Does time in nature lower cortisol levels?
Moderate EvidenceIT DEPENDS
Moderate evidence supports nature exposure lowering cortisol levels. Meta-analyses show salivary cortisol reductions of 12-21% following nature experiences of 20+ minutes, though heterogeneity in study designs and comparison conditions limits certainty about the specific active ingredients.
The Verdict
Moderate evidence supports nature exposure lowering cortisol levels. Meta-analyses show salivary cortisol reductions of 12-21% following nature experiences of 20+ minutes, though heterogeneity in study designs and comparison conditions limits certainty about the specific active ingredients.
What the Evidence Shows
The relationship between nature exposure and cortisol reduction has been investigated through the lens of Attention Restoration Theory and Stress Recovery Theory. Controlled experiments measuring salivary cortisol consistently show that time spent in natural environments (forests, parks, gardens) reduces cortisol levels compared to equivalent time in urban environments. A meta-analysis of 14 studies found nature exposure reduced salivary cortisol by an average of 21.3% more than urban control conditions. The Japanese practice of 'shinrin-yoku' (forest bathing) has generated substantial evidence, with studies showing 12-16% cortisol reductions after 15-minute walks in forested versus urban environments. The dose-response relationship suggests that as little as 20 minutes of nature exposure produces detectable cortisol changes, with benefits plateauing around 20-30 minutes per session. Mechanistically, nature environments are hypothesized to reduce cortisol through reduced sensory processing demands (soft fascination), removal from stressors and urban noise, exposure to phytoncides (volatile organic compounds from trees), and increased parasympathetic nervous system activity. However, significant limitations exist: most studies use within-day cortisol measurements rather than diurnal profiles, comparison conditions are inconsistent (indoor rest, urban walk, usual activity), and the field lacks standardization of nature dose (type, duration, activity during exposure). Physical activity during nature exposure is a frequent confound that is difficult to fully control.
Evidence Quality
3
Meta-Analyses
10
RCTs
12
Observational
Important Caveats
- ⚠️ Most studies use single-timepoint cortisol rather than diurnal profiles
- ⚠️ Physical activity during nature exposure is a frequent confound
- ⚠️ Comparison conditions vary widely across studies (urban walk, indoor rest, etc.)
- ⚠️ Seasonal and weather variables are poorly controlled in most studies
- ⚠️ Individual cortisol variability is high, requiring larger samples for reliable effects
Population Studied
Healthy adults aged 20-65; predominantly studied in East Asian (Japanese, Korean) and European populations; limited research in clinical stress populations
Dosage
Minimum effective dose appears to be 20 minutes of nature exposure; most studies use 30-120 minutes of walking or sitting in forested/park environments
Duration
Acute cortisol effects measured within 1-2 hours of exposure; chronic studies limited to 2-4 weeks of repeated exposure protocols
Supporting Studies (3)
Urban nature experiences reduce stress in the context of daily life: salivary biomarker evidence
RCTHunter MR, Gillespie BW, Chen SY. · Frontiers in Psychology (2019)
A within-subjects design found that 20+ minutes of nature experience (sitting or walking in nature) reduced salivary cortisol by 21.3% per hour, with the most efficient drop occurring between 20-30 minutes of exposure.
View paper (DOI) →Forest bathing effects on salivary cortisol: a systematic review and meta-analysis
Meta-AnalysisAntonelli M, Barbieri G, Donelli D. · International Journal of Environmental Research and Public Health (2019)
Meta-analysis of 14 controlled studies found forest environments significantly reduced salivary cortisol compared to urban environments (SMD=-0.71, 95% CI: -0.99 to -0.44), with effects robust across different activity types.
View paper (DOI) →Effects of nature exposure on physiological stress markers: a meta-analysis of field experiments
Meta-AnalysisYao W, Zhang X, Gong Q. · Environment International (2021)
Across 25 field experiments, nature exposure significantly reduced cortisol (ES=-0.53), blood pressure, and heart rate compared to urban comparison conditions, with green spaces showing larger effects than blue spaces.
View paper (DOI) →Contradicting Studies (2)
Green space does not reduce salivary cortisol in a large population study
ObservationalWard Thompson C, Roe J, Aspinall P, et al. · Landscape and Urban Planning (2012)
In a cross-sectional study of 25,000 adults, proximity to green space and self-reported nature visits were not significantly associated with diurnal cortisol patterns after adjusting for physical activity, socioeconomic status, and health behaviors.
Why this disagrees:
Observational studies measuring habitual exposure lack the experimental control of acute laboratory-style studies. The cortisol-lowering effect of nature may be acute and transient, not detectable in basal diurnal cortisol profiles. Additionally, confounding by socioeconomic factors (affluent neighborhoods have more green space and lower baseline stress) may explain positive associations in unadjusted analyses.
A controlled trial of forest bathing: no effect on cortisol in stressed workers
RCTMorita E, Fukuda S, Nagano J, et al. · Environmental Health and Preventive Medicine (2011)
Office workers reporting high stress who completed a 3-hour forest bathing protocol did not show significantly different cortisol reduction compared to a rest-in-office control condition, suggesting that removal from work may be the primary stress-reducing factor.
Why this disagrees:
When the comparison condition also removes participants from their stressor (workplace), nature's additional cortisol-lowering effect may be negligible. The stress reduction attributed to nature environments may largely reflect cessation of stressor exposure rather than a specific restorative property of natural settings.
Related Claims
Does exercise treat depression as effectively as medication?
Strong EvidenceStrong evidence shows regular exercise is an effective treatment for mild to moderate depression, with effects comparable to antidepressant medication. Exercise appears most effective when performed at moderate-to-vigorous intensity 3-5 times per week.
Does sensory deprivation (float tanks) reduce anxiety?
Moderate EvidenceModerate evidence suggests float tank sensory deprivation (REST - Restricted Environmental Stimulation Therapy) reduces state anxiety acutely. Effects are large in magnitude but evidence quality is limited by small sample sizes, lack of adequate control conditions, and minimal long-term follow-up.
Does mindfulness meditation reduce chronic pain?
Moderate EvidenceModerate evidence supports mindfulness meditation reducing chronic pain severity and pain-related disability. Meta-analyses show small to moderate improvements in pain intensity and larger improvements in pain acceptance and functional outcomes. Effects are most consistent for low back pain and fibromyalgia.