Introduction

Have you noticed how Japanese books are crushing it on the bestsellers list recently? I have cleaned out my sock drawer having read ‘The Life-Changing Magic of Tidying’. I tried to be all ‘Ikigai’ by using the Japanese secret to a long and happy life. I even had a short (unsuccessful) dalliance with ‘Kakebo’ or the art of Japanese domestic accounting.

Just this week, I have just finished reading ‘Shinrin-yoku – The Art and Science of Forest Bathing. How Trees Can Help You Find Health and Happiness’ which was written by Dr Qing Li from Nippon Medical School, Japan. Forest bathing (now upgraded to forest medicine in Japan) is just one of the many techniques used in ecotherapy, green therapy or nature assisted therapy.

Ecotherapy is promoted as a way to help us reduce BP, manage stress, increase energy, boost immunity, loose weight, lower blood sugar levels and reduce cardiovascular disease risk. Sounds great, but does ecotherapy actually do any of the above?

Dr Li is clearly passionate about forest medicine and reminds us that both Buddha and Newton had their major ‘a-ha’ moments sitting under trees. He believes that this was no coincidence. He tells us that we all intuitively know that being out in nature feels great.

This intuitive knowing is called ‘yūgen’ in Japanese. However Dr Li reminds us that he is a scientist and not a poet and that we need more than just ‘yūgen’. We need science. Very #healthybutsmart, Dr Li.

In his book, Dr Li presents the results of some of his studies. As the book is written for a general population (and not the #healthybutsmart crew), he does not share any nitty-gritty details (aka statistics). In this article we go behind the scenes of the ecotherapy to see for ourselves what the science shows.

What Is Ecotherapy?

Ecotherapy refers to connecting with nature in order to improve our health and wellbeing. Numerous theories have been suggested to explain a possible link between ecotherapy and wellbeing.

One theory for ecotherapy is a principle known as biophilia (1). Biophilia was popularised by an American biologist, E O Wilson, in 1984. According to this theory, humans are genetically hardwired to love nature. We love nature because we love things that give us a survival advantage. (I hate to argue, but if this is the case, why do my kids love candy and hate broccoli?)

Another theory relates to the fact that we have an internal body clock known as the circadian rhythm. Our circadian rhythm is influenced by nature. Maybe being in nature helps re-set our circadian rhythm and improves our health?

The next theory suggests that it is all about phytoncides. Phytoncides are aromatic terpenes that are released from trees as part of their natural defence mechanism. Phytoncides released from trees include limonene, pinene and camphene. Think of that unmistakeable smell of a pine forest. It has been suggested that these aromatic compounds act like a form of aromatherapy and help relax the mind and body.

Yet another theory relates to the hygiene hypothesis. This hypothesis suggests that inadequate exposure to pathogens (such as those found by being out and about in nature) at a young age can increase the risk of immune mediated diseases at a later stage in life.

Finally, we have the paleo-deficit disorder theory. According to this theory, our evolutionary development as humans has failed to keep up with our industrial development. We are still hard wired to be caveman and as cavemen, we long for nature.

Ecotherapy covers a wide range of nature based therapies that include:

  • Forest Bathing or Forest Medicine
  • Barefoot Walking
  • Outdoors yoga
  • Outdoors meditation
  • Horticultural therapy
  • Wilderness therapy
  • Gardening
  • Flower therapy

Is There Any Research?

Yes, but it is difficult to determine how much research there is exactly. Many publications on this topic are published in non-traditional or niche journals which may or not be indexed. There are very few publications for the search term ‘ecotherapy’. Expanding this to nature assisted therapy gives us almost 2000 publications and 80 clinical trials.  Drilling down deeper to forest bathing (as an example) gives us 85 publications and 6 clinical trials.

However, not all research is created equally as we know. A 2016 systematic review to see if taking part in activities that enhance the natural environment (such as maintaining paths to access the countryside) can improve people’s physical and mental health initially identified 21,420 records but exclude all but 19 of these as being of poor-quality or irrelevant (2).

Is there Soil That Acts As An Antidepressant?

 There are two main angles to consider for this topic and the potential role for soil in health in general.

Firstly, as mentioned above there is the hygiene hypotheses. This basically says that rates of certain diseases like asthma and multiple sclerosis are higher in people who grow up in sterile environments.

It is claimed that exposure to pathogens (including soil pathogens) can help develop a healthy immune system. Additionally exposure to soil and particularly worms are speculated to divert the immune system and reduce the risks of immune based diseases.

Secondly, there is great interest in a particular bacteria called Mycobacteria vaccae. This bug is present in the soil and is believed to have the potential to lift our mood.

American based researchers examined the potential influence of bacteria such as Mycobacterium vaccae on the gut-brain-microbiota axis. Mice fed live M. vaccae prior to and during a maze learning task demonstrated a reduction in anxiety-related behaviors and maze completion time, when tested at three maze difficulty levels over 12 trials for four weeks (3).

