Leaf rustling, budding green and the scent of pine needles: In the spring, many people are attracted to the forest. Just a short walk there can reduce stress significantly, as a study by the University of Michigan shows. Accordingly, 20 minutes in the open will be enough to noticeably reduce the level of stress hormones. The researchers therefore speak in the journal "Frontiers in Psychology" of a "natural pill".
"We already know that it reduces stress when you spend time in nature," says ecologist and lead author of the study, Mary Carol Hunter. "So far it has been unclear how long and how often one should go into nature and also what kind of natural experience benefits us."
At least ten minutes in the countryside
The current research has shown that as little as 20 to 30 minutes in an environment that gives you a sense of nature suffices to effectively lower cortisol levels in the body. Cortisol, also known as stress hormone, is produced in the adrenal cortex and broken down in the liver. Permanently elevated cortisol levels, such as chronic stress, can lead to obesity, weaken the immune system, and promote cardiovascular disorders, depression and a host of other conditions.
The scientists at the University of Michigan had prescribed a regular "natural pill" to a group of 36 volunteers, including 33 women and three men: The subjects should undertake at least three walks a week in nature with a duration of ten minutes or more. Before and after the experiments, the participants took a saliva sample which was examined for both the cortisol levels and the so-called alpha-amylase. This enzyme is derived from the digestive tract and is known to give the body increased levels of stress.
Because the biomarkers change physiologically with the time of day, these daily fluctuations were taken into account in the calculation. The subjects were also allowed 30 minutes before they took the saliva sample, not eat or drink, as food in particular can greatly influence the alpha-amylase.
more on the subject
The volunteers were able to determine the day, duration and location of their natural experience to suit their individual lifestyle. However, they had to minimize some stress factors: "They should take the" nature pill "in the light of day, do no exercise and avoid social media, the Internet, phone calls, conversation and reading," says Hunter.
Forest walks as a therapy
After just 20 minutes of experiencing nature, the cortisol levels had dropped significantly in the subjects. The stress hormone was reduced most when participants spent about 20 to 30 minutes sitting or walking in the countryside. The participants stayed even longer in the open air, the cortisol continued to decrease, but not as strong as in the first 20 minutes. In alpha-amylase, the difference was clearly measurable only in those subjects who barely moved while out in the open, sitting on a bench, for example.
The researchers now hope that their experiment underlines the effectiveness of the "natural pill". They see outdoor living as a cost-effective therapeutic tool to contain the negative effects of city life, such as spending time indoors and in front of screens. "Physicians could use our findings as an evidence-based rule of thumb for what to prescribe in a natural pill," Hunter concludes.
More trees, less heart attacks?
The data are part of a growing body of research that confirms the positive effects of staying in nature or especially on a walk in the forest. As early as 1984, the Swedish researcher Roger Ulrich stated that the mere sight of trees could have a positive effect: patients who looked out of the hospital window for surgery after an operation needed less painkillers and recovered faster.
A Japanese study found that regular and extensive forest walks increased the number of natural killer cells, a subset of white blood cells, and part of the human immune system.
In 2015, American environmental psychologist Marc Berman added that the number of trees in a residential area is affecting the health of the residents. Those who lived in greener areas suffered less often from cardiovascular disease or diabetes. In their study, scientists tried to figure out that other factors also affect health. These include a higher socioeconomic status that allows people to move to the countryside, often accompanied by healthier diets and more exercise.
Forest medicine as a research branch
In Japan, the "Shinrin-yoku", ie the "bathing in the forest", even part of the state health care, "forest medicine" is since 2012 a separate branch of research at Japanese universities. Here is also explored, which factors provide exactly for the positive health effects. So it is still unclear whether it is due to the air of the forest or the special vegetation.
Does it make any difference whether you are walking through a Japanese or German forest? At least since 2017, the self-experiment can be done on Usedom: Here is the first certified spa and healing forest in Germany, which the operator also referred to as "natural pharmacy".