The concept of forest bathing, or shinrin yoku, has gotten a lot of attention in the last few years, as research has suggested that it really does seem to confer health benefits, both mental and physical. A new study in from the University of Exeter tries to home in on how much nature we ought to take in, and finds that 120 minutes seems to be a threshold—but spending more than this amount of time is at least as good for us, too.
The study was published this week in Scientific Reports.
The researchers looked at data from almost 20,000 people in England, and correlated the time they said they spent in nature—whether in urban green spaces, actual forests, or the beach—with their physical and mental well-being. Spending 119 minutes or less didn’t seem to matter much, but people who got at least 120 minutes/week of nature were more likely to say they were in good health and had greater well-being. More than this amount also helped (i.e., people who got five hours were also in better health/well-being), so don’t think that two hours/week is an optimal dose—it’s just the minimum amount that the authors say showed a clear effect.
And interestingly, it didn’t seem to matter whether the “dose” was taken in one bout or broken up throughout the week. Nature’s effect seems to be cumulative.
“We tentatively suggest, therefore, that 120 mins contact with nature per week may reflect a kind of ‘threshold’, below which there is insufficient contact to produce significant benefits to health and well-being, but above which such benefits become manifest,” the authors write in their piece.
To put the benefit in perspective, the authors calculate that the health benefit of spending two hours per week in nature is comparable, among other things, to “achieving vs. not achieving recommended levels of physical activity in the last week.” The association probably doesn’t mean that we should swap exercise for sitting in a park for two hours, but just that the benefit to health is about the same. They point out that research into shinrin-yoku proper has found that there do seem to be discrete benefits of just being in nature without movement. (Getting ample exercise and spending time in nature is probably wise—all the better if you exercise in nature.)
Last year, a meta-analysis found that forest bathing was linked to reduced levels of the stress hormone cortisol, lower heart rate, reduced risk of coronary heart disease, lower blood pressure, lower cholesterol, reduced risk of type II diabetes, reduced all-cause mortality, and death from heart disease. Though some studies on the subject were omitted because of quality concerns, enough high-quality research, including a variety of countries and types of nature exposure, suggests that there may really be something to forest bathing.
The authors of that study suggested some interesting mechanisms, including the “old friends” hypothesis, whereby the additional exposure to pathogens we get from nature strengthens our immune systems (just as the lack of exposure, from over-use of antibacterial soap and fear about dirt in general, had lead to more health problems in recent decades). Another idea is that molecules emitted by trees, known as phytoncides, have antibacterial properties, and/or trigger the activity of cells in our own immune systems.
As the societal causes of poor health and mental health are becoming clearer, studies like this help bolster the movement toward prevention and behavior change. Spending time in nature, even if just at your local park, is definitely an important part of it. As the new study shows, aiming for a couple hours per week is probably good—getting more than this amount of nature into your life is almost certainly better.