The positive impacts of spending time in nature are well-established, but just much time and which type of exposure will help you reap maximum benefits? A research team from the University of Michigan recently published the results of a study to determine how the duration and type of nature experiences impact two physiological biomarkers of stress.
In a statement to Science Daily Dr. MaryCarol Hunter—lead author and associate professor at the University of Michigan—summarized that the “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.”
Over eight weeks, study participants from urban settings were instructed to have a “nature experience” of at least 10 minutes or more at least three times a week. Participants were able to choose the time, duration, and place of their nature experiences according to their personal schedules and preferences.
Researchers analyzed salivary cortisol and alpha-amylase to determine the impact of the nature experience. Elevated cortisol levels have a myriad of effects, including interference with learning and memory, lower immunity function, increased blood pressure and weight, and heart disease. Salivary alpha-amylase is produced by the digestive system and responds to physical and physiological stressors.
Throughout the study, saliva samples were taken before and after four selected nature experiences. Analysis of the stress biomarkers in the saliva samples demonstrated a reduction in stress after a 20-30-minute nature experience; cortisol levels reduced by 21.3% per hour and alpha-amylase dropped by 28.1% per hour. The biomarker levels continued to decline after the nature experience, but at decreased rates. Amylase levels only dropped for the least active sitting or sitting-walking participants. The type of activity did not impact cortisol levels.
According to the study, some healthcare providers have started to write nature prescriptions, which are also referred to as “nature pills.” Studies such as this help healthcare providers determine the parameters of a nature pill to best support their patients’ needs. For future nature pill research, the team recommends a larger sample size, a broader range of nature experiences, and duration times below 10 minutes and over 30 minutes.