Table 1.

Characteristics of included systematic reviews on greenspace and health with or without meta-analyses (36)

Author(Year)	Included Studies	Exposure(s)	Outcome(s)	Finding(s)
Bowler et al.20	25 studies (24 articles) including 13 crossover trials, 7 randomized controlled trials (RCTs), and 5 observational studies	Exposure group: walking or running in the natural environment, wilderness backpacking, gardening, passive/sedentary activities, or a mixture of activities Control group: outdoor built and non-green environment or indoor environment	Emotions (e.g., revitalization, anger, anxiety), attention, cardiovascular outcomes (e.g., blood pressure or pulse) hormone levels (salivary, urinary cortisol, amylase, and adrenaline), immune function, physical activity, motor performance, cerebral brain activity, engagement, memory recall, and sleep	Compared to a built environment, short-term exposure to natural environments was associated with better emotional states and attention (effect sizes ranged from 0.35 to 0.76), but not with other health outcomes.
van den Berg et al.21	40 studies (32 articles) including 34 cross-sectional studies and 6 longitudinal studies	Percentage of greenspace within a certain distance or radius around the residence, percentage of greenspace, greenspace percentage at the city level and county level, NDVI, and tree canopy coverage, distance to the nearest greenspace, number of different recreational or green qualities within a certain distance, and subjective measures of greenspace/naturalness	Perceived general health, perceived mental health, and all-cause mortality	There was evidence for positive associations between the quantity of greenspace and perceived mental health and all-cause mortality; there was moderate evidence for positive associations between greenspace and perceived general health. Despite these findings, the evidence was not convincing due to the lack of high-quality studies. Gender, age, and SES may modify the association between greenness and health, but the strength and direction of these effect modifiers is unclear.
de Keijzer et al.22	13 studies including 3 cohort studies, 2 ecological studies, and 8 cross-sectional studies	Percentage of greenspace and park area, greenness surrounding schools, homes, and commuting route between the two (using NDVI or tree counts) as well as ratings of greenness, self-reported or surveyed views of greenspace through the windows, and reporting of settings visited during activities	Cognitive development, cognitive function, cognitive decline or impairment, distraction and concentration problems, symptoms of inattention, measures of school performance, and dementia incidence	There was inadequate but suggestive evidence for a positive association between long-term greenspace exposure and cognitive functioning over the life course.
Kondo et al.23	68 studies including 14 with between-subjects designs, 3 case-control or case crossover studies, 9 quasi-experimental studies, 1 RCT, 30 longitudinal cohort studies, and 21 with within-subjects designs	Greenspace in residential area (e.g., NDVI, proximity to parks), greenspace in activity spaces (e.g., presence or absence of greenspace or park space), nature walk or run, greening intervention (e.g., neighborhood-level greenspace improvements, cleaned-and greened vacant lots), nature leisure experience, and residential relocation	Behavior (e.g., behavioral problems, smoking), birth outcomes (e.g., birth weight, preterm birth, small for gestational age), prostate cancer, cardiovascular diseases (e.g., autonomic function, blood pressure, CVD risk, dyslipidemia, etc.), metabolic (obesity, cortisol, diabetes, etc.), mortality, mental health (e.g., anger, anxiety, anxious, attention, etc.), violence-aggression, and respiratory diseases	There were positive associations between urban greenspace and attention, mood, and physical activity, as well as negative associations between greenspace and mortality, short-term cardiovascular markers and violence. No consistent associations were observed for the remaining outcomes.
Lambert et al.11	15 studies (11 articles) including 11 cohort studies, 1 cross-sectional studies, and 3 ecological studies	NDVI and street tree density	Asthma and allergic rhinitis	There was no significant association between residential greenness and asthma.
Houlden et al.28	52 studies including 6 longitudinal studies, 4 uncontrolled studies, 37 cross-sectional surveys	Amount of local-area greenspace, greenspace types, visits to greenspace, views of greenspace, greenspace accessibility, and subjective connectedness to nature	Mental wellbeing	There was adequate evidence for protective associations between local greenspace and life satisfaction but between local greenspace and personal flourishing. Evidence for associations between visits to greenspace, accessibility, types of greenspace, views of greenspace, and connectedness to nature were insufficient.
