Schools are central places for adolescent social lives, which is a major factor greatly affecting adolescent mental health; school climate (i.e. quality of the school social environments) can be a proximal social determinant for adolescent mental health. Supportive school environments may serve as a protective factor during crises like COVID-19, which disrupt social lives and worsen adolescent mental health. This is the first study examining whether the pandemic effects differed based on the levels of school climate on depressive symptoms (DS) and psychotic experiences (PEs) among adolescents.

School climate (score range: 0–28), DS (0–26), and PEs (0–5) were self-reported in a population-based cohort (Tokyo Teen Cohort; N = 3171) at four timepoints (10y, 12y, 14y, and 16y) before and during COVID-19. COVID-19 occurred midway through the 16y survey, allowing us to examine its impact and interaction effect with school climate while accounting for within-person changes over time using mixed-effects models.

Significant interaction effects were found on DS (unstandardized coefficient [B] = −0.166, 95% confidence interval [CI] −0.225 to −0.107) and PEs (B = −0.020, 95% CI −0.028 to −0.012). The pandemic effects were not significant for adolescents with high school climate scores (around the 80th percentile or higher), although the pandemic significantly worsened these outcomes among the overall sample.

The negative mental health effects of the pandemic were significantly mitigated among adolescents experiencing a supportive school climate. A positive school climate can protect adolescent mental health during challenging social conditions, such as pandemics.

Altered white matter brain connectivity has been linked to depression. The aim of this study was to investigate the association of markers of white matter connectivity with prevalence, incidence and course of depressive symptoms.

Markers of white matter connectivity (node degree, clustering coefficient, local efficiency, characteristic path length, and global efficiency) were assessed at baseline by 3 T MRI in the population-based Maastricht Study (n = 4866; mean ± standard deviation age 59.6 ± 8.5 years, 49.0% women; 17 406 person-years of follow-up). Depressive symptoms (9-item Patient Health Questionnaire; PHQ-9) were assessed at baseline and annually over seven years of follow-up. Major depressive disorder (MDD) was assessed with the Mini-International Neuropsychiatric Interview at baseline only. We used negative binominal, logistic and Cox regression analyses, and adjusted for demographic, cardiovascular, and lifestyle risk factors.

A lower global average node degree at baseline was associated with the prevalence and persistence of clinically relevant depressive symptoms [PHQ-9 ⩾ 10; OR (95% confidence interval) per standard deviation = 1.21 (1.05–1.39) and OR = 1.21 (1.02–1.44), respectively], after full adjustment. On the contrary, no associations were found of global average node degree with the MDD at baseline [OR 1.12 (0.94–1.32) nor incidence or remission of clinically relevant depressive symptoms [HR = 1.05 (0.95–1.17) and OR 1.08 (0.83–1.41), respectively]. Other connectivity measures of white matter organization were not associated with depression.

Our findings suggest that fewer white matter connections may contribute to prevalent depressive symptoms and its persistence but not to incident depression. Future studies are needed to replicate our findings.