Nature, biodiversity and human health: how strong is the evidence?

In recent years there has been a growing recognition of the vital links between the natural environment and human health and wellbeing – one of the BES’s policy priorities. The UK Government’s Natural Environment White Paper explicitly acknowledges that “human wellbeing is intimately connected with our natural environment”, whilst the RSPB and The Wildlife Trusts are leading calls for a “Nature and Wellbeing Act”, based on the view that there is “considerable evidence to show that contact with nature can help to prevent and reverse poor health and wellbeing”. This link is also finding greater resonance with public health professionals, as demonstrated by the Faculty of Public Health’s call to make better use of our “natural health service”.

New study assesses the state of our knowledge

But how well do we really understand the connections between nature and human health and wellbeing? How strong is the evidence on which we can base policy decisions in this emerging area? A new study by Paul Sandifer, Ariana Sutton-Grier and Bethney Ward, published in the journal Ecosystem Services, has attempted to assess the state of knowledge on the relationship between nature and biodiversity, and human health and wellbeing: what they term the “ultimate” ecosystem service. The paper is based on a literature review across disciplines including ecology, public health, biomedical sciences, urban planning and psychology.

In some cases, the evidence is reasonably strong. The authors find that there is a large and growing body of research suggesting that human exposure to nature – understood in a broad sense as the “physical and biological world not manufactured or developed by people”, has a number of positive effects on health and wellbeing. This research is largely based on comparative studies contrasting health outcomes in urban spaces with those in “green” or natural settings, and suggests that there are a number of both mental and physical health benefits of contact with nature, including positive effects on mood, healing, heart rate, blood pressure, stress and concentration. However, the authors caution that many studies lack rigour, for instance in terms of adequate controls, sample size or duration, and on the whole remain correlative, rather than offering causal explanations.

While the link between contact with nature and human health is relatively clear, does the quality of the natural environment in question matter? Does a species-poor city park deliver the same benefits as a highly biodiverse ancient woodland? The review finds that the evidence for a direct relationship between biodiversity and health outcomes is currently limited, but with some intriguing emerging findings. A few studies have suggested that exposure to diverse natural habitats and many different species has an impact on health outcomes: for example research by Fuller et al across urban green spaces in Sheffield found that increased species diversity, or perceived diversity, had a positive impact on health and wellbeing outcomes. And while there is mixed evidence for the role that increased biodiversity has on mitigating the emergence and transmission to humans of infectious diseases, it has been convincingly demonstrated that human exposure to diverse natural habitats – and thus microbial diversity – is critical for the development of immune response to allergens.

Future research directions and policy implications

While the evidence base is growing, there are a multitude of questions about the relationship between nature and human-health that remain unanswered, and Sandifer et al offer a number of recommendations for further interdisciplinary research priorities. We currently have numerous case studies illustrating the impact of nature, and in some cases biodiversity, on human health and wellbeing, but little understanding of the mechanisms that explain how and why these effects occur. Similarly, systematic, large-cohort studies using health data are required to tease out the long-term, population level effects of contact with the natural environment on health, using appropriately designed metrics for both biodiversity and health and wellbeing.

As our understanding of the links between nature, biodiversity, and human health and wellbeing grows, several policy implications emerge. For public health, there is the possibility of making greater use of nature as a tool for delivering health outcomes. For conservation, the importance of green spaces and biodiversity for health and wellbeing offer a persuasive argument for protecting ecosystems. These opportunities are particularly pronounced in urban areas where access to nature is often constrained – a point underlined in the recently launched final report of England’s Natural Capital Committee, which highlights enhancing urban green spaces as a natural capital investment priority that could deliver savings of over £2 billion a year in averted health costs. Sandifer et al go further, suggesting that we require a wholesale re-envisioning of urban and spatial planning tgat “places human health and wellbeing at the centre, facilitates human interaction with nature (…) to the fullest extent possible, and ensures people are surrounded by and have access to biologically diverse natural habitats”.

Such a reorientation of the planning system is a highly ambitious goal. But as the relationship between nature and human health becomes clearer, it is certain that ecological knowledge and solutions will have an increasingly important role to play in informing policies that deliver for both people and the environment.