Outdoor blue spaces, human health and well-being: A systematic review of quantitative studies

Background: A growing number of quantitative studies have investigated the potential benefits of outdoor blue spaces (lakes, rivers, sea, etc) and human health, but there is not yet a systematic review synthesizing this evidence. Objectives: To systematically review the current quantitative evidence on human health and well-being benefits of outdoor blue spaces. Methods: Following PRISMA guidelines for reporting systematic reviews and meta-analysis, observational and experimental quantitative studies focusing on both residential and non-residential outdoor blue space exposure were searched using specific keywords. Results: In total 35 studies were included in the current systematic review, most of them being classified as of "good quality" (N = 22). The balance of evidence suggested a positive association between greater exposure to outdoor blue spaces and both benefits to mental health and well-being (N = 12 studies) and levels of physical activity (N = 13 studies). The evidence of an association between outdoor blue space exposure and general health (N = 6 studies), obesity (N = 8 studies) and cardiovascular (N = 4 studies) and related outcomes was less consistent. Conclusions: Although encouraging, there remains relatively few studies and a large degree of heterogeneity in terms of study design, exposure metrics and outcome measures, making synthesis difficult. Further research is needed using longitudinal research and natural experiments, preferably across a broader range of countries, to better understand the causal associations between blue spaces, health and wellbeing.