Sleep variability in delayed sleep-wake phase disorder and insomnia disorder in youth: A case-control study

To compare intraindividual sleep variability in youths with delayed sleep-wake phase disorder (DSWPD) and insomnia disorder (ID), and to examine the association of sleep variability with depressive symptoms and circadian measures. Youths with DSWPD (n = 34, M age = 20.7±1.7, 70.6% female), ID (n = 40, M age = 20.3±2.4, 70.0% female), and healthy sleepers (n = 39, M age = 19.7±2.1, 66.7% female) completed a battery of self-report questionnaires, sleep diary for eight days with actigraphy monitoring, and laboratory-based dim light melatonin onset (DLMO) assessment. Subjective and objective intraindividual variability in sleep parameters were derived from sleep diary and actigraphy data, respectively. Compared with youths with ID, those with DSWPD showed greater variability in diary-derived bedtime ( p = .006), time in bed ( p = .010), and total sleep time ( p = .013). Relative to healthy sleepers, the DSWPD group showed greater variability in diary-derived total sleep time ( p = .017) and actigraphy-derived wake after sleep onset ( p = .040). Both clinical groups showed greater variability in diary-derived sleep onset latency compared with healthy sleepers (DSWPD: p = .011; ID: p < .001). Later DLMO times and higher levels of depressive were significantly associated with increased sleep variability across the full sample. Youths with DSWPD and ID show heightened sleep variability, linked to delayed circadian rhythm and elevated depressive symptoms. Findings highlight the clinical relevance of intraindividual sleep variability. Further prospective and interventional studies are needed to delineate the mechanistic processes associated with increased sleep variabilities in these conditions. • Youths with DSWPD and ID exhibit different patterns of increased subjective and objective sleep variability compared with healthy sleepers. • Based on the subjective measures, both DSWPD and ID groups exhibited greater variability in sleep onset latency versus healthy sleepers, whilst those with DSWPD also showed more irregular sleep duration and sleep schedule than those with ID as measured by sleep diary. • Based on the objective measure, DSWPD group demonstrated greater variability, albeit modest, in wake after sleep onset relative to healthy sleepers. • Later dim light melatonin onset (DLMO) and higher depressive symptoms were associated with greater sleep variability, independent of the clinical status. • Findings suggested the clinical relevance of intraindividual sleep variability in DSWPD and ID. Further longitudinal and interventional research is needed to explore causality and other mechanistic processes associated with increased sleep variability.