For the first time, researchers have been able to measure the therapeutic effect of experiencing the outdoors. The study has revealed that walking or sitting among nature for at least 20 minutes can significantly reduce stress hormone levels. The finding will enable healthcare practitioners to prescribe “nature pills” to relieve symptoms of stress.
Study lead author Dr. MaryCarol Hunter is an associate professor in the School for Environment and Sustainability at the University of Michigan.
“We know that spending time in nature reduces stress, but until now it was unclear how much is enough, how often to do it, or even what kind of nature experience will benefit us,” explained Dr. Hunter. “Our study shows that for the greatest payoff, in terms of efficiently lowering levels of the stress hormone cortisol, you should spend 20 to 30 minutes sitting or walking in a place that provides you with a sense of nature.”
A prescription of nature pills could be a low-cost solution to address the negative health impacts that are associated with indoor and urban lifestyles. Dr. Hunter and her team designed an experiment to determine what would be an effective dose of nature.
Individuals who volunteered in the study were instructed to spend 10 minutes or longer in nature at least three times a week for eight weeks. Levels of the stress hormone cortisol were measured in saliva samples collected before and after the participants had a dose of nature on four separate occasions.
“Participants were free to choose the time of day, duration, and the place of their nature experience, which was defined as anywhere outside that in the opinion of the participant, made them feel like they’ve interacted with nature. There were a few constraints to minimize factors known to influence stress: take the nature pill in daylight, no aerobic exercise, and avoid the use of social media, internet, phone calls, conversations and reading,” said Dr. Hunter.
“Building personal flexibility into the experiment, allowed us to identify the optimal duration of a nature pill, no matter when or where it is taken, and under the normal circumstances of modern life, with its unpredictability and hectic scheduling.”
According to the study, a twenty-minute nature experience was enough to significantly reduce cortisol levels. Between 20 and 30 minutes in nature, however, produced the greatest drop in cortisol levels. Beyond 30 minutes, the benefits continued to accumulate, but at a slower rate.
“Healthcare practitioners can use our results as an evidence-based rule of thumb on what to put in a nature-pill prescription,” said Dr. Hunter. “It provides the first estimates of how nature experiences impact stress levels in the context of normal daily life. It breaks new ground by addressing some of the complexities of measuring an effective nature dose.”
The study is published in the journal Frontiers in Psychology.