Stress reduction through contact with nature is well established, but far less is known
about the contribution of contact parameters – duration, frequency, and nature quality.
This study describes the relationship between duration of a nature experience (NE), and
changes in two physiological biomarkers of stress – salivary cortisol and alpha-amylase.
It is the first study to employ long-term, repeated-measure assessment and the first
evaluation wherein study participants are free to choose the time of day, duration, and
the place of a NE in response to personal preference and changing daily schedules.
During an 8-week study period, 36 urban dwellers were asked to have a NE, defined as
spending time in an outdoor place that brings a sense of contact with nature, at least
three times a week for a duration of 10 min or more. Their goal was compliance within
the context of unpredictable opportunity for taking a nature pill. Participants provided
saliva samples before and after a NE at four points over the study period. Before-NE
samples established the diurnal trajectory of each stress indicator and these were in line
with published outcomes of more closely controlled experiments. For salivary cortisol,
an NE produced a 21.3%/hour drop beyond that of the hormone’s 11.7% diurnal drop.
The efficiency of a nature pill per time expended was greatest between 20 and 30 min,
after which benefits continued to accrue, but at a reduced rate. For salivary alphaamylase,
there was a 28.1%/h drop after adjusting for its diurnal rise of 3.5%/h, but
only for participants that were least active sitting or sitting with some walking. Activity
type did not influence cortisol response. The methods for this adaptive management
study of nature-based restoration break new ground in addressing some complexities
of measuring an effective nature dose in the context of normal daily life, while bypassing
the limitations of a clinical pharmacology dose–response study. The results provide a
validated starting point for healthcare practitioners prescribing a nature pill to those
in their care. This line of inquiry is timely in light of expanding urbanization and rising
School for Environment and Sustainability, University of Michigan, Ann Arbor, MI, United States
Copyright: Copyright © 2019 Hunter, Gillespie and Chen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).