The toll of an early bell: school start time and adolescent sleep quality in Flanders

Abstract Background Adolescent sleep health is a growing public health concern, with poor sleep linked to adverse mental and physical health. Early school start times often conflict with adolescents’ naturally delayed sleep rhythms during puberty, contributing to poor sleep quality. While international evidence suggests that later school start times improve sleep outcomes, this relationship is underexplored in Flanders. This study examines the association between school start time and adolescent sleep quality in Flemish secondary schools. Methods Data were drawn from the 2022 Flemish Health Behaviour in School-aged Children (HBSC) survey, including 16,253 adolescents (mean age = 15.46, SD = 1.85) from 103 secondary schools. Sleep quality was assessed using the Groningen Sleep Quality Scale (α = .90), with five items on poor sleep, difficulty falling asleep, insufficient sleep, disturbed sleep and morning fatigue. Participants rated the frequency of these issues (never = 1 to always = 5) and a total score was calculated. School start time data (hours and minutes) were collected. Linear regression analyses assessed the association between school start time and sleep quality. Analyses were controlled for covariates selected based on Directed Acyclic Graphs. Results Later school start times were associated with better sleep quality. Specifically, each additional minute of delay in school start time was associated with a decrease of 0.022 in the sleep quality score (β = -0.022, p < .001), suggesting a modest improvement in sleep quality with later school start times. Conclusions These findings suggest that later school start times are linked to higher sleep quality among adolescents in Flanders. Aligning school schedules with adolescents’ natural sleep rhythms could serve as an effective public health intervention to mitigate poor sleep and its related consequences. Key messages • Later school start times are linked to improved sleep quality in adolescents. • Delaying school start times to align with adolescents’ natural sleep rhythms can improve sleep health, offering a promising direction for public health policy.