Depression risk among college student witnesses to on-campus potentially traumatic events: the roles of bystanding, upstanding, and prosocial campus climate.

Witnessing traumatic events is a community-level exposure linked to poor mental health. Among college students, witnessing events such as assault on campus is common yet understudied as a public health concern. This study examines how witnessing potentially traumatic events (PTEs) and students' behavioral responses-bystanding (not intervening) and upstanding (intervening)-relate to depression risk, and whether prosocial campus climate mitigates this risk. Data were drawn from the 2022-2023 cohort of the Healthy Minds Study, a national sample of U.S. college students (N = 66,474; Mage=21.14 years). Measures included past-year witnessing of on-campus PTEs, past-year bystanding and upstanding, prosocial campus climate, and depression symptoms (PHQ-9), which were dichotomized into elevated risk for at least moderate major depressive disorder (PHQ-9 ≥ 10) versus no elevated risk. Logistic regressions estimated associations among witnessing, behavioral responses, prosocial climate, and depression risk. Nearly 25% of students witnessed one or more past-year on-campus PTEs. Each additional witnessed event was associated with 13% increased odds of elevated depression risk. Bystanding was not significantly associated with depression risk, while each upstanding behavior was linked to 8% increased odds. Each one-point increase in perceived prosocial campus climate was linked to 25% decreased odds of elevated depression risk, regardless of past-year upstanding. Findings highlight the complex mental health correlates of witnessing and responding to campus-level trauma. Prosocial campus climate appears protective at the community level, underscoring the value of community-based strategies to support student mental health in the context of shared traumatic exposures.