Variation in sleep and instability in mood in patients with bipolar disorder and the association between these – an exploratory post hoc study on daily smartphone-based data from two separate randomised controlled trials

Background Dysregulation in circadian rhythms, including sleep abnormalities, is a central feature in bipolar disorder during all illness phases. This exploratory post hoc study investigated the association between variation in sleep and instability in mood based on day-to-day patient-reported smartphone-based data in patients with bipolar disorder. Methods Data from patients with bipolar disorder from two prior studies (A-Bipolar and SMART-Bipolar) were included for exploratory analyses. Patients provided daily smartphone-based evaluations of sleep and mood. A total of 370 patients with bipolar disorder each providing data for six months were included in the analyses. We analysed how various summaries of sleep variation were associated with mood instability, using linear mixed effect regression models. Results There was a positive association between variation in sleep for both the prior three days (1.22, 95%CI: (1.19; 1.24), p < 0.0001) as well as the prior week (1.40,95% CI: (1.36, 1.44), p < 0.0001)) and mood instability. Interestingly, increasing sleep up to a certain point around eight hours was associated with decreased mood instability. Increasing sleep after this point was associated with increased mood instability. The estimated inflection point for this choice of knots was 8.05 h (95% CI: 7.20,8.90) for the A-bipolar study and 8.24 h (95% CI: 6.24,10.24) for SMART-Bipolar study. Limitations Analyses were exploratory and post hoc. Sleep and mood were patient-reported. Findings should be interpreted with caution. Temporal ordering of the associations cannot be concluded. Conclusion In this exploratory study of patients with bipolar disorder, short-term fluctuations in sleep were significantly associated with increased mood instability, highlighting the dynamic interplay between circadian regulation and affective variability.