A study just published this year showed that mice who were vaccinated with Mycobacterium vaccae prior to a forced swim showed activation of  subsets of serotonergic neurons in the brain which was associated with antidepressant-like behavioral responses (4).

Bottom Line

All very interesting but there is really nothing really substantial to link soil to health at this stage.

Do “Negative Ions” Affect Your Health?

Negatively charged ions are generated by moving air and water eg: storms, showers, waterfalls.

Negative ions are believed to offer health benefits and have been called ‘air vitamins’. I have come across articles on negatively charged ions in a number of magazines and often wondered about the validity of the claims. Is a shower better than a bath? It turns out that there are handful of studies to guide us here.

 A study of 73 women with seasonal affective disorder compared using a placebo, red light, high or low density ions for 12 consecutive days (5). They found that bright light was significantly more effective than the other three interventions at lifting the mood of these women. High density ion therapy was non-statistically more significant than placebo in the study.

Wesleyan University researchers studied 32 adults with major depression and randomized them to bright light, high density negative ions or low density negative ions (6). These interventions were used for one hour per day over 5 weeks. In this study high flow negative ions was defined as 4.5 x10(14 )ions/second) while low flow rate was 1.7×10(11) ions/second. The remission rates were 50% for bright light, 50% for high density ions and 0% for low density ions.

One of the lead researchers in this field is best selling author, Michael Terman. One of his most influential studies involved enrolling 99 adults with depression and dividing them into groups: dawn simulation, light therapy, high flow negative ions or low flow negative ions (7). Similar definitions for high versus low density ions were used in this study.

Statistically significant improvements in an administered depression rating score were noted with dawn simulation, light therapy and high density ions.

Bottom Line

Very preliminary data in small studies suggest (but do not prove) some possible health benefit for high flow negaitve ions but no benefit for low flow negative ions.

Is Playing Outdoors Helpful For Children With ADHD?

I am going to say a big yes here. Researchers from Oregon have just published a ‘draw and tell’ study with 20 children with ADHD (11). These children were asked to draw things that made them feel good.

Most children (90%) described engaging in some form of activity, often outdoors, and with others. Nature featured directly and indirectly in 85% of the feedback from the children. Children shared that doing things, outdoors, with others, made their life “really good”.

Bottom Line

If being outdoors makes children with. ADHD feel ‘really good’ that is enough for me to give this the green light.

Are There Health Benefits To Exercising Outside rather than Inside?

The hypothesis that there are added beneficial effects to be gained from performing physical activity outdoors in natural environments is very appealing and has generated considerable interest (unless you own a gym that it is). My personal bias is that I would think that this is true from my own experience.

A systematic review compared the effects on mental and physical wellbeing, health related quality of life and long-term adherence to physical activity, of participation in physical activity in natural environments compared with physical activity indoors (11).

They included eleven trials (833 adults).  Exercising in natural environments was associated with greater feelings of revitalization,  positive engagement, decreases in tension, confusion, anger, and depression, and increased energy. Participants reported greater enjoyment and satisfaction with outdoor activity and declared a greater intent to repeat the activity at a later date.

None of the identified studies measured the effects of physical activity on physical wellbeing or the effect of natural environments on exercise adherence. The one blooper with this was calmness which oddly enough may be decreased following outdoor exercise?

Bottom Line

Outdoor exercise seems to offer range of  benefits over outdoor exercise with the exception of calmness.

Does Walking in a Park Reduce Stress?

There is some overlap between this section and the section above but here we are focusing specifically on stress or the physiological stress response.

Norwegian investigators enrolled 14 office based workers in a study comparing exercise-based intervention in the workplace, either outdoors in a green/nature area or in an indoor exercise-setting (12)

The intervention consisted of an information meeting and two exercise sessions, each including biking and a circuit-strength sequence using elastic rubber bands.The group that exercised outdoors were found to have statistically higher environmental potential for restoration, positive effects on mood and improved cortisol levels (p < 0.001).

A study published by our very own Dr Qin Liu in 2016 showed that a short leisurely walk in the forest offered health benefits (13). In this study, 19 men (aged 40-69) were recruited from newspaper ads in Japan.

Entry criteria into the study included having hypertension and not being on anti-hypertensive medications. The study participants participated in two walks over 2.6 km each over 80 minutes. The first walk was in a non-tree lined urban setting followed one week later by a forest walk. The study found significant decreases in anxiety, depression, fatigue, anger and confusion.

They also found significant decreases in urinary dopamine and non statistically significant deceases in urinary adrenaline.

There was no significant difference between the groups in BP (mathematically speaking). However the authors expected an increase in BP in the forest as the temperature in the forest was lower than that in the city and low temperatures are usually associated with incerases in BP. This lead them to conclude that forest walks do have a beneficial effect on BP.

Finally, a 2018 study from researchers in Philadelphia reviewed all available data on stress responses to deliberate exposure to outdoor environments in a paper  entitled ‘Does spending time outdoors reduce stress? A review of real-time stress response to outdoor environments.’ They included nature viewing, outdoor walks, outdoor exercise and gardening in the review paper. (14).

