Comparing visual-exposure and spatial proximity/coverage metrics of urban blue space in relation to depression-related outcomes: a systematic review and meta-analysis.

Background: Urban blue spaces are increasingly examined in relation to mental health, but findings remain difficult to interpret because visual-exposure metrics and spatial proximity/coverage metrics may capture different exposure dimensions. This systematic review and meta-analysis synthesized observational evidence on urban blue-space exposure and depression-related outcomes in adults and compared these two metric categories. Methods: Following PRISMA 2020, six English and Chinese databases were searched for observational studies published from January 1, 2000, to March 31, 2026. Eligible studies included adults aged 18 years or older and reported depression-related outcomes. Continuous outcomes were synthesized as standardized mean differences using random-effects meta-analysis, and certainty of evidence was assessed using GRADE. Results: Eight observational studies involving 35,797 adults were included; six studies involving 20,383 participants contributed to the continuous-outcome meta-analysis, whereas two binary-outcome studies were summarized narratively because of differences in outcome ascertainment and exposure modeling. Greater blue-space exposure showed a very small inverse association with depression-related outcomes (SMD = -0.04, 95% CI: -0.06 to -0.02; I Conclusions: Current observational evidence suggests a trivial inverse association between urban blue-space exposure and depression-related outcomes in adults. Differences between visual-exposure and spatial proximity/coverage metrics should be interpreted descriptively because subgroup differences were not statistically significant and certainty of evidence was very low. These findings may help refine exposure classification but do not support causal or planning-level conclusions.