Contact with nature is widely considered to ameliorate psychological stress, but the empirical support for a causal link is limited. We conducted a systematic review to synthesize and critically assess the evidence. Six electronic databases were searched. Twenty-six studies evaluated the difference between the effect of natural environments and that of a suitable control on the acute psychophysiological stress response. Eighteen studies were rated as being of moderate quality, four studies of low quality, and four studies of high quality. Meta-analyses indicated that seated relaxation (g = .5, p = .06) and walking (g = .3, p = .02) in natural environments enhanced heart rate variability more than the same activities in control conditions. Cortisol concentration measures were inconsistent. While intuitively and theoretically sound, the empirical support for acute stress-reducing effects of immersion in natural environments is tentative due to small sample sizes and methodological weaknesses in the studies. We provide guidelines for future research.

Existing research indicates that spending time in nature is associated with diverse aspects of children's health and wellbeing. Although fundamental to later life chances and health, no systematic reviews, to our knowledge, have focused specifically on the effects of interaction with nature on socioemotional functioning in childhood. Amongst children, what is the consistency of associations between the availability of or spending time in nature on socioemotional function and development? Furthermore, which child behaviours and states independently associate with socioemotional function and availability of or spending time in nature, and what is the consistency of associations between these behaviours and states and contact with nature? Embase, Environment Complete, MEDLINE, and APA PsycINFO. Eligible studies were backward and forward snowball-searched. Studies investigating effects of, or associations between, availability of or interaction with nature on socioemotional or proximal outcomes in children under the age of 12 years were included in this review. The internal validity of studies investigating socioemotional outcomes were based on assessments of elements of study design, conduct, and reporting to identify potential issues related to confounding or other biases. The number of analyses indicating positive, negative, and non-significant associations between availability or interaction with green space and the outcomes were summed. A total of 223 eligible full-texts, of which 43 pertained to socioemotional outcomes and 180 to proximal outcomes, met eligibility criteria. Positive associations between availability of and spending time in green space were found with children's intra- and interpersonal socioemotional function and development. Proportions of positive findings ranged from 13.9% to 55% across experimental and observational research, exposures, populations, and contexts. Modifying and mediating factors were identified. We found consistent evidence for improved aspects of cognition and, for children over six years, reduced risk of obesity and overweight in association with green space; consistent links between movement behaviours in the experimental, but not observational research; tentative trends suggesting associations with play, motor skills, language, screen time, and communication skills; little evidence for positive associations between green space and mood, physical wellbeing, and stress; some evidence for associations with healthy birth outcomes, and little evidence for direct associations between availability of green space and asthma and allergy prevalence, however, mediation via, for example, air pollution was likely. We identified few studies without either probable or severe risk of bias in at least one item. Improved study quality may therefore result in different results. Restricting analyses to include only studies considered at low risk of bias indicated similar or slightly lower proportions of positive findings. Risk of bias in proximal outcomes was not assessed. The empirical evidence for benefits of availability of and interaction green space for child socioemotional function and development must currently be considered limited. A number of proximal indicators were identified. Systematic review registration number. CRD42019135016.

In this systematic review, we summarized and evaluated the evidence for effects of, and associations between, immersive nature-experience on mental, physical, and social health promotion outcomes. Immersive nature-experience was operationalized as non-competitive activities, both sedentary and active, occurring in natural environments removed from everyday environments. We defined health according to the World Health Organization's holistic and positive definition of health and included steady-state, intermediate, and health promotion outcomes. An electronic search was performed for Danish, English, German, Norwegian, and Swedish articles published between January 2004 and May 2017. Manual approaches, e.g., bibliographies from experts, supplemented the literature search. Data were extracted from 461 publications that met the inclusion criteria. To assess the status and quality of the evidence for health promotion effects of immersive nature-experience, we focused on the subset of studies based on controlled designs (n = 133). Outcome level quality of the evidence was assessed narratively. Interventions most often involved adventure-based activities, short-termed walking, and seated relaxation in natural environments. We found positive effects on a range of health promotion outcomes grouped under psychological wellbeing (n = 97; ≈55% positive; ≈13% mixed; ≈29% non-significant; 2% negative); psychosocial function (n = 67; ≈61% positive; ≈9% mixed; ≈30% non-significant); psychophysiological stress response (n = 50; ≈58% positive; ≈18% mixed; ≈24% non-significant), and cognitive performance (n = 36; ≈58% positive; ≈6% mixed; ≈33% non-significant; 3% negative); and social skills and relationships (n = 34; ≈70% positive; ≈7% mixed; ≈22% non-significant). Findings related to outcomes categorized under physical health, e.g., risk of cardiovascular disease, were less consistent (n = 51; ≈37% positive; ≈28% mixed; ≈35% non-significant). Across the types of interventions and outcomes, the quality of the evidence was deemed low and occasionally moderate. In the review, we identify, discuss, and present possible solutions to four core methodological challenges associated with investigating immersive nature-experience and health outcomes: (1) intervention and program complexity; (2) feasibility and desirability of randomization; (3) blinding of participants and researchers; and (4) transferability and generalizability. The results of the review have been published as a popular-scientific report and a scientific research overview, both in Danish language.

Education outside the classroom (EOtC) has become an attractive approach, not only for learning but also for health. This explorative, cross-sectional study investigated children’s sedentary behaviours (SED), light physical activity (LPA) and moderate-to-vigorous PA (MVPA) on school days with an EOtC session in green space compared to school days with EOtC in other environments and without EOtC. Teachers from 17 Danish school classes practised EOtC for one school year on a weekly basis and self-reported the characteristics of the EOtC environment. The pupils’ PA was device-measured for seven consecutive days in a random period during the school year with AX3 accelerometers. Across 617 pupils (age 9–13 years), PA intensity cases (N = 2264) on school days (8:10–14:00 h) with (n = 317) or without (n = 1947) EOtC were included in a mixed-effects regression analysis. Mean exposure to EOtC was 262 min per session. School days with green EOtC (e.g., parks, forests and nature schools) were associated with (mean, [95% CI]) −24.3 [−41.8, −7.7] min SED and +21.3 [7.7, 36.4] min LPA compared to school days with non-green EOtC (e.g., cultural and societal institutions or companies) and with +6.2 [−0.11, 11.48] min MVPA compared to school days with a school-ground EOtC. No sex differences were found. In conclusion, school days with green EOtC must be considered promising to counteract children’s sedentary behaviours during school hours.