Vulnerability to bipolar disorder is linked to sleep and sleepiness

Abstract

Sleep impairments are a hallmark of acute bipolar disorder (BD) episodes and are present even in the euthymic state. Studying healthy subjects who are vulnerable to BD can improve our understanding of whether sleep impairment is a predisposing factor. Therefore, we investigated whether vulnerability to BD, dimensionally assessed by the hypomanic personality scale (HPS), is associated with sleep disturbances in healthy subjects. We analyzed participants from a population-based cohort who had completed the HPS and had either a 7-day actigraphy recording or a Pittsburgh sleep quality index (PSQI) assessment. In addition, subjects had to be free of confounding diseases or medications. This resulted in 771 subjects for actigraphy and 1766 for PSQI analyses. We found strong evidence that higher HPS scores are associated with greater intraindividual sleep variability, more disturbed sleep and more daytime sleepiness. In addition, factor analyses revealed that core hypomanic features were especially associated with self-reported sleep impairments. Results support the assumption of disturbed sleep as a possibly predisposing factor for BD and suggest sleep improvement as a potential early prevention target.

Fig. 1. Permutation-based quantile–quantile plot showing that the observed p values (blue circles) considerably differ from a random distribution under the null hypothesis (solid diagonal line).

For the set of 84 observed p values (21 sleep variables × 4 personality scores), one million sets of 84 expected p values were derived after data permutation. During data permutation, original correlations within the domain of hypomanic personality variables and the domain of sleep variables were preserved while original correlations between the two domains were removed through random shuffling. Each set of p values was sorted in descending order. The solid diagonal line represents the mean expected p values at rank 1–84 plotted against themselves. The upper and lower bound of the gray area represent the 5th and 95th percentile of expected p values plotted against the mean expected p values. The blue circles represent the observed p values plotted against the mean expected p values

Fig. 2. Boxplots of intraindividual night-to-night variability of actigraphic sleep variables stratified by HPS extreme groups.

Intraindividual night-to-night variability is operationalized by intraindividual standard deviation (ISD) across a single subject’s multiple nights. Boxplots are stratified by top and bottom decile hypomanic personality scale (HPS) groups (HPS+, N = 63 vs. HPS−, N = 61). Boxes represent the interquartile range of each distribution (data between the lower and upper quartile), with the horizontal line corresponding to the median. Whiskers extend to the furthest observation within 1.5 times the interquartile range from the lower and upper quartile. Dots represent single data points, jittered horizontally to avoid overplotting