The effects of walking in nature on negative and positive affect in adult psychiatric outpatients with major depressive disorder: A randomized-controlled study

Mood and physiological effects of visual stimulation with images of the natural environment in individuals with depressive and anxiety disorders

BACKGROUND

Nature therapies are gaining attention as non-pharmacological treatments for depressive and anxiety disorders, but research on their effectiveness in patients is limited. This study investigates the mood-improving effects of visual stimulation with natural environmental images in patients with depressive and anxiety disorders.

METHODS

We conducted a randomized crossover comparison trial involving 60 right-handed adult participants with depressive or anxiety disorders and receiving outpatient treatment. Visual stimuli of natural environments consisted of green-themed nature images, while the control stimuli featured urban scenes dominated by buildings. The stimulation lasted for 3 min, during which orbital prefrontal brain activity was measured using a 2-channel Near-infrared Spectroscopy (NIRS) system, and heart rate variability was assessed using fingertip accelerated plethysmography.

RESULTS

Mood enhancement effects were observed in both the depressive and anxiety disorder groups following visual stimulation with nature images. In the depression group, orbital prefrontal oxygenated hemoglobin concentration significantly increased after visual stimulation with nature images, while there were no significant changes in the anxiety group. However, in the anxiety group, a correlation was found between reduced orbital prefrontal oxygenated hemoglobin in response to nature images and increased mood-enhancement. Furthermore, the severity of depressive symptoms did not significantly affect the intervention effects, whereas heightened anxiety symptoms was associated with a smaller mood enhancement effect.

DISCUSSION

Our study demonstrates the benefits of nature image stimulation for patients with depressive and anxiety disorders. Differential orbital prefrontal brain activity impacts notwithstanding, both conditions exhibited mood enhancement, affirming the value of nature image stimulation.

Associations of nature contact with emotional ill-being and well-being: the role of emotion regulation

Nature contact has associations with emotional ill-being and well-being. However, the mechanisms underlying these associations are not fully understood. We hypothesised that increased adaptive and decreased maladaptive emotion regulation strategies would be a pathway linking nature contact to ill-being and well-being. Using data from a survey of 600 U.S.-based adults administered online in 2022, we conducted structural equation modelling to test our hypotheses. We found that (1) frequency of nature contact was significantly associated with lesser emotional ill-being and greater emotional well-being, (2) effective emotion regulation was significantly associated with lesser emotional ill-being and greater emotional well-being, and (3) the associations of higher frequency of nature contact with these benefits were partly explained via emotion regulation. Moreover, we found a nonlinear relationship for the associations of duration of nature contact with some outcomes, with a rise in benefits up to certain amounts of time, and a levelling off after these points. These findings support and extend previous work that demonstrates that the associations of nature contact with emotional ill-being and well-being may be partly explained by changes in emotion regulation.

Walking in nature may improve affect but not cognition

Beneficial effects of natural environments on affect have been consistently reported, but effects on cognition have been less consistent. We examined affect and cognitive performance in the domains of attention, working memory, executive function, and recall and recognition memory in a sample of 188 undergraduate participants who completed a walk in one of three environments: an outdoor nature environment, an outdoor urban environment, or an indoor (treadmill) environment. Supporting the hypotheses, the outdoor nature environment resulted in the greatest increase in positive affect and decrease in negative affect from pre-to post-walk. However, there were no effects of location on any cognitive measure. These results suggest that cognitive effects do not always occur in tandem with affective benefits. Possible explanations, including prior frequent exposure to nature in our participants and extremity of the natural environment, are discussed.

Association between greenspace exposure and suicide-related outcomes across the lifespan: A systematic review

A growing number of studies have linked greenspace exposure to suicide, but findings are inconsistent. We conducted a systematic review on the associations between greenspace exposure and suicide-related outcomes (namely, suicide mortality, self-harm, and suicidal ideation) up until January 6, 2023. We used the Mixed Methods Appraisal Tool (or MMAT) to assess the quality of the included studies. In total, 23 studies met our inclusion criteria, consisting of 14 ecological, four cross-sectional, three longitudinal, and two experimental studies. Most studies were published in 2022 and conducted in Europe (n = 10), Asia (n = 7), and North America (n = 5), with one worldwide analysis. Various indicators were used to assess greenspace exposure including objective measures (e.g., level of surrounding greenness, quantity, structural features, tree canopy coverage), and greenspace use (e.g., duration and frequency). Suicide mortality was the most studied outcome (n = 14). Quality assessment showed that most (87 %) of the included observational studies used representative samples. Protective associations of exposure to greenspace were reported for suicide mortality (9/14 or 64 %), self-harm (n = 3/5 or 60 %) and suicidal ideation (n = 4/6 or 67 %), with nine or 36 % studies reporting no association. Most of the included studies adjusted for key covariates such as age, sex, and socioeconomic status at various aggregate levels (e.g., household, city). For greenspace exposure and suicide mortality, studies stratified by sex (n = 10) showed larger protective associations for females (n = 7) than for males (n = 4). However, the included studies showed high heterogeneity in terms of exposure indicators and greenspace definitions. Experimental studies and studies using youth samples were rare. While more research is warranted, preliminary findings suggest protective associations between greenspace exposure and suicide-related outcomes.

