Background - The Generalised Unsafety Theory of Stress, a novel stress explanation, considers the stress response as a default mode of the body, which is always active independently from stressors...Show moreBackground - The Generalised Unsafety Theory of Stress, a novel stress explanation, considers the stress response as a default mode of the body, which is always active independently from stressors unless it is inhibited based on perceiving safety. GUTS suggests there are compromised domains where stress is chronically released despite a lack of clear stressors, and the organism is unable to inhibit the stress mechanism mostly because of perceiving generalised unsafety around. One of these compromised domains is believed to be urban environments as they cannot provide sufficient signs of safety, and they mainly consist property of strangers. Natural environments in contrast are believed to provide signs of safety and therefore decrease stress levels. Using meta-analysis, this current research aimed to find and summarize evidence from existing studies reporting that urban environments are associated with increased levels of stress, Method - In total, 12 studies, collected from Web of Science database, were included in six meta-analyses conducted on heart rate variability (high frequency, low frequency/high frequency), saliva cortisol, blood pressure (systolic and diastolic), and heart rate data of healthy adult participants during and after exposure to urban and natural environments. Results - Statistically significant increased heart rate was found after a walk in the urban environment (g = 0.37, 95% CI: 0.20; 0.50, p <0.0001). High frequency heart rate variability was significantly lower after an urban walk(unknown baseline balance group: g = -0.33, 95% CI: -0.55; -0.11; baseline balanced: g = -2.52, 95% CI: -3.25; -1.78). Low frequency heart rate variability was significantly higher during the urban walk (unknown baseline balance group: g = 0.33, 95% CI: 0.49; 1.80; baseline balanced: g = 2.52, 95% CI: 1.78; 3.26). Subgroup analyses and funnel plots for heart rate variability showed a possible small-study effect in the baseline balanced groups. Blood pressure and cortisol measurements showed no significant effect and were ambiguous because of high heterogeneity and small number of included studies. Conclusions - Heart rate variability and heart rate measures indicated a higher stress level in urban than in natural environments providing an example of prolonged stress without stressors, explainable by GUTS. For blood pressure and cortisol no such evidence was provided. However, the results should be carefully interpreted because of high between-study heterogeneity and other limitations of these studies. Further research into stress measurements and effects of natural and urban environment on stress are required to provide reliable evidence.Show less
