The effect of exposure to the natural environment on stress reduction: A meta-analysis

There is an increasing evidence that natural environment provides substantial human health benefits. One mechanism underlying this relationship is the experience of stress. However, no formal statistical assessment has been conducted to test this statement. A meta-analysis was used in our study to conduct a comprehensive systematic review for the effect of direct exposure to natural environment on stress relieving. We searched four online databases and reference lists, 31 studies with a total of 1842 participants were included. Meta-analysis results showed increased natural exposure was associated with decreased salivary cortisol -0.06 (95 % CI -0.08, -0.04), state-of anxiety -12.48 (95 %CI -26.61, 1.66), self-reported stress -0.33 (95 %CI -0.78, 0.13), systolic blood pressure (SBP) -3.82 (95 %CI -6.77, -0.86), diastolic blood pressure (DBP) -2.21 (95 %CI -3.93, -0.49), Ln(LF/HF) -0.29 (95 %CI -0.41, -0.18) of heart rate variability (HRV) and increased restorative outcomes 4.82 (95 %CI -1.87, 11.51). These measurements provide the most convincing evidence that exposure to the natural environment can lead to stress reduction, and ultimately improve health. However, there was significant residual heterogeneity between studies and risk of bias was high. It is a recommended that future research in this area take appropriate steps to reduce bias and improve quality in order to build a strong evidence-based medicine foundation. This will help to convince policymakers and health professionals of the stress relieving benefits of exposure to nature, and encourage to give due regard to create, maintain, and improve existing accessible greenspaces in insufficient areas.