Depression and anxiety escalate across academic semesters within a dominant annual rhythm: Weekly multiyear evidence...

Depressive and anxiety symptoms among university students fluctuate across the academic year, but their temporal structure remains unclear. Explanations emphasize semester-related academic stress, seasonal rhythms, or their combination. This study examined whether symptoms follow semester-length cycles, annual cycles, or an integrated structure.

Weekly depressive (PHQ-9) and anxiety (GAD-7) scores were drawn from seven academic years (2018-2025) of the Healthy Minds Study (242 weeks; N = 651,559). Generalized least squares models with first-order autoregressive errors were estimated, and sequential model comparisons evaluated secular trend and semester fixed effects, 26-week harmonic terms, 52-week harmonic terms, quadratic week-of-semester progression, and a combined annual and intra-semester specification.

First, 52-week harmonic terms accounted for more variance and produced a greater reduction in residual autocorrelation than semester-length oscillation. Second, symptom amplitude was asymmetric across terms, with a larger peak-to-trough swing in fall than in spring. Third, symptoms did not fully reset between terms, declining modestly across the inter-semester interval. Within-semester escalation remained significant after accounting for annual periodicity, indicating that academic progression operated within the broader annual rhythm. Symptoms peaked around Weeks 11-12 in fall and Weeks 13-15 in spring.

Student mental health is best understood as a layered temporal system in which intra-semester escalation is embedded within a dominant annual rhythm. Recognizing this structure may help universities align screening, prevention, and support with predictable, year-spanning vulnerability, not just isolated examination periods.