Research paperSubjective versus objective evening chronotypes in bipolar disorder

- Chronotype measured in 61 BD subjects and 61 controls via self-report and actigraphy.
- BD subjects showed more evening chronotype than controls using both measures.
- Self-report and actigraphy chronotype correlated within groups and across full sample.
- 21 nights of actigraphy correctly identified evening chronotype in ≥ 95% of subjects.

BackgroundDisturbed sleep timing is common in bipolar disorder (BD). However, most research is based upon self-reports. We examined relationships between subjective versus objective assessments of sleep timing in BD patients versus controls.MethodsWe studied 61 individuals with bipolar I or II disorder and 61 healthy controls. Structured clinical interviews assessed psychiatric diagnoses, and clinician-administered scales assessed current mood symptom severity. For subjective chronotype, we used the Composite Scale of Morningness (CSM) questionnaire, using original and modified (1, ¾, ⅔, and ½ SD below mean CSM score) thresholds to define evening chronotype. Objective chronotype was calculated as the percentage of nights (50%, 66.7%, 75%, or 90% of all nights) with sleep interval midpoints at or before (non-evening chronotype) vs. after (evening chronotype) 04:15:00 (4:15:00 a.m.), based on 25-50 days of continuous actigraph data.ResultsBD participants and controls differed significantly with respect to CSM mean scores and CSM evening chronotypes using modified, but not original, thresholds. Groups also differed significantly with respect to chronotype based on sleep interval midpoint means, and based on the threshold of 75% of sleep intervals with midpoints after 04:15:00. Subjective and objective chronotypes correlated significantly with one another. Twenty-one consecutive intervals were needed to yield an evening chronotype classification match of ≥ 95% with that made using the 75% of sleep intervals threshold.LimitationsLimited sample size/generalizability.ConclusionsSubjective and objective chronotype measurements were correlated with one another in participants with BD. Using population-specific thresholds, participants with BD had a later chronotype than controls.