The association between forest cover and depressive symptoms in Pennsylvania adolescents

Abstract

BACKGROUND AND AIM: Exposure to green space, especially dense tree cover, can be beneficial for mental health, but most studies have been conducted with adults. We investigated associations between percent forest cover and depressive symptoms in adolescents in Pennsylvania. METHODS: We assessed depressive symptoms via Public Health Questionnaire-9 scores in 24,985 Geisinger subjects aged 11-18 years (52% females; 93% white; 44% on Medical Assistance) with electronic health records in 2014-16. Percent forest was calculated within a circular residential buffer of radius 463-m (which was converted to a 1250 x 1250 m2 square buffer using “Feature Envelope to Polygon” in ArcGIS)using the most recent release of data (2011) from the U.S. National Land Cover Database with land classes for deciduous, evergreen, and mixed forest and modeled in quartiles. We assessed associations with negative binomial regression models using generalized estimating equations to account for clustering of subjects within communities, adjusted for individual- and community-level covariates. We also used multinomial logistic regression models using generalized estimating equations to evaluate the association between percent forest and clinical depressive score categories of the PHQ-9. RESULTS:The highest quartile percent forest (vs. lowest) was associated with decreased depression symptoms (adjusted exponentiated coefficient = 0.89, 95% confidence interval: 0.83 – 0.96). In categorized models, the highest quartile of percent forest (vs. lowest) was associated with an adjusted odds ratio of 0.80 (95% confidence interval: 0.64, 0.98) for moderately severe to severe depressive symptoms vs. no to minimal depressive symptoms. CONCLUSIONS:Surrounding forest was associated with lower depressive symptoms in a large sample of adolescents. Forest cover could reduce depressive symptoms through promotion of physical activity and reduction of stress. These findings suggest communities should preserve and increase tree cover, a goal that is also consistent with, for example, climate change adaptation for cooling effects and heavy precipitation mitigation. KEYWORDS: mental health outcomes, children's environmental health, health co-benefits