Surrounding residential greenness and mental health: Findings from the French CONSTANCES cohort

This cross-sectional study assessed the association between surrounding greenness and two mental health outcomes according to degree of urbanization in the French CONSTANCES cohort. We included 114,717 participants. Depression in 2018 was evaluated by Center for Epidemiologic Studies Depression Scale (CES-D, from 0 to 60), and psychological distress in 2019 by General Health Questionnaire-12 (GHQ-12, from 0 to 12). Residential surrounding greenness was quantified by the mean of normalized difference vegetation index (NDVI) within 300m circular buffer around residential address. Adjusted negative binomial models were performed to assess the cross-sectional association between a 0.1 increase in NDVI at 300m and each outcome, separately in rural, peri-urban, urban and Paris areas. Stratified analyses by age and sex, and causal mediation models evaluating the role of physical activity were conducted. In 2018, the median age was 48.5, with 54.5 % being women. A 0.1 unit increase of NDVI was associated to lower depressive symptoms in peri-urban areas (incidence rate ratio (IRR) = 0.92; 95 % CI: 0.84–1.00) but higher in Paris (1.21; 1.06–1.38), and no associations were found in urban or rural areas. A 0.1 unit NDVI increase was associated to lower GHQ-12 score in peri-urban (IRR: 0.77; 95 % CI: 0.64–0.93) and urban areas (IRR: 0.79; 95 % CI: 0.65–0.97), with stronger effect size for middle-aged adults in urban areas and men in peri-urban areas. No associations were found in rural or Paris areas. Physical activity showed no mediation role. Surrounding greenness was associated with better mental health in peri-urban and urban but not in rural areas, possibly due to differences in types and uses of greenspaces.