Urban Green Spaces’ Influence on Civilization Diseases—Meta-Analysis and Critical Review

: This study investigates the influence of urban green spaces on the prevalence of over-weight/obesity, diabetes, and hypertension. The search was run in the PUBMED database, using the search algorithm including combinations of keywords associated with the two concepts: civilization health problems and urban green spaces. A meta-analysis (for 48 studies) and critical review (for 26 studies) were performed. The meta-analysis results show that the presence, accessibility, and quality of green spaces are associated with the decreased prevalence of overweight/obesity (OR 0.86 (95% CI 0.77–0.95), p < 0.001, I 2 99.7%), diabetes (OR 0.83 (95% CI 0.79–0.87), p < 0.001, I 2 67.5%), and hypertension (OR 0.77 (95% CI 0.63–0.92), p < 0.001, I 2 84.9%). In the children population, the influence of green spaces on overweight is unequivocal (OR 0.88 (95% CI 0.72–1.03), p < 0.001, I 2 99.6%) and there is no influence on diabetes control. A green space’s direct influence on systolic or diastolic blood pressure is unequivocal. A green space is associated with a decreased prevalence of civilization diseases. Its positive influence, however, is not so strong in children. The short-term influence of green spaces on blood pressure (e.g., taken as a proxy for mental stress) is unequivocal.


Introduction
Chronic diseases, commonly known as non-communicable diseases (NCDs), are one of the biggest challenges currently facing humanity worldwide.They are the result of not only genetic and physiological but also environmental and behavioral factors.Among the major diseases related to lifestyle are diabetes, hypertension, and obesity.These diseases severely affect quality of life and well-being.Furthermore, healthcare costs associated with the treatment of NCDs impose a considerable economic burden on health services.Changes in lifestyle could prevent many of these chronic diseases, improve health, and reduce the need for expensive treatments.To lessen the impact of NCDs on individuals and society, a comprehensive approach is needed.
Sustainable development of an urban environment may reduce risks to human wellbeing.Many researchers indicate a positive correlation between access to green spaces in urban areas and public health.Exposure to green spaces may reduce the risk of several health problems for many reasons, including the ability to perform physical activity (e.g., [1][2][3]).Although studies on the impact of urban green spaces on the health of people suffering from civilization diseases are numerous, most of them were performed on a local scale (within one city or country).There is a lack of research that tackles this subject on a global scale.It is difficult to assess the impact of green spaces on health because existing research results are often difficult to compare.The main reason can be attributed to the use of different green space measures [2].Some researchers focus on quantity of green space (e.g., green space area as a proportion of the total area within a community, number of green spaces per 10,000 residents [4], the total number of green spaces within 1600 m network buffer from residents' homes [5], parkland density, parkland per 1000 residents [6], amount of green vegetation around the residential address [7]), while others focus on green space quality (e.g., the number, type, and quality of park features and amenities, and overall incivilities [8], access amenities, park facilities, aesthetics features, park quality concerns [9]) and the use of green space (e.g., time spent on walking and moderate and vigorous physical activity in the last seven days [10]).
Also, the definition of green space within an urban area varies considerably in the existing studies.As well, the range of different types of urban green spaces included in a study can vary.Some researchers took into account only natural elements that exist in urban areas, such as street trees, neighborhood parks, and open spaces [11]; others took into account very vast land-use categories, such as gardens, zoos, parks, cemeteries, suburban natural areas, sports fields, golf courses, amusement parks, and allotment gardens [12]; or such as community parks, farms, gardens, nurseries, linear parks, parkways, metropolitan parks, neighborhood parks, regional parks, squares, etc. [13]; or all types of formal, informal, natural, and young people's sports green spaces [1].Some researchers included in their analysis only areas with a limited size, for example: parks larger than 1 hectare, with at least 65% of the land covered with trees [14]; parks of at least 2 hectares in size [1], or 1 hectare [10] or 1 acre [15]; while others defined as a green space any park or garden that was freely accessible to the public, ranging between a regional park (over 400 hectares) and a pocket park (smaller than 0.4 hectares) [16].The smallest green space unit that was included in the study was 19 square meters in size [17].
A frequent measure used to assess a green space's accessibility is the distance to the closest green space from home.The recommended distance to a green space is usually based on the concept of having a green space within a 15-min walk from home [18].Distance buffers used to assess a green space's impact on health within an urban neighborhood vary considerably in different studies.According to some research, buffers reflecting a range of reasonable walking distances are half a mile, one mile [9], and two miles' distance from home [19].Half a mile's distance can be comparable with 800 m of street network buffer (roughly a half-mile distance) and 1 km [17,[20][21][22], which, according to some studies, represents an area that can be accessed in approximately 10-15 min of walking time.In other studies, a 500-m buffer [23] or 400-m buffer [21,24] (roughly a quarter-mile distance) were analyzed.According to several studies, a distance below or equal to a 300-m radius [25], or even a 250-m street network buffer [26], are used.
So far, there is a lack of systematic overview concerning the types of greenery available for urban dwellers and their association with civilization diseases.This study investigates the influence of urban green spaces on the prevalence of three civilization diseases: overweight/obesity, diabetes, and hypertension.Its aim is to summarize the state of this knowledge globally, as well as to identify topics that require further research.

