Background:
Evidence is growing that contact with the natural environment in green and blue spaces has a beneficial impact on population physical and mental health and wellbeing. There are now many public health and local initiatives to promote physical activity, not only in the gym, but also in outdoor spaces such as green parks (e.g. countryside; forests; town and city parks) and blue spaces (rivers; lakes and the sea). Over 50% of the population of the UK live within an hour of a National Park however, there is little economic evidence available on population health benefits and value of accessing green and blue outdoor spaces. The aim of this study is to investigate the economic evidence associated with the health benefits of using green and blue spaces.

Methods:
A systematic literature search in line with PRISMA guidelines is being conducted. Peer-reviewed articles are sought using health economic databases, scrutiny of reference lists, experts and grey literature to answer the following research questions: Firstly, what evidence is there of the cost-effectiveness of nature based health interventions and the greening of healthcare? And secondly, are there any standard tools for economic evaluation?

Results:
All relevant papers meeting the initial inclusion criteria are being critically appraised for methodological quality using a Critical Appraisal Skills Programme (CASP) checklist. The review questions will be addressed and a narrative summary of results for costs associated with valuing nature in terms of using green and blue spaces for health benefits will be produced. If homogenous studies are found, meta-analyses will also be conducted.

Conclusions:
Standard tools for evaluating the economic evidence relating to green and blue spaces and health benefits will be described in economic evidence tables (cost-effectiveness, cost utility, cost-benefit analyses, return on investment and social return on investment). A new economic-evidence tool will be created if none already exist.