They overall conclusion was that heart rate, blood pressure, and self-report measures provide evidence that spending time in outdoor environments, particularly those with green space, may reduce the experience of stress, and ultimately improve health.

Bottom Line

Available data shows a link between being outdoors and reduced stress. However, this does not necessarily mean that ‘being outdoors’ itself has a direct anti-stress effect. As an example, perhaps being outdoors means that we are not working indoors on our computers and that it is the absence of being indoors that gives us health benefits?

Does Being Outside More Improve Your Eyesight?

There are a number of publications on the subject. The most useful and up to date paper is a review paper published just last year (8). Chinese investigators identified 51 articles with relevant data. On closer examination of the 51 articles, 25 were included in the meta-analysis (23 of the 25 articles involved children).

They used a bewildering array of sophisticated statical analysis including a Mantel-Haenszel random-effects model. I was pretty myopic myself by the time I finished slogging through the statistics. Overall, the study found that increased time outdoors is effective in preventing the onset of myopia as well as in slowing the myopic shift in refractive error. Paradoxically, outdoor time was not effective in slowing progression in eyes that were already myopic.

Please forgive the terrible pun, but I took a closer look at the data to understand this better.

A study of 946 individuals in a 20 year Australian cohort found that myopic participants had significantly lower vitamin D levels compared to study participants with normal vitamin D levels (9). While this is not direct evidence that being outdoors can help eyesight, it certainly adds plausabilty to the theory. Vitamin D is known as the sunshine vitamin and it is certainly possible that vitiamin D is a surrogate marker for being outdoors in this study.

That was my theory when I first read this study but it turns out I was wrong. Well, half wrong anyway. A longitudinal study in almost 4000 children found that total vitamin D and vitamin D3 were biomarkers for time spent outdoors, however there was no evidence they were independently associated with  myopia (9).

Bottom Line

There is evidence that being outdoors can improve eyesight, thought it is unclear as to how exactly this might happen.

The Vitamin D Factor?

Vitamin D is known as the sunshine factor. Sunlight converts 7-dehydrocholesterol to cholecalciferol or vitamin D3  and boosts our vitamin D stores (15).

Vitamin D is known to offer important health benefits. Probably the best known health benefits of vitamin D relate to bone health but there a number of others(16). A 2016 Cochrane review found that vitamin D can reduce steroid use and ER visits related to asthma (17).

The value of sun therapy (or heliotherapy) goes beyond just vitamin D production . UVA radiation releases nitric oxide which also lowers blood pressure. During active exposure to UVA, diastolic blood pressure in one study fell by roughly 5 mmHg and remained lower for 30 minutes after exposure (18).

Sun exposure carries risks too and care has to be taken to minimise the risks of skin damage or skin cancer with excessive sun exposure (14).

Bottom Line

Sunlight has beneficial effects on health including (but not limited to) boosting vitamin D levels which in turn has known health benefits. This has to be balanced against the risks of excessive sun exposure and particularly skin cancers.

Is Ecotherapy Safe?

There are no helpful studies looking at the safety of ecotherapy. Are there risks to being outdoors?

Sure, but common sense can prevail and protect us. Think back to the skills you learned as a scout or girl-guide.

Just because we decide to become eco-warriors in our lunch break does not mean we can leave all common-sense behind. As mentioned above, excess sun exposure can be harmful.

Some outdoor environments carry the risk of insect bites which can transmit disease eg ticks and mosquitoes.

Foraging for food is definitely not an amateur sport. It can be difficult to differentiate between edible and toxic mushrooms.It is important to have a health check before deciding to head off into the wilderness and of course, it is essential to bring your own regular or rescue medications with you. A bird-watching or forest bathing weekend does not give you a license to leave your insulin or inhalers behind.

Conclusion

There are very few high quality well designed studies in this field. My ‘yūgen’ (backed up by reading what little research we have available) suggests that there might just be something in ecotherapy that links to health. Unfortunately, it is hard to be more specific and say much more than that.

We really need more ecowarriors like Dr Li. He applied science and statistics to test out the validity of his ‘yūgen’ and published his findings in peer reviewed journals. His research (and passion) helped lift forest bathing from a metaphysical hobby to the status of forest medicine.

You can argue that this shift does not matter as many people were benefitting from forest bathing prior to Dr Li. Agreed but the reality is that more people in Japan can benefit safely from this practice now that it is accepted as forest medicine.

The best example of the type of research that we need comes from the myopia-vitamin D studies. Here, we saw a positive link between being outdoors and myopia protection. A logical assumption was that the vitamin D factor was at play. More detailed work and analysis showed the outdoors factor was not vitamin D. Very logical detective work.

As mentioned above, the key issue here is the fact that most of these studies show links and association between health and ecotherapy. This does not prove causation.

If our being outdoors improves our health, is it all to do with ‘being outdoors’? Could it have something to do with not being stationary, indoors and using technology? We cannot say for sure at this stage.

Regardless of the specific ‘why”, I am signing off, powering down and heading outdoors to spend some time in nature.