Lambert et al.25	5 papers including 11 different cohort studies	NDVI, proportion of tree canopy, land cover databases, and combination of high-resolution light detection and ranging (LiDAR), color infrared aerial imagery, and ancillary vector data.	Atopic sensitization	Protective effects of greenspace were reported in four cohorts; deleterious effects were reported in two cohorts; no significant associations were reported in another five cohorts.
Rautio et al.27	57 studies (11 on greenspace) including 43 cross-sectional studies and 14 longitudinal studies	Proportion of green area, presence of park, distance to parks, and proportion of greenspace, among others	Depressive mood	Built environments lacking greenspaces were related to depressive mood although the results were mixed.
Schulz et al.24	18 studies (4 on greenspace) including 14 cross-sectional studies and 4 longitudinal studies	Naturally or human-built areas (e.g., parks, forest, garden, and cemeteries) covered with grass, trees, shrubs, or other vegetation	Overall health, acute respiratory illness, chronic/allergic disease	Greenspace tended to be associated with acute respiratory symptoms but not with chronic respiratory conditions.
Twohig-Bennett and Jones4	143 studies including 103 observational and 40 interventional studies	Neighborhood greenspace (e.g., residential greenspace, street greenery, and tree canopy), greenspace-based interventions, proximity to large greenspace, comparisons between a green environment with an urban or indoor environment, and viewing trees through window, among others	Almost 100 outcomes including cardiovascular diseases (e.g., cardiovascular mortality, blood pressure, heart rate, and incidence of angina and myocardial infarction), pregnancy outcomes, self-reported health, mortality (e.g., all-cause, respiratory and intentional self-harm), and diabetes as well as various blood biomarkers (e.g., HDL-C, LDL-C, FBG, etc.)	Greenspace exposure was beneficially associated with a wide range of health outcomes including salivary cortisol, heart rate, diastolic blood pressure, high-density lipoprotein cholesterol, heart rate variability, preterm birth, type 2 diabetes, all-cause mortality, small size for gestational age, cardiovascular mortality, self-reported health, stroke, hypertension, dyslipidemia, asthma, and coronary heart diseases. Non-pooled studies showed health-denoting associations for neurological and cancer-related outcomes as well as respiratory mortality.
Vanaken and Danckaerts26	21 studies including 12 cross-sectional studies, 7 longitudinal studies, and 2 ecological studies	Land use data, NDVI, subjective measures like time spent in greenspaces evaluated using questionnaires, and distance to nearest greenspace	Emotional and behavioral difficulties, mental well-being, and neurocognitive development	There was a beneficial association between greenspace exposure and emotional and behavioral problem. There was limited evidence in support of a beneficial association between greenspace exposure and mental well-being and depressive symptoms. The current evidence suggested that physical activity, air pollution and social interaction mediated these associations.
Browning and Rigolon35	13 studies including 12 observational studies and 1 experimental study	NDVI, tree canopy cover, and green view	Academic performance	Approximately two-thirds of the reviewed studies showed non-significant associations between greenspace and academic performance, and the other studies reported mixed associations.
Shepley et al.29	45 papers, all of which were ecological studies	Parks, community gardens/greening, vegetated streets and walkways, tree and ground cover, and undeveloped or partially developed green areas	Murder, assault and theft.	Presence of parks and other greenspaces reduced urban crime.
Hunter et al.31	38 studies, of which were experiments or quasi-experiments with controlled pre-post designs (n = 21), uncontrolled pre-post design (n = 6) or controlled post-design (n = 8)	Park-based urban greenspace interventions, greenways/trails, urban greening, and greening interventions	Health and wellbeing	There was strong evidence for park-based and greenway/trail interventions on park use and physical activity for greened vacant lots on health and wellbeing (e.g., reduction in stress) and social outcomes (e.g., reduction in crime, increased perception of safety); there was also sufficient evidence for urban street trees increasing biodiversity.
