Green is Good?


You may have heard that exposure to nature can improve your health*. There are also many trends floating around the Internet that claim to leverage the benefits of nature to improve your physical and mental health. While proponents claim to be driven by evidence, is there really evidence that nature can improve your health? And if so, is it really necessary to reorganise your daily life, drive out to the wilderness, and/or buy expensive accoutrements in order to leverage the benefits?

Popular Claims

Among the most prominent trends is earthing or grounding, a practice popularised by a variety of holistic health devotees, from nature-loving vegans and Ayurvedic enthusiasts to paleo and primal dieters and Silicon valley biohackers. The trend is based on the idea that the earth has a negative charge; but that modern life bombards us with positive charges, creating an imbalance and reducing our ability to combat free radicals. The benefits of grounding touted by advocates are vast, from reducing jetlag to balancing hormones and normalising blood pressure.

A large field under a blue almost cloudless sky

At its most basic, grounding advocates suggest we simply spend more time walking outside on soil and grass in bare feet; but many advocates also promote grounding mats, blankets, shoes, sheets, bags, and a variety of other devices to counteract modern life and provide ready (and overnight!) access to the benefits of the earth through an electrical charge. Most of these sites enthusiastically link to studies, but any effects seen in these small studies are miniscule and potentially the results of design flaws, as described in a recent segment of Skeptics with a K.

Forest bathing is an older cousin of grounding, referring to the Japanese practice of using your senses to soak in the forest atmosphere. Increasingly popular outside of Japan, it has a small number of researchers who suggest it is not only a way to combat the psychological stresses of increasingly urban life but also a way to combat cancer, lower blood pressure, and boost immune function. Although one would think this is a fairly solitary endeavour, as with many holistic practices, its Western reinterpretation includes guided group visits and sometimes even hugging and speaking to trees.People walking along a footpath surrounded by trees

Understanding the connections between exposure to nature and human health

For most people, the idea of sleeping on a specially designed electrical mat and wandering around barefoot in forests are beyond what they are willing to do for health. Access to nature can also be challenging for city dwellers, and in most developed countries, more than 75% of the population lives in urban areas. In the UK that number is over 90%. While cities offer many benefits, urbanisation increases the incidence of a host of health problems and associated socio-economic costs. For these reasons, it’s perhaps more helpful to investigate what we actually know about urban green space and human health, to see if there are measurable benefits.

A tarmac road lined with trees

The evidence

A considerable body of research is developing, suggesting positive impacts of being in, and leaving near, green space. The amount of green space seems more important for perceived health than the amount of urbanisation, although certain groups may benefit more.

The benefits

Exposure to green spaces has been shown to relieve stress and promote relaxation, and has positive impacts on affect and reducing sadness, which improve cardiovascular disease outcomes and all-cause mortality. The effect may be amplified by the fact that people prefer green spaces for physical activity, making exercise and active forms of transport more attractive. Some studies have shown decreases in salivary cortisol and reduced blood pressure, with women potentially more negatively affected by lack of green space. Although some reviews have noted this effect is not consistent across studies.

Increasingly studies are looking at the dose of nature that we actually need to experience these benefits.  Most studies suggest that the required dose is likely relatively small (perhaps only 5-10 minutes on a given day). Benefits are evident whether you are merely looking at nature or exercising in it, although the latter, perhaps understandably, offers benefits more quickly. Lower rates of blood pressure and depression have been documented from just 30 minutes in green space per week. The shape of the dose-response curve is still in question.

A footpath beneath lots of trees with sunlight shining through

Countering harm

It is also worth noting that green space can contribute to reducing air pollution, which is a major contributor to poor human health outcomes. This effect is direct, in that vegetation can reduce greenhouse gas emissions and reduce pollutants such as particulates (PM10), carbon monoxide (CO), ozone (O3), and nitrogen and sulphur oxides (NOx and SOx). Green space makes walking and cycling more attractive. This contributes not only to improving air quality via reduced vehicle use, but the increased physical activity has associated health benefits.

Green space can also reduce the urban heat island (UHI) effect, wherein cities are hotter than surrounding areas because of the prevalence of dark surfaces such as asphalt and concrete. UHI also contributes to poor air and water quality. By lessening this effect, green spaces can improve the urban environment, decrease health impacts of heat and even reduce mortality from heat waves.

Caveats within the literature

There is a lot of academic literature focusing on the connections between human health and urban green space**. This literature is both theoretical and empirical, and methods are a mixed bag. For example:

  • Self-reported data from individuals on perceived improvements in health (usually gathered via questionnaires)
  • Correlations between access to green space and population-level data
  • Direct measurements of key indicators (e.g. blood pressure, heart rate, salivary cortisol) either linked to exposure or accessibility of green space.

What constitutes health varies across studies, with the first two categories often adopting a fairly broad definition that includes physical health as well as mental health (especially anxiety and depression) and broader indicators such as happiness, life satisfaction, and social cohesion.

A body of water with a bridge in the background and trees on either side

As with all social and health research in the “real world”, teasing out causal relationships is difficult. Confounding factors are controlled for, to an extent, but there are so many causal factors that complicate the issue. For example, people prefer to exercise in green space, but green space tends to be more scarce and of lower quality in areas with multiple social, economic, and health deprivations. However increasing green space (and improving its quality, addressing personal safety issues, etc.) can also improve these indicators.

Conclusion

Spending more time in green areas, whether forests urban parks, is likely to offer you some health benefits and encourage you to be more active. The great news is that it needn’t take much of your time, and no special mats, shoes, blankets, or spiritual guides are required. Green spaces also address some of the environmental problems in urban areas, providing benefits for both people and nature.

Dr Sarah Clement standing in front of a wall and smilingDr Sarah Clement

Sarah is a faculty member in the Department of Geography and Planning within the School of Environmental Science at the University of Liverpool. Her research focuses on environmental governance, science-based policy, and nature-based solutions. She is particularly interested in how reforming policy and practice can enable better ecological, socio-economic, and democratic outcomes, particularly during periods of rapid environmental and social change.  Sarah has worked in the field of environmental science and policy for 16 years as an environmental consultant, researcher, and environmental policy advisor in Australia, the UK, and the USA. She is also on the board of the Merseyside Skeptics Society. She spends most of her spare time hiking in nature, travelling, lifting heavy things, adoring her cat, and documenting all of these in pictures. She tweets as @DrSarahClement, and posts said pictures on IG @umsfromumbridge.

 

Footnotes:

* The most widely used definition of ‘health’ is from the World Health Organisation: ‘physical, mental and social well-being, not merely the absence of disease or infirmity’. Operationalising and measuring this concept is a major challenge that leads to the variety of measures discussed here.

** Also called “green infrastructure” and “nature based solutions” in the literature and public policy. To complicate matters, “blue infrastructure” (i.e. water) is often, but not always, embedded in these terms.

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