Greenspace, mental health, and psychological well-being: Exploring mechanisms and effect modification

Thesis (Master's)--University of Washington, 2020In an age where humans are spending an unprecedented portion of their time indoors, disconnected from nature and unaware of the ecosystem that surrounds them, research is beginning to unveil the intricate role of nature in human health. Not only does humanity rely on the natural world for food, water, and other ecosystem services, but also for psychological well-being, happiness, and mental health maintenance. Many individuals anecdotally understand that time spent in natural settings can ease negative mental health issues such as stress, anxiety, and depressive symptoms, while encouraging positive psychological states, such as happiness and relaxation. Epidemiologists, ecologists, neuroscientists, and researchers from many other disciplines are digging deeply into these ideas, transforming anecdotes into scientific research, and uncovering the mechanisms underlying the connection between mental health and natural environments. They are also exploring whether and to what extent existing trends between greenspace exposure and benefits to mental health may differ among different populations and individuals. To build upon this body of work and help fill critical research gaps, I conducted two research projects– an environmental epidemiological analysis of data from a large-scale health cohort and a narrative literature review on the Japanese health practice of forest-bathing. The first project utilized data from the Multi-Ethnic Study of Atherosclerosis (MESA), an epidemiologic cohort study with 6,814 participants from six sites across the US. In this analysis, I tested for association between residential proximity to greenspace, measured by the normalized difference vegetation index (NDVI), and scores from the Center for Epidemiologic Studies (CES) Depression Scale, a measure of depressive symptoms. To determine the role of individual-level characteristics in modifying this relationship, I assessed the degree to which chronic burden, a proxy for chronic stress, modified the effects of greenspace on depressive symptoms. This allowed me to determine if highly burdened individuals have pronounced mental health benefits associated with exposure to greenspace. The second project was a narrative literature review on the mental health and psychological well-being benefits of forest exposure. This review builds upon the forest-bathing literature by exploring potential biological and psychological mechanisms underlying the association between forest terpene exposure and benefits to human health. Together, these two projects contribute to the growing body of nature and health literature by diving deeper into mechanistic pathways and by determining the role of individual-level characteristics in the effect of nature on mental health and well-being