Materials and Methods
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed in this meta-analysis and systematic review [27].

Data Source and Study Strategy
The search was run in the PUBMED database from the inception to 1 February 2024.The search algorithm included all possible combinations of keywords associated with the two concepts: civilization health problems and urban green spaces.
A combination of the following Medical Subject Heading (MeSH) terms indexed within the database comprised the search strategy: 'obesity' or 'overweight*' or 'body mass index' or 'body weight' or 'obese' or 'body mass gain*' or 'body mass loss*' or 'hypertension' or 'hypertensive' or 'blood pressure' or 'diabetes' or 'diabetic' or 'prediabetes' or 'prediabetic' or 'high blood sugar' or 'insulin resistance' or 'metabolic syndrome' or 'diabetes risk' or 'blood sugar control' or 'impaired glucose tolerance' and 'community garden*' or 'urban green space' or 'park' or 'public garden' or 'recreational space' or 'local green space' or 'residential green space' or 'inner city green space' or 'green land cover'.Also, the reference list search was conducted based on the full-text articles meeting the study selection criteria that were identified from the keyword search.
Experimental studies (randomized or controlled trials) published in English were ultimately included in the review, as presented in Figure 1.The publications presenting results from the same intervention or from the same sample were reported together.
Also, the reference list search was conducted based on the full-text articles meet the study selection criteria that were identified from the keyword search.
Experimental studies (randomized or controlled trials) published in English were timately included in the review, as presented in Figure 1.The publications presenting sults from the same intervention or from the same sample were reported together.
All records were also reviewed by an MD, PhD, specialist in internal medicine a cardiology (A.I. K.) with experience in clinical trials to further consider their relevance inclusion.
The required data were extracted and recorded, including the authors' names, p lication year, location, sample size, and study outcome (with 95% CI, SE, and p-value, spectively).

Statistical Analysis
The JASP 0.18.3.0 software package was used for the analysis.The results are sho as forest plots with 95% confidence intervals.
To quantify the degree of heterogeneity between studies, the I 2 statistic was cal lated.The analysis used a random-effects model, which is thought to be a more conser tive approach suitable for cases of high heterogeneity.A p-value ≤ 0.05 was conside significant.All records were also reviewed by an MD, PhD, specialist in internal medicine and cardiology (A.I. K.) with experience in clinical trials to further consider their relevance for inclusion.

Defining Green Space
The required data were extracted and recorded, including the authors' names, publication year, location, sample size, and study outcome (with 95% CI, SE, and p-value, respectively).

Statistical Analysis
The JASP 0.18.3.0 software package was used for the analysis.The results are shown as forest plots with 95% confidence intervals.
To quantify the degree of heterogeneity between studies, the I 2 statistic was calculated.The analysis used a random-effects model, which is thought to be a more conservative approach suitable for cases of high heterogeneity.A p-value ≤ 0.05 was considered significant.

Defining Green Space
Apart from reporting the presence/absence of a green space, in some studies, quantitative methods to assess greenery are used.
NDVI is a proxy for overall vegetation level, taking values from −1 to +1, where the positive values indicate higher greenness.EVI is similar to NDVI with a corrected atmospheric and soil background.
A green space's accessibility is described using: the distance to a green space, measured in a straight line or along a street network, or as the presence of a green space in a buffer zone constructed around one's home with various radii, ranging from 100 m to 3200 m (2 miles).
In studies where the participants self-reported having an accessible park in their neighborhood, the walking distance to the green space was defined as taking less than 15 min to walk to [22,35].

Overweight/Obesity
The most common way to diagnose overweight and obesity is to calculate a Body Mass Index (BMI), which is calculated by dividing the height by the weight of an individual.These parameters are self-reported by the participants of a study or taken by a medical professional.For children, a BMI z-score is used (BMI adjusted for age and sex) and BMIp95 (actual BMI divided by 95th percentile of BMI for specific age and sex).
Overweight is defined in adults as BMI > 25 kg/m 2 and obesity as BMI > 30 kg/m 2 , while in children, these are defined as BMI > 85 percentile and > 95 percentile, respectively.
In some studies, the waist-to-hip circumference ratio (WHR) [11], percentage of body fat, or skinfold thickness [36] are used as overweight/obesity proxy.

