The impact of biological rhythms and sleep quality on the link between depression and functionality in bipolar disorder.

This study examined the role of biological rhythms and sleep quality on the impact of depression on functionality in bipolar disorder (BD) and compared these factors between euthymic bipolar patients and healthy controls. Ninety-eight patients with BD were included in the study and recategorized as euthymic or depressive based on their Hamilton Depression Rating Scale scores, along with ninety-six healthy controls. Biological rhythms, functionality, and sleep quality were evaluated utilizing the Biological Rhythms Assessment in Neuropsychiatry, Functioning Assessment Short Test, and Pittsburgh Sleep Quality Index. Biological rhythms and sleep were more disrupted in bipolar depression, with no differences between euthymic patients and controls. Positive correlations were found among depression, functionality, sleep quality, and biological rhythms. Mediation analysis revealed that biological rhythm disturbances partially mediate the link between depression and functionality, while sleep quality does not. Interventions addressing both depression and biological rhythms may improve functionality in BD.