Social jetlag, a form of circadian misalignment, has been suggested to induce several clinical symptoms such as mental/physical health problems. However, evidence on the association of social jetlag with general daytime functioning (e.g., school life) is limited. This cross-sectional study aimed to 1) estimate the distribution of social jetlag exceeding one hour and 2) comprehensively explore the associations between social jetlag and irritable mood, daytime sleepiness, and poor academic performance among Japanese adolescents. The study included 4,782 students aged 12-15 years, from 13 junior high schools, who completed a self-administered questionnaire. Social jetlag was calculated as the difference in the midpoint of sleep between weekdays and weekends and was categorized as follow: negative, <1 h, 1-2 h, or ≥2 h. Outcomes were irritable mood, daytime sleepiness, and academic performance, which were analyzed with generalized linear mixed models to examine the relations with social jetlag, with adjustments for potential confounders like sleep quality. The distribution of social jetlag of ≥1 h was 51.1%, including 1-2 h (35.8%) and ≥2 h (15.3%). Its most frequently observed duration was 0 to <1 h (41.0%), followed by negative social jetlag (7.9%). The full adjusted model revealed that social jetlag of ≥1 h was associated with elevated risk of irritable mood, daytime sleepiness, and poor academic performance, while negative social jetlag was associated only with poor academic performance. Social jetlag was highly prevalent among Japanese adolescents and could be a major risk factor for irritable mood, daytime sleepiness, and poor academic performance.BMI, Body mass index; DLMO, Dim light melatonin onset; CIs, Confidence intervals; MSF, The midpoints of sleep on free days; MSF, Sleep-corrected MSF; MSW, The midpoints of sleep on weekdays; PDSS, The Pediatric Daytime Sleepiness Scale. Abbreviations: sc
