Comparison of indoor versus outdoor mindfulness interventions for veterans: A pilot randomized controlled trial

Veterans' reluctance to engage in mental health treatment coupled with high attrition in such treatment should motivate practitioners and researchers to create innovative ways to treat veterans. Nature-based interventions show promise as a means for addressing veterans' mental health needs. The present study aimed to test the feasibility and acceptability of a manualized nature-based mindfulness intervention for veterans with mental illness. The authors hypothesized that veterans participating in the outdoor, nature-based intervention would report greater reductions in posttraumatic stress disorder symptoms and psychological distress compared to those participating in an indoor mindfulness intervention. Recruited from a Veterans Affairs health care center, 41 veterans with diagnosed mental illness were randomized to either a six-session outdoor group mindfulness intervention or a comparable six-session group mindfulness intervention delivered indoors at the Veterans Affairs. A t test and chi-square tests were used to examine treatment session attendance and treatment completer status. An intent-to-treat framework was used to assess between-group differences by fitting separate generalized linear mixed models with robust estimation for the outcomes of posttraumatic stress disorder symptoms, psychological distress, sense of restoration, and nature connectedness. Results showed that, while the average number of training sessions attended did not statistically differ by group, the number of treatment completers did; there were more treatment completers in the outdoor group. Additionally, linear mixed modeling with robust estimation revealed a significant Condition × Time interaction for posttraumatic stress disorder symptoms. The findings of this research demonstrate that nature-based interventions show promise as an approach to treating veteran mental illness while combating mental health care stigma and increasing treatment completion rates. (PsycInfo Database Record (c) 2026 APA, all rights reserved).