The science

The Library

The practices at Halcyon are old. The research on them is newer, and growing. These are the studies we read and return to, each with a short note in plain language and a link to the original paper. We share them to inform, not to promise, and none of it is medical advice.

6 studies

Nature immersion

Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis

Antonelli M, Barbieri G, Donelli D

International Journal of Biometeorology · 2019

This systematic review and meta-analysis looked at whether forest bathing (shinrin-yoku) lowers cortisol, a commonly used stress hormone marker. From 971 screened articles, 22 studies were included in the review and 8 in the statistical meta-analysis. In all but two of the included studies, cortisol was lower after time in the forest compared with control or urban groups, or dropped from before to after the forest session. The pooled analysis found salivary cortisol was lower in forest groups than urban groups. The authors conclude that forest bathing can influence cortisol in the short term in a way that suggests lower stress, while noting that people's expectations, a placebo effect, may play an important role. They also point to the limited amount of available data as a reason for more research.

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Nature immersion · Guided Hike

Nature experience reduces rumination and subgenual prefrontal cortex activation

Bratman GN, Hamilton JP, Hahn KS, et al.

Proceedings of the National Academy of Sciences · 2015

Rumination, the habit of repetitive negative thinking about oneself, is linked to higher risk of depression. In this study published in PNAS, healthy participants took a 90-minute walk either in a natural setting or in an urban setting. Those who walked in nature showed reduced self-reported rumination and reduced activity in the subgenual prefrontal cortex, a brain area associated with rumination, as measured by brain imaging. Those who walked along a busy urban route showed no such changes. The authors suggest this may be one pathway by which nature experience supports mental well-being, and that accessible natural areas could be an important mental health resource. One limitation is that the abstract does not report a large sample, and the participants were healthy adults, so the effect in people with depression is not tested here.

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Nature immersion · Guided Hike

Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review

Hansen MM, Jones R, Tocchini K

International Journal of Environmental Research and Public Health · 2017

Shinrin-yoku, or forest bathing, is the Japanese practice of spending mindful time among trees. This state-of-the-art review set out to gather empirical research on its physical and psychological effects, much of it from Japan and China, and to encourage longitudinal research in Western countries. Searching five databases, the authors started with 127 papers and included 64 studies published between 2007 and 2017, grouping them into physiological, psychological, sensory and framework studies. They conclude that the human health benefits of immersion in nature continue to be actively researched and suggest nature therapy as a possible health promotion approach for modern stress, including technology-related stress. The limitation is that this is a narrative review: it summarizes research but does not pool results or rate how strong each study was.

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Nature immersion

Outdoor blue spaces, human health and well-being: A systematic review of quantitative studies

Gascon M, Zijlema W, Vert C, et al.

International Journal of Hygiene and Environmental Health · 2017

Blue spaces are outdoor water environments such as lakes, rivers and the sea. This systematic review gathered 35 quantitative studies on how exposure to blue space, whether near home or while visiting, relates to human health and well-being; most studies were rated as good quality. The balance of evidence suggested a positive link between more blue space exposure and better mental health and well-being (12 studies) and higher levels of physical activity (13 studies). Evidence for links with general health, obesity and heart health was less consistent. The authors call the findings encouraging but point to clear limitations: relatively few studies, wide variation in how exposure and outcomes were measured, and mostly observational designs that cannot establish cause and effect.

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Nature immersion · Guided Hike

Spending at least 120 minutes a week in nature is associated with good health and wellbeing

White MP, Alcock I, Grellier J, et al.

Scientific Reports · 2019

Using a nationally representative survey of 19,806 people in England, researchers examined whether the amount of recreational time spent in nature during the previous week was linked to self-reported health and well-being. Compared with people who had no nature contact that week, those who spent at least 120 minutes in nature were significantly more likely to report good health and high well-being. Benefits peaked at around 200 to 300 minutes a week, with no further gain beyond that. The pattern held across groups, including older adults and people with long-term health conditions, and it did not matter whether the time came from one long visit or several shorter ones. The key limitation is that this was a cross-sectional survey, so it shows an association, not that nature time caused better health.

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Sound Bath · Nature immersion

The Effect of Music on the Human Stress Response

Thoma MV, La Marca R, Brönnimann R, et al.

PLoS ONE · 2013

Sixty healthy women with an average age of 25 were randomly assigned to one of three conditions before a standardized stress test: listening to relaxing choral music (Allegri's Miserere), listening to the sound of rippling water, or resting in silence. Researchers measured cortisol, salivary alpha-amylase, heart rate, heart rate variability, perceived stress and anxiety. Surprisingly, cortisol response to the stressor was highest in the music group and lowest in the rippling water group. However, after the stressor, the music group's alpha-amylase, a marker of the autonomic nervous system, returned to baseline faster than the silent rest group. Heart rate and self-reported stress did not differ between groups. Limitations: the sample was small and included only young women, and the results were mixed rather than pointing in one direction.

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