In recent years, particularly in Japan, spending time in forests has become the wellness trend du jour. A recent meta-analysis investigates whether so-called forest bathing really can significantly reduce levels of stress. Share on Pinterest The authors of a recent meta-analysis ask whether forest bathing can reduce stress levels. Forest bathing — a translation of the Japanese term shinrin yoku — is not a new idea, of course; ramblers have enjoyed forest walks for generations. However, in 1982, the Japanese Ministry of Agriculture, Forestry, and Fisheries first coined the term shinrin yoku. The act goes beyond walking through nature, according to experts who explain that shinrin yoku “can be defined as making contact with and taking in the atmosphere of the forest.” The primary benefit that proponents assign to forest bathing is a reduction in stress levels. However, others go even further. For instance, the authors of a 2017 review concluded that “forest therapy is an emerging and effective intervention for decreasing adults’ depression levels.” Other researchers have investigated whether forest bathing might also help prevent lung and heart disease.

The power of nature Aside from forest bathing, the psychological benefits of being around green spaces, in general, are also receiving growing attention from scientists. Similarly, there is some evidence, although it is low-quality, that exercising in natural environments, as opposed to indoors, improves mental well-being. Weaving these threads together, it seems that the overall effect of nature on our mental health is a topic worthy of study. Recently, a group of researchers from Italy set out to develop a clearer picture of forest bathing’s effect on stress levels. They published their findings in the International Journal of Biometeorology. The team designed a review and meta-analysis of relevant studies, focusing on levels of cortisol as a biomarker for stress. Cortisol is a steroid hormone, the production of which increases during times of stress. It is possible to measure these increases in samples of saliva or serum, making it a relatively easy way to assess an individual’s levels of psychological stress at any given time. The authors screened almost 1,000 articles but selected only 22 to include in their systematic review and eight to use in their meta-analysis.

Reviewing forest bathing The authors explain that for their analysis, forest bathing “was defined as staying in a forest, either walking or simply resting and watching it, and taking in its air for a specified amount of time.” Some of the studies that the scientists included used a control group where there was no intervention, while others compared forest bathing with other activities, such as walking through an urban area. The authors found that all but two of the studies reported a benefit: Cortisol levels were significantly lower in the forest group compared with the control or comparison group. The authors also noticed an “anticipatory effect” of shinrin yoku — individuals experienced a drop in cortisol just before beginning their forest session. For instance, in one study, participants’ cortisol levels dropped once the researchers had informed them that they were going to take part in forest bathing. The authors explain: “Forest bathing is considered an anti-stress practice, and planning to visit a forest seems to positively influence cortisol levels, even before physically interacting with it; therefore, watching a forest, and possibly even the sole mental visualization of a forest, may have a role in triggering anticipated placebo effects.” Although scientists do not fully understand the placebo effect, they know that it is powerful.