Actigraphic assessment of delayed sleep–wake rhythm could predict functional impairment in patients with bipolar disorder: A cross-sectional study

Background: Delayed sleep–wake rhythm is a common but often under-recognized feature in patients with bipolar disorder (BD). This study aimed to investigate the association between a delayed sleep–wake rhythm and functional impairment using actigraphy. Methods: Participants with BD in clinical remission (N = 47) were recruited. Sleep parameters, including the midpoint of sleep (o’clock), total sleep time (min), sleep efficiency (%), and wake after sleep onset (min), were averaged over 14 days of continuous actigraphy. Functional impairment was assessed using the 12-item World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0). Correlation analyses were performed to examine the relationships between the total WHODAS 2.0 scores and sleep parameters. Multiple regression analyses were conducted using WHODAS 2.0 scores, with total scores as the dependent variable and sleep parameters as independent variables, controlling for mood and insomnia severity. Results: In the correlation analysis, a significant positive relationship was found between the midpoint of sleep and total WHODAS 2.0 scores ( r = 0.424, p = 0.003). Multiple regression analysis identified the midpoint of sleep as a significant predictor of total WHODAS 2.0 scores ( β = 0.419, p = 0.007). Conclusion: Delayed sleep-wake rhythms may affect functional impairment in patients with BD during the euthymic phase. This suggests that advancing the sleep–wake rhythm may contribute to improvements in social functioning. Actigraphy can potentially be a digital biomarker for assessing functional impairment.