The health benefits of nature are well-enough established that some healthcare providers prescribe it for their patients. Do these so-called "Nature Pills" work? If so, what is the dose?
This "nature pill" may be too big to swallow for most of us, especially on a regular basis—too remote, too much time required. Surely, more modest exposure to nature has health benefits. Is there a dose-response curve to nature? Photo: © Donald J. Rommes
The idea that exposure to nature has health benefits—especially mental health benefits—is well-supported by evidence. An increasing number of medical doctors are prescribing time in nature to their patients. It seems intuitive that this "nature pill"—as some have called it—should work, but is it supported by data? If so, is there a dose-dependent relationship?
In science, a randomized controlled trial (RCT) is the gold standard for determining the "true" answer to a question. In conducting a RCT on humans, two carefully matched populations of people are studied. One group of people will receive the intervention in question (the experimental group), the other will not (the control group). At the end of the study, the results are evaluated to see if the intervention resulted in a difference between the populations. The larger the numbers studied, the better matched the populations, the greater the effect (difference) seen, the more robust the statistical conclusion.
To draw meaningful conclusions, potential causes of bias should be eliminated. In addition to matching the groups as closely as possible, no one (neither the participants nor the conductors of the study) should know whether a study participant received or did not receive the intervention. In other words, everyone should be "blinded" to the intervention.
A RCT on the effect of a "nature pill" is impossible, because the participants cannot be blinded to the fact that that are being exposed to nature. But maybe there's a study that can approximate a RCT.
A 2019 study published in Frontiers of Psychology was designed to have each participant serve as their own control. After determining baseline measurements of two biochemical markers for stress at various times of the day, 36 urban dwellers were asked to have a nature experience (NE) of at least 10 minutes duration, three times a week. A (NE) was defined as spending time in an outdoor place that the participant felt brought a sense of contact with nature.
During the 8 week study, markers for stress (cortisol and amylase) were measured in saliva before and after the self-determined NE and the time of day was recorded.
The study determined that "taking a "nature pill" reduces stress by 21%/h (salivary cortisol) and 28%/h (salivary amylase). When the duration of the NE is between 20 and 30 min, the gain in benefit is most efficient.
This study differed from previous studies that looked at biological markers of stress to assess the impact of an exposure to nature. In the author's words, the approach was novel in several ways:
Results came from an experimental approach that can efficiently distinguish the contribution of a nature-based stress reduction from the concomitant diurnal change of a stress marker. In other words, the drop in a stress marker after a NE is real and not simply an artifact of normal diurnal variation.
Unlike previous studies, this one included repeated-measures testing of the same individuals over 2 months, allowing us to capture the realism of changing psychological and physiological states and reactions to changing environmental context for each participant. In other words, NE reduces stress over a spectrum of mental and physical states.
The experimental format is unique for nature restoration research in its use of an adaptive management design. Participants had significant control in how they “medicated” themselves in terms of when, where, and length of a NE. Self-medication works, but a dose of 20-30 minutes minimum is recommended.
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