The effect of randomised exposure to different types of natural outdoor environments compared to exposure to an urban environment on people with indications of psychological distress in Catalonia.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 28248974 · doi:10.1371/journal.pone.0172200
What was done
A randomized crossover study in Catalonia evaluated 26 individuals with indications of psychological distress exposed in groups to green (Collserola Natural Park), blue (Castelldefels beach), and urban (Eixample neighbourhood) environments for 30 and 30+180 minutes between October 2013 and January 2014. Participants engaged in unconstrained normal activity during exposures. Mood (Total Mood Disturbance, TMD), attention capacity (backwards digit-span task), stress (salivary cortisol), blood pressure, heart rate, and heart rate variability (LF, HF, LF:HF ratio, and coefficient of component variance) were measured before, during, and after exposure. Potential mediators including air pollution, noise, physical activity, social interactions, and self-perceived restoration experience were also measured.
What was found
Compared with the urban environment, green exposure resulted in statistically significantly lower TMD [-4.78 (-7.77, -1.79) points difference] and lower salivary cortisol [-0.21 (-0.34, -0.08) log nmol/L]. Blue exposure resulted in statistically significantly lower TMD [-4.53 (-7.57, -1.49) points difference] and favorable changes in heart rate variability indicators (specifically LF:HF and CCV-LF:HF with approximately -0.20 points of difference). Physical activity and self-perceived restoration experience partially mediated the TMD improvements, while physical activity and air pollution partially mediated heart rate variability associations.
Why it matters
This study provides experimental evidence that real-world exposure to natural green and blue environments acutely alleviates mood disturbance and physiological stress markers in people with psychological distress.
Limits
The sample size was very small (n = 26), limiting statistical power and generalizability. Unconstrained group exposures may have introduced behavioral variations, and no long-term follow-up beyond the acute testing period was reported in the abstract.
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