If this was a medical school lecture, it would start with the name of the subject, in this case “Biophilia” and then look at its Latin roots, something like: Bio- (of life) and -phil (to love). In short, the biophilia hypothesis continues to evolve, as does the term itself given different people attributing a variety of things to the all-encompassing term. Generally, when mentioned with respect to health, it refers to the positive impacts of nature on humans.
There is some controversy in the area surrounding some of the claims of biophilia hypothesis proponents and some of the proposed mechanisms for the effects seen in studies in the realm, but this does not detract from the positive impacts that are seen in the research.
Benefits
Time spent in nature is associated with improved mood and mental health measures in addition to a host of physical health measure improvements. These include; lowered blood pressure, lower measures of stress, improved heart rate variability (for a great substack all about HRV check out Marco’s work), decreased heart rate and some improvements in metabolism (for example improvements in some hormones like adiponectin and reduced blood glucose, though these seem less robust). Additionally, some interesting studies have looked at inpatient hospital setting and found benefits of murals on measures of pain. The collection of these could be explained solely through the effects of stress on the body, that is, lowering stress could improve all of these measures as above, but this is impossible to discern specifically and to be honest is probably immaterial.
Mechanisms
In attempts to better understand the effects, attempts have been made to try and tease out some of the variables. There have been benefits observed through exposure to rooftop gardens for example.
These positive benefits of nature are also present/maintained in part when plants are added to indoor environments. Some of these benefits even seem to be robust enough to be remain present when a view of greenery outside a window is available or even just viewing murals or pictures of nature.
I am not one to blindly buy in to all “traditional” customs being followed because they are tradition. But I do think that there is a lot than can be learned form ancient or older cultures and civilisations. Generally, if something survives an extended period of time, particularly if it isn’t necessarily convenient or efficient, it is worth looking into. For more on this, read about the “Lindy Effect”, though this is neither a direct description of the Lindy Effect nor a perfect example. Which brings us to forest bathing.
Forest Bathing
This originated from Japan and is decades old. It involves people form the city intentionally going out to nature for a ‘bath’. This entails immersing your senses in nature and really slowing down.
There is research showing positive effects on heart rate variability, decreased stress hormones, heart rate and blood pressure as well as improvements in mood from forest bathing. Additionally, there was an increase in NK cell activity (these are important immune cells).
Mechanisms
The exact mechanisms for these benefits are likely multifaceted, but there has been some fascinating research into some of the smells of the forest/trees and volatile organic compounds called “phytoncides”. These are found in many plants, including some you would smell regularly for instance garlic, onions and spices. These phytoncides are used by plants to defend against fungus amongst other things. Like many things in the plant world, what is bad for a fungus, may be slightly stressful to us and thus may help us improve our immune system (a phenomenon known as hormesis).
The research here showed that inhaling the smells of certain plants (specifically hinoki) decreased stress hormones and improved NK cell activity. Similarly, inhalation of compounds from cedar showed positive effects on autonomic function; decreasing heart rate, respiratory rate and blood pressure as well as improving heart rate variability parameters.
Given the low cost and low risk of spending time in nature I would suggest this practice is well worthwhile regardless of perceptions of outcomes or quality of evidence.
Performance
With respect to physical performance, one may ask what impact this has, and reasonably so. I doubt many endurance athletes would say that they prefer indoor or urban environments over nature for their training, but outside of preference, are there any tangible benefits?
Whilst this cannot be answered with significant scientific backing, IF the above indications of the effects of time in nature are indeed the case, it stands to reason these would be robust when considering training likewise.
A reasonable question again is then, don’t we want stress, raised heart rate etc when training?
To which the answer is certainly yes, but as a result of training or perhaps this is best answered in reframing the answer. We want those things but a result of the work we are doing in training (aka training stimulus), not at baseline. So, it seems that training in nature may be beneficial for physical performance, but I will concede this is a bit of a stretch (although again, if anything this costs less and holds almost no risk so it is worth at least experimenting with - for more on decision making lenses check out my article here).
Take Home Messages:
Try get outside for time in nature as often as possible, if you can or it helps, try pair this with other things like exercise/training, socialisation, mediation etc.
Add some greenery in and around your house and workspace or at least have views and/or pictures of it.
REFERENCE LIST
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5. Lee, J., et al. (2011). "Effect of forest bathing on physiological and psychological responses in young Japanese male subjects." Public Health 125(2): 93-100.
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7. Li, Q., et al. (2009). "Effect of phytoncide from trees on human natural killer cell function." Int J Immunopathol Pharmacol 22(4): 951-959.
8. Li, Q., et al. (2007). "Forest bathing enhances human natural killer activity and expression of anti-cancer proteins." Int J Immunopathol Pharmacol 20(2 Suppl 2): 3-8.
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10. Olvera-Alvarez, H. A., et al. (2021). "Associations of Residential Brownness and Greenness with Fasting Glucose in Young Healthy Adults Living in the Desert." Int J Environ Res Public Health 18(2).
11. Pati, D., et al. (2016). "The Impact of Simulated Nature on Patient Outcomes: A Study of Photographic Sky Compositions." HERD 9(2): 36-51.
12. Pearson, M., et al. (2019). "The Physiological Impact of Window Murals on Pediatric Patients." HERD 12(2): 116-129.
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Fantastic article. I've always thought that being in forest may be beneficial because of more oxygen in the air. I'm not sure if that is a hypothesis worth testing, but I feel like I get more of a boost from being in the forest than other areas in nature.