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

OBJECTIVES: 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. METHODS: Youths with DSWPD (n = 34, Mage = 20.7 ± 1.7, 70.6% female), ID (n = 40, Mage = 20.3 ± 2.4, 70.0% female) and healthy sleepers (n = 39, Mage = 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. RESULTS: 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 symptoms were significantly associated with increased sleep variability across the full sample. CONCLUSIONS: 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 variability in these conditions.