Circadian clock adjusted classes improve sleep, circadian health, and academic performance in medical freshmen

University students often experience circadian misalignment with academic schedules, which may impair performance. This study evaluated whether a later-start schedule improves academic outcomes and circadian rhythms in first-year medical students. Incoming students (n = 220) completed the Munich Chronotype Questionnaire; those with high social jetlag (SJL >120 min, n = 71) were randomized into either a later-start schedule (LS; classes ≥10:00 a.m., n = 30) or a standard early-start schedule (ES; 8:00 a.m., n = 41). Actigraphy data were collected from 112 students prior to examinations. Based on the objective temperature circadian phase (TCP) with a median acrophase split at 3:59 a.m. ES participants were categorized asearly (ETCP-ES, n = 41) or late (LTCP-ES, n = 41). All LS participants exhibited a TCP later than 3:59 a.m. and remained LTCP-LS group (n = 30). Associations between scheduling, circadian metrics, and exam scores were analyzed using regression and sex-adjusted ANCOVA. TCP predicted exam scores overall (β = -0.217, p = 0.021), most evidently within ES (β = -0.291, p = 0.008). LTCP-ES students scored lower than ETCP-ES students (p = 0.025). LTCP-LS students performed similarly to ETCP-ES students and showed greater circadian robustness, including higher rest-activity stability (p = 0.031), greater blue-light stability (p = 0.029), and longer sleep duration (p = 0.013).