Jo et al.30	37 articles, all of which were experiments	Real life nature stimuli like green plants, flower, and/or wooden materials; exposure to images of natural elements like slides, photos, videos of forests and/or urban park landscapes	Brain activity and autonomic nervous activity	Viewing natural scenery and visual contact with flowers, green plants, and wooden materials had positive effects on cerebral and autonomic nervous activities compared with control groups.
Lakhani et al.34	18 studies	Green care farm, forest therapy, gardens, and outdoor adventure programs	Psychological, emotional and social health domains	Engaging with gardens and gardening favorably impacted the emotional and social health of people with dementia.
Lambert et al.36	18 studies (4 studies on greenspace) including 14 cross-sectional studies, 2 longitudinal studies, and 2 studies with a combination of longitudinal and cross-sectional designs	Neighborhood greenness	Time spent in outdoor play	Neighborhood greenness was a predictor of more time spent in outdoor play (one longitudinal reported reverse association).
Mygind et al.33	26 studies (11 in the meta-analysis) including 3 experimental studies, 16 experimental within-subject randomized crossover trials, 3 quasi-experimental studies within-subject design, and 4 quasi-experimental with controlled before-and-after studies	Seated relaxation or walking in natural environments over the course of 10 min to 8 weeks	Psychophysiological outcomes including serum and salivary cortisol, heart rate variability, salivary amylase, adrenaline, noradrenaline and dopamine as well as cortisol awakening response	Seated relaxation and walking in natural environments enhanced heart rate variability more than the same activities in control conditions. Associations between nature exposure and cortisol were mixed.
Roberts et al.32	33 studies including 16 randomized crossover studies, 5 non-randomized crossover studies, 3 2×2 factorial design studies, 6 randomized parallel group study, 1 parallel group study, and 2 single group crossover studies	Spending 10 to 90 min in natural environments	Depression	A small effect was found for a reduction in depressive moods following exposure to nature environments (effect sizes ranged from -2.30 to 0.84).
de Keijzer et al.39	59 studies including 44 cross-sectional studies, 4 longitudinal studies, and 1 ecological study	Residential exposure to greenspace including NDVI, proportion of greenspace in a certain area, distance to the nearest greenspace, and tree canopy, among others	Mental health, cognitive function, physical capability, morbidity, cardiometabolic risk factors, and perceived wellbeing	There was limited evidence for protective associations between greenspace and morbidity, mental health, cognitive function, physical capability, cardiometabolic risk, and perceived wellbeing.
Hartley et al.48	7 studies including 4 cross-sectional studies and 3 cohort studies	NDVI and land cover, among others	Asthma	No significant association between greenness and children asthma was found.
Hu et al.8	29 studies including 22 cross-sectional studies, 6 cohort studies, and 1 case-control study	NDVI, tree cover, distance to greenspaces, residential surrounding greenspace, visual access to greenspace, and time spent in greenspaces	Birth weight, small gestational age, preterm birth, low birth weight, gestational age, etc.	An increase in residential greenness was generally associated with higher birth weight and lower odds of low birth weight. No associations were found between residential greenness and preterm birth and small gestational age.
Islam et al.49	23 studies including 10 cohort studies, 11 cross-sectional studies, and 2 studies without a study design explained	NDVI, distance to greenspace, and street tree density, among others.	Perinatal health (e.g., birth weight, gestational age, atopic dermatitis), physical activity, respiratory health (e.g., asthmatic symptoms, wheezing) and psychological health (e.g., memory, attentiveness, emotional well-being, etc.)	An increase in greenspace was associated with increased birth weight, decreased risk for low birth weight, increased levels of physical activity, lower risk of obesity, and inattentiveness. Associations between greenspace and respiratory diseases were mixed.
