Human Health & Plants Research: Urban Nature Experiences Lower Physiological Indicators of Stress

Dr. Charles Guy

There is increasing evidence that both an active or passive nature experience (NE) can reduce psychological stress (PS), and provide other psychosocial therapeutic benefits. Yet how best to define and characterize PS remains a matter of debate. Cortisol is a prominent neuroendocrine hormone that is responsive to PS. In modern social media terms, cortisol levels are not only an indicator of PS it is an “influencer” of physiological stress responses. MaryCarol Hunter and colleagues (Hunter et al, 2019) designed and conducted a study to determine the effects of duration, frequency, and quality of nature experiences over a period of eight weeks from June to August on cortisol levels in a study population of 36 individuals of which 92% were female with an average age of 45.8 years. A second indicator of PS, salivary alpha amylase, was also evaluated in the study. However, significant challenges in determining whether a NE over time has modified the levels of cortisol and alpha amylase exists because their concentrations naturally vary over the course of a day. In the present study, participants were free to choose when and how to have a NE during the daylight hours. Participants collected saliva samples before and after every NE. The researchers then used the before NE samples to establish a daily profile of cortisol and alpha amylase levels. Based on the results of the experiment, Hunter and colleagues determined that salivary cortisol levels declined at a rate of 21.3%/hour following a NE compared to an average decline of 11.7%/hour without a NE. Similarly, there was a 28.1%/hour reduction following a NE in contrast to an average 3.5%/hour rise in salivary alpha amylase without a NE. A 21-30 minute nature experience most efficiently achieved the reductions in cortisol and alpha amylase. The results suggest that a NE can lower cortisol and alpha amylase by reducing psychological stress.

Hunter MR, Gillespie BW and Chen SY-P (2019) Urban nature experiences reduce stress in the context of daily life based on salivary biomarkers. Front. Psychol. 10:722. doi: 10.3389/psyg.2019.00722

Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida