Exposure to surrounding greenness and well-being in Portugal, a cross sectional study

BACKGROUND: Positive mental health effects of nature have been studied before with relevant associations between the two easily found in literature. However, there is still a lack of population based studies that focus on the effect that the amount of surrounding greenness might have on well-being. OBJECTIVES: This study aims to evaluate the effects of exposure to surrounding greenness in the residential area with well-being based on the Mental Health Inventory 5-items (MHI-5) score from 0-100 (less to more well-being). METHODS: We used data from participants of the 2015 National Health Examination Survey (INSEF) which uses complex sampling methods to represent the Portuguese population and includes 4911 participants. Data regarding socioeconomic status, urbanization level, education, sex, age, postal code and well-being score was extracted. We then calculated the average surrounding greenness using the Normalized Difference Vegetation Index (NDVI) in a 300m and 1km buffer around each participant's residency and divided it by tertiles (from less green to most green). Log linear regression models controlling for confounder effects were applied. RESULTS: For the 300m buffer living in the 2nd tertile of greeness compared to the 1st tercile decreased the average well-being score by around 4% (ExpB=0.969, 95% p < 0.05). Living in the 3rd tercile (most green) had less to almost no effect (ExpB=0.989, 95% p < 0.05). Sensitivity analysis in a 1km buffer and the stratified analysis for sex and urbanization, also show a 4% decrease in well-being in the 2nd tertile and little to no effect in the 3rd. DISCUSSION: This study has found an association that is contrary to most literature on this subject, the study design might be subject to selection biases and misclassification of exposure. Further analysis should be done with relation to qualitative aspects of green space, accessibility to green areas and the roles of social cohesion and physical activity. KEY MESSAGES: • Population based study done in Portugal regarding the association between well-being and surrounding greenness. • Findings point to a negative association between increased surrounding greeness and well-being.