Exposure to green, blue, and biodiverse spaces and their associations with loneliness in urban adults: Findings from the EPIPorto cohort.

Emerging evidence suggests green space may reduce loneliness, while the role of blue space and biodiversity remains under-researched. This study examines associations between exposure to green, blue, and biodiverse spaces and loneliness in adults in Porto, Portugal and explores potential effect modifiers. Loneliness was assessed in 2022 in 657 EPIPorto cohort participants using the UCLA Loneliness Scale (>32 indicating 'high loneliness'). Vegetation and surface water were measured using Normalized Difference Vegetation Index (NDVI) and Modified Normalized Difference Water Index (MNDWI) within 100m, 300m, and 500m pedestrian buffers. Biodiversity was assessed using a species richness index. Cross-sectional associations between these variables and loneliness were estimated with linear regression (robust standard errors) and logistic regression. Additional models considered long-term trends of NDVI and MNDWI since baseline (1999). Effect modification of sex, marital status, cohabitation and age was assessed through multiplicative interactions. Models were adjusted for confounders, including markers of socioeconomic status. Cross-sectionally, greater amounts of vegetation within 100m [β per one-unit increase = -1.555, 95 %CI (-3.090; -0.007)] and higher species richness within 300m and 500m [-0.514 (-1.027; -0.001) and -0.581 (-1.132; -0.031)] were associated with lower levels of loneliness, while blue space presence showed non-significant associations. Concerning long-term trends, the results lacked significance. Non-significant results were found for loneliness as a binary outcome and no effect modification was confirmed. This study suggests that near home greenness and biodiversity may reduce levels of loneliness, while the association with blue spaces is inconsistent. This highlights the potential of urban greening and biodiversity to help mitigate loneliness.