Kim et al.55	27 studies including 14 cross-sectional studies, 5 quasi-experimental studies, 5 randomized controlled trials, and 1 crossover trial, 1 cohort study, and 1 longitudinal study	NDVI, walking in forests, and gardening activities, among others	Physiological benefits, psychological benefits, social health, perceived general health, and physical activity	Greenspace was improved physiological and psychological indicators as health as well as expanded the social networks of older people.
Luo et al.47	57 studies (67 analyses) including 46 cross-sectional studies and 11 cohort studies	Residential proximity to greenspaces, NDVI, proportion of greenspace, and number of parks in a certain area, among others	Weight status (e.g., body mass index or BMI, waist circumference, overweight, obesity, etc.)	More than half of the reviewed studies reported beneficial associations between greenspace and overweight/obesity; meta-analyses showed that NDVI, but not other metrics, was associated with lower odds of overweight/obesity.
Mmako et al.43	19 studies including 12 qualitative studies, 4 quantitative studies, and 3 mixed-methods studies	Attending to plants and animals, nature inspired crafts, exercise and social interaction, and walking outdoors	Engaging in meaningful activities, empowerment, positive risk taking and reinforcing identity	Greenspace may enable an active and meaningful community-life, despite cognitive decline.
Putra et al.42	15 studies including 6 cross-sectional studies, 6 experiments, and 3 longitudinal studies	NDVI, percentage of greenspace, residential proximity to greenspace, land cover map, and Google Street View, among others	Prosocial behavior	Exposure to greenspace may potentially increase prosocial behavior among children and adolescents but the volume and quality of evidence was not yet sufficient to draw conclusions on causality.
Rojas-Rueda et al.37	9 studies all of which were cohort studies	NDVI	All-cause mortality	Increased residential greenness was associated with decreases in all-cause mortality.
Rugel and Brauer40	51 studies (12 on greenspace) including 25 prospective cohort studies, 6 ecological studies, 10 cross-sectional studies, 4 retrospective cohort studies, 2 case-control studies, one case-crossover, 1 individual-level time series study, 1 ecological time-series study, and 1 study integrating both ecological and cross-sectional data	NDVI, gardening, number of greenspaces, and access to greenspace, among others	Diabetes, term birthweight, respiratory diseases, infantile atopic dermatitis, mortality, acute ischemic stroke, CVD, asthma and mortality	There was limited evidence for direct associations between natural environments exposure and chronic respiratory diseases and adverse reproductive outcomes; there was evidence that associations between natural environments and COPD were partially explained by adverse effects of traffic-related air pollution.
Shin et al.41	13 studies including 7 cross-sectional studies, 5 intervention studies, 2 randomized controlled trials, and 1 case report	NDVI, tree canopy, land cover, natural amenity index, neighborhood access to park or forest, and window facing to greenspace from home, among others	Sleep	Higher greenspace exposure was associated with a reduced risk for short sleep and poor sleep quality.
Shuda et al.38	12 studies including 8 cross-sectional studies and 4 RCTs	Walking in a natural setting, nature sounds, and viewing a color/sound tape of natural environment, among others	Perceived stress and physiologic stress	There was an inverse relationship between nature exposure and various physiologic and perceived stress.
Thomsen et al.46	113 studies, of which 74% used quantitative data, 18% used qualitative data, and 8% used a mixed-methods approach	Wildland recreation activities like hiking, camping, and paddling sports	Physical activity, cardiovascular health, muscle strength/bone, mass endurance, obesity, blood pressure, respiratory health, flexibility, sleep quality, self-esteem, emotional well-being, perceived stress/anxiety, family friend functioning, coping with illness/disorder, quality of life, hopelessness/depression, flourishing/happiness/joy, youth behavioral/emotional, and mindfulness	Wildland recreation has the potential to improve physical and mental health, including physical activity, self-esteem, and perceived stress.
van den Bogerd et al.44	37 studies including 18 experimental and intervention studies and 19 cross-sectional or cohort studies	Campus greenspace	Students’ well-being, academic outcomes, and outcomes related to the pathways of mitigation, restoration, and instoration	There was limited evidence for the effects of nature in the study environment on students’ well-being, academic outcomes, or outcomes related to the possible underlying pathways.
