Urban residential tree canopy and perceived stress among pregnant women

Objective: To examine the association of urban residential tree canopy cover with perceived stress in a cohort of pregnant women in Philadelphia, PA, and explore whether this association differed among participants with a history of anxiety and depression. Study design: We performed a secondary analysis of 1294 participants of the Motherhood & Microbiome (M&M) pregnancy cohort who lived in Philadelphia, with first visit perceived stress (Cohen's Perceived Stress Scale, PSS14), and key covariate data. Tree canopy cover was calculated as percent cover within 100 and 500 m radii buffers around participants' homes. We performed multilevel mixed effects linear regression models, with perceived stress as the dependent variable. The main independent variable was tree canopy coverage. Individual level covariates included season of last menstrual period, history of depression or anxiety, race/ethnicity, insurance, parity, and age. Census tract neighborhood deprivation index was used to account for area-level socioeconomic confounding variables. We also examined whether a history of anxiety or depression, modified the association between tree canopy coverage and perceived stress. Results: Most participants were non-Hispanic Black (70.6%, n = 913), on Medicaid or uninsured (60.4%, n = 781), and 15.8% (n = 204) of participants had a prior history of depression or anxiety. We did not detect associations between tree canopy coverage and perceived stress overall. However, we detected effect modification; among participants with a history of depression or anxiety, each standard deviation increase in tree canopy cover was associated with lower PSS-14 in 100 m buffers (beta-1.0, 95% CI-1.8,-0.2), but not among participants with no histories of depression or anxiety (beta 0.2, 95% CI-0.3, 0.7) (interaction P = 0.007). Results were similar in directionality but not statistically significant within 500 m buffers. Conclusion: Residential tree canopy coverage was associated with reduced perceived stress among urban-dwelling pregnant women with history of anxiety or depression. Future studies of the effects of greenness and other stress reducing efforts should consider underlying mental health conditions as effect modifiers.