Effects of Home Neighborhood Tree Canopy Coverage on Mental Health Outcomes: A Traumatic Brain Injury Model Systems Investigation

Objective: Explore the relationship between tree canopy coverage (TCC) in one's home neighborhood and mental health outcomes, and how these relationships differ by home neighborhood factors, among persons with traumatic brain injury (TBI) in the United States. Setting: Community. Participants: Enrolled in the TBI Model Systems National Database with completed follow-up interview after January 1, 2017. Design: Secondary analysis of cross-sectional data. Main Measures: Neighborhood (census tract) Percent TCC, depressive (Patient Health Questionnaire-9) and anxiety (General Anxiety Disorder-7) symptoms (scores ≥10 on each measure), personal/demographic (age, sex, education, homebound status), and neighborhood factors (type, socioeconomic disadvantage). Results: Separate negative binomial regression models were constructed for the 2 mental health outcomes (depression and anxiety symptoms). Covariates in final models were age, sex, neighborhood type, Functional Independence Measure (FIM) total (concurrent), driving status, homebound status, and neighborhood-level socioeconomic disadvantage. The interaction between Percent TCC and neighborhood type (but not homebound status) was significant for depression and anxiety symptoms. The nature of the significant interaction was such that, for both mental health outcomes, those living in rural neighborhoods with higher Percent TCC were more likely to have moderate to severe mental health symptoms. However, this effect was attenuated after adding neighborhood level socioeconomic disadvantage, suggesting that part of the effect may be due to socioeconomic characteristics of rural versus other neighborhoods. Conclusions: After adjusting for SDoH, the direct effect of TCC on mental health after TBI was small and opposite the direction hypothesized (higher TCC associated with poorer mental health), particularly for those living in rural neighborhoods potentially more likely to experience socioeconomic disadvantage. Our findings highlight the importance of evaluating interactions between different aspects of the social (eg, SDoH), natural (eg, greenspace), and built (eg, neighborhood type) environment to provide a comprehensive understanding of factors affecting health after TBI.