Testing the causal relationships of physical activity and sedentary behaviour with mental health and substance use disorders: a Mendelian randomisation study

Observational studies suggest that physical activity can reduce the risk of mental health and substance use disorders. However, it is unclear whether this relationship is causal or explained by confounding bias (e.g., common underlying causes or reverse causality). We investigated the bidirectional causal relationship of physical activity (PA) and sedentary behaviour (SB) with ten mental health and substance use disorders, applying two-sample Mendelian Randomisation (MR). Genetic instruments for the exposures and outcomes were derived from the largest available, non-overlapping genome-wide association studies (GWAS). Summary-level data for objectively assessed PA (accelerometer-based average activity, moderate activity, and walking) and SB and self-reported moderate-to-vigorous PA were obtained from the UK Biobank. Data for mental health/substance use disorders were obtained from the Psychiatric Genomics Consortium and the GWAS and Sequencing Consortium of Alcohol and Nicotine Use. MR estimates were combined using inverse variance weighted meta-analysis (IVW). Sensitivity analyses were conducted to assess the robustness of the results. Accelerometer-based average PA was associated with a lower risk of depression (b = -0.043, 95% CI: -0.071 to -0.016, effect size[OR] = 0.957) and cigarette smoking (b = -0.026; 95% CI: -0.035 to -0.017, effect size[β] = -0.022). Accelerometer-based SB decreased the risk of anorexia (b = -0.341, 95% CI: -0.530 to -0.152, effect size[OR] = 0.711) and schizophrenia (b = -0.230; 95% CI: -0.285 to -0.175, effect size[OR] = 0.795). However, we found evidence of reverse causality in the relationship between SB and schizophrenia. Further, PTSD, bipolar disorder, anorexia, and ADHD were all associated with increased PA. This study provides evidence consistent with a causal protective effect of objectively assessed but not self-reported PA on reduced depression and cigarette smoking. Objectively assessed SB had a protective relationship with anorexia. Enhancing PA may be an effective intervention strategy to reduce depressive symptoms and addictive behaviours, while promoting sedentary or light physical activities may help to reduce the risk of anorexia in at-risk individuals.

Protocol for the Open Sky School: a two-arm clustered randomized controlled trial to test the effectiveness of a nature-based intervention on mental health of elementary school children

BACKGROUND

This article outlines the protocol for a trial to test the effectiveness of a nature-based intervention called Open Sky School to reduce mental health problems among elementary school children. Experimental studies show that contact with nature (e.g. walks in parks) improve mental health. A growing number of teachers have been applying outdoor education within the regular school curriculum and evidence suggests that such teaching methods could improve students' mental health but a randomized controlled trial has never been conducted.

METHODS

A two-arm clustered randomized controlled trial will be conducted in elementary schools across Québec, Canada. Following informed consent by teachers, parents and students, schools will be randomly assigned 1:1 to the intervention or the control group with a total of 2500 5-6^th grade students and 100 teachers expected to participate. The intervention will take place outdoors in a green-space (2 h per week for 12 weeks) and include a toolkit of 30 activities to foster well-being (e.g. mindfulness) and academic competencies (e.g. mathematics). Questionnaires will be administered to teachers and students before, immediately after and 3 months after the intervention. The primary outcome will be reductions of mental health problems in children from pre-to-post test (Social Behavior Questionnaire: self and teacher reports). Secondary outcomes include depression, positive and negative affect, nature connectedness, and pro-environmental behaviors among children. We will explore, immediate benefits on teacher's well-being and positive and negative affect and sustained benefits among students at 3 months follow-up. For the primary outcome, we will explore moderators including child's sex, child's disability status, the green-space of neighbourhoods, the school's socio-economic position and teacher's experience.

DISCUSSION

In conducting the first randomized controlled trial of the Open Sky School, our results could provide empirical evidence on the effectiveness of nature-based interventions in reducing mental health problems among elementary school children.

TRIAL REGISTRATION

This study was registered with clinicaltrials.gov: NCT05662436 on December 22, 2022.