getting to sleep and sleep quality were significantly associated with BDI-II improvements ( F (2,21)=6.3, p =.007). From two to four weeks, improvements in daytime sleep-related factors were significantly associated with BDI-II improvements ( F (2,12)=6.0, p =.015). More sleep-related difficulties prior to the intervention tended to predict BDI-II improvements across the four weeks of light therapy ( F (2,14)=3.7, p =.053). Open-label design and small sample size. Sleep-enhancement emerging in the early phase of light therapy and sleep rescheduling may subsequently alleviate sleep-related daytime dysfunctions, which may in turn further improve mood. Controlled trials are required to confirm whether the antidepressant effects of light may be linked to the attenuation of sleep-related difficulties, and whether sleep difficulties may be useful predictors of the antidepressant response to light therapy.