Health Benefits from Nature Experiences Depend on Dose
Nature within cities will have a central role in helping address key global public health challenges associated with urbanization. However, there is almost no guidance on how much or how frequently people need to engage with nature, and what types or characteristics of nature need to be incorporated in cities for the best health outcomes. Here we use a nature dose framework to examine the associations between the duration, frequency and intensity of exposure to nature and health in an urban population. We show that people who made long visits to green spaces had lower rates of depression and high blood pressure, and those who visited more frequently had greater social cohesion. Higher levels of physical activity were linked to both duration and frequency of green space visits. A dose-response analysis for depression and high blood pressure suggest that visits to outdoor green spaces of 30 minutes or more during the course of a week could reduce the population prevalence of these illnesses by up to 7% and 9% respectively. Given that the societal costs of depression alone in Australia are estimated at AUD$12.6 billion per annum, savings to public health budgets across all health outcomes could be immense.
Urbanization is emerging as one of the most important global health issues of the 21st century 1, 2, with cities becoming epicenters for chronic, non-communicable physical and mental health conditions 3, 4. There is growing recognition of the crucial role of urban green spaces in addressing this public health challenge 5, 6, with over 40 years of research showing that experiences of nature are linked to a remarkable breadth of positive health outcomes. This includes improved physical health (e.g. reduced blood pressure 7 and allergies 8, lower mortality from cardiovascular disease 9, improved self-perceived general health 10, 11), improved mental wellbeing (e.g. reduced stress 12 and improved restoration 13, 14), greater social wellbeing 15, and promotion of positive health behaviors (e.g. physical activity 16, 17). Consequently, cities across the world are investing in the provision, management and enhancement of public green spaces, with the 100 largest cities in the US alone spending over US$6 billion in 201518. Advice about how to achieve health outcomes from green spaces currently remains very general 19, 20. Evidence on how frequent or how long nature experiences need to be, or what types of nature are needed, is vital to ensure that investment in green space provision can cost-effectively help to meet the public health challenges of urbanization 21, 22, 23.
Here, for the first time we use the nature-dose framework posed by Shanahan et al.21 to quantify the link between health outcomes and experiences of nature, as measured by intensity (i.e. the quality or quantity of nature itself), and the frequency and duration of a city resident’s experiences. We focus on examples of health issues across four domains for which there is some prior evidence that nature exposure can provide benefits. These health issues are also particularly relevant for cities, and include mental health (the prevalence of depression), physical health (high blood pressure), social wellbeing (social cohesion), and a positive health behaviour (physical activity). These health outcomes could be tied to experiences of nature through a range of mechanistic pathways (some of which are outlined in Fig. 1)22. For example, a higher level of vegetation within a landscape (a measure of nature intensity) may be linked to enhanced physical, mental and social wellbeing through providing a visually complex environment that can lead to reduction in stress24, reduction of mental fatigue 25, or by adding to the look and feel of a place and so providing a pleasant location for social or physical activities 22 (Fig. 1). Similarly, variation in duration and frequency of nature exposure could also influence the long-term health outcomes people experience, with even short-duration exposure to natural environments shown to deliver an immediate reduction in blood pressure 7 and greater feelings of restoration 26. Yet despite this, whether and how the intensity, frequency or duration of nature exposure leads to long-term and lasting effects on health remains unexplored.
Figure 1: Hypothesized pathways to the mental, physical, social and behavioral health outcomes from experiences of nature explored in this study, based on the framework outlined by Shanahan et al.22.
Unpacking the relationship between health outcomes and the three components of nature dose also allows for the exploration of dose-response relationships, including whether there is a minimum dose where some effect of natire on health might be seen21,27. Here we therefore use dose-response modelling to determine how rates of high blood pressure and depression vary in response to nature experiences, including whether the outcomes plateau or continue to improve21. We examine the scale of the population health benefits that could arise if these nature dose recommendations are met, and the impact of this on the public health purse.
How to cite this article: Shanahan, D. F. et al. Health Benefits from Nature Experiences Depend on Dose. Sci. Rep. 6, 28551; doi: 10.1038/srep28551 (2016).