Wolf et al.45	201 studies including 56 experimental studies, 26 natural/quasi-experimental studies, 11 longitudinal studies, 69 cross-sectional studies, 24 modelling studies, and 14 time-series studies	Experience or visit to forest or woodland, canopy cover, individual trees, clusters of trees, associated measures like pollen, moss, and tree loss to emerald ash borer; viewing images/tapes of trees, forest/woodland/land cover, experiencing trees in a park, and view of trees/forest through a window	Psychological and cognitive outcomes like mental acuity, stress; physiological measures such as heart rate, cortisol, and glucose levels; self-reported symptoms of illness and allergies; modelling of human health impacts related to heat and air quality; actual air quality, hospitalization and medical records, medication usage, neurological measures, etc.	Greenspace can reduce environmental hazards levels like air pollution, ultraviolet radiation, heat exposure, and pollen; greenspace can also restore capacities like attention restoration, mental health, stress reduction, and clinical outcomes; greenspace can build capacities including birth outcomes, active living, and healthy weight status.
Yuan et al.7	22 studies (8 in the meta-analysis) including 18 cohort studies and 4 cross-sectional studies	NDVI, walkable greenspaces near the residence, urban greenspace visits, and number or size of parks in a certain area, among others	Mortality and cardiovascular outcomes	Most studies showed reductions in the risk of all-cause mortality and total cardiovascular disease with increased in residential greenness.
Zhang et al.9,19	14 studies including 10 cross-sectional studies, 3 controlled experiments, and 1 longitudinal study	NDVI, percentage of greenspace for a certain area, and views to greenspace, among others	Mental well-being	There were beneficial associations between greenspace exposure and reduced stress, positive mood, less depressive symptoms, better emotional well-being, improved mental health and behavior, and decreased psychological distress in adolescents.
Andersen et al.54	20 human studies with pre-post study design	Forest bathing	Pro- or anti-inflammatory cytokines in serum, numbers and percentages of immune cell subsets and expression of cytotoxic mediators, and cytotoxic NK cell activity	There exist positive effects of nature exposure on immunological health parameters, such as anti-inflammatory, anti-allergic, anti-asthmatic effects, or increased natural killers cell activity.
Davis et al.52	45 studies including 36 cross-sectional studies, six longitudinal studies, two pseudo-experimental studies, and one case-control study	NDVI, proportion of nature environment, distance to nearest nature environment, reported amount or quality of greenness, time spent in nature environment	Academic achievement, emotional and behavioral functioning, well-being, social functioning, cognitive skills, prevalence of doctor diagnosed disorders	There was sufficient evidence for NDVI and emotional and behavioral well-being, but the evidence for other comparisons were limited.
Li et al.51	29 studies including 24 longitudinal studies and 5 cross-sectional studies	Lifelong exposure to NDVI, land cover/land use class, access to public greenspace, access to private greenspace, tree cover, urbanicity, self-reported frequency, self-reported duration, quality of public space audit, self-reported quality	Incidence of mental disorders, psychiatric symptoms, emotions, behavioral problems, cognitive function, and subjective well-being	Early-life nature exposure was generally beneficially associated with five domains of mental health including incidence of mental disorders, psychiatric symptoms and emotions, conduct problems in children, cognitive function, and subjective well-being, although inconsistencies were also reported.
Porcherie et al.53	29 studies including 19 cross-sectional studies, 4 cohort studies, 2 case-control studies, two qualitative studies, one quasi experimental studies, and one systematic review and meta-analysis	Playgrounds or recreational areas, and coverage or distance to natural space, NDVI, census unit, and proportion of land cover	Lung cancer, bladder cancer, breast cancer, skin cancer, larynx cancer, non-specific cancer mortality, non-specific carcinogenic risk, and prostate cancer.	Evidence concerning greenspace and cancer risk is limited and mixed.