Characteristics of the Included Studies
Thirty studies provided quantitative data adequate to be included in the meta-analysis-17 of them investigated the adult population, while 13 considered children.The fifteen studies remaining (6 in the adult population, 9 in the children population) are included in the review (Table 1).

Key Findings
A green space's presence, accessibility, and quality are linked to the prevalence of overweight/obesity.The meta-analysis results show that green spaces are associated with a decreased prevalence of overweight/obesity-OR 0.86 (95% CI 0.77-0.95);p < 0.001; I 2 99.7% (Figure 3).
The number of studies also allows the performance of separate analyses for the adult and children population, and the results are similar in the adults-OR 0.85 (95% CI 0.75-0.96);p < 0.001; I 2 99.4% (Figure 3) but not in the children population-OR 0.88 (95% CI 0.72-1.03);p < 0.001; I 2 99.6% (Figure 4).Interestingly, in 1 study of the adult population [1] and 2 studies of the children population [47,52], the proximity of green space is associated with a higher probability of overweight/obesity.Interestingly, in 1 study of the adult population [1] and 2 studies of the children population [47,52], the proximity of green space is associated with a higher probability of overweight/obesity.

Key Findings
A green space's presence, accessibility, and quality are linked to the prevalence of overweight/obesity.The meta-analysis results show that green spaces are associated with a decreased prevalence of overweight/obesity-OR 0.86 (95% CI 0.77-0.95);p < 0.001; I 2 99.7% (Figure 2).Interestingly, in 1 study of the adult population [1] and 2 studies of the children population [47,52], the proximity of green space is associated with a higher probability of overweight/obesity.In the children population, however, BMI negatively correlates with green space only in 3 studies [23,24,56], while in 5 studies, no difference is observed.
In the study concerning maintaining healthy body mass [20], having a green recreational space near the home increases the probability of success.

Diabetes
For the purpose of the review, type 2 diabetes (this type being a civilization disease) is taken into consideration.
In the chosen studies, an individual with diabetes self-reports a diagnosis, and medication or data are retrieved from medical reports.It is newly diagnosed when glucose concentration in a blood sample exceeds 7 mmol/L after overnight fasting.
To assess the severity of metabolic problems in diabetes, a percentage of glycated hemoglobin (HbA1c) is used [21].
As a proxy for prediabetes, a homeostatic model assessment of insulin resistance (HOMA-IR) is used [7,57].

Characteristics of the Included Studies
Thirteen studies provide quantitative data adequate to be included in the metaanalysis.The four studies remaining are included in the review (Table 2).

Key Findings
A green space's presence, accessibility, and quality are linked to the prevalence of diabetes.The meta-analysis results show that green space is associated with decreased prevalence of diabetes-OR 0.83 (95% CI 0.79-0.87);p < 0.001; I 2 67.5% (Figure 5).

Key Findings
A green space's presence, accessibility, and quality are linked to the prevalence of diabetes.The meta-analysis results show that green space is associated with decreased prevalence of diabetes-OR 0.83 (95% CI 0.79-0.87);p < 0.001; I 2 67.5% (Figure 5).
There is an observed negative correlation between green space and HOMA results in children, suggesting a lower risk of diabetes development [7,57] but no difference in the percent of HbA1c, suggesting the lack of green space's influence on diabetes control [21].

Hypertension
In the chosen studies, an individual with hypertension self-reports a diagnosis, and medication or data are retrieved from medical reports, and is newly diagnosed when the blood pressure (BP) measured by a medical professional exceeds 140/90 mmHg or 95th There is an observed negative correlation between green space and HOMA results in children, suggesting a lower risk of diabetes development [7,57] but no difference in the percent of HbA1c, suggesting the lack of green space's influence on diabetes control [21].

Hypertension
In the chosen studies, an individual with hypertension self-reports a diagnosis, and medication or data are retrieved from medical reports, and is newly diagnosed when the blood pressure (BP) measured by a medical professional exceeds 140/90 mmHg or 95th percentile adjusted for sex, age, and height in children.Systolic blood pressure (SBP) and diastolic blood pressure (DBP) are reported.

Characteristics of the Included Studies
Five studies provide quantitative data adequate to be included in the meta-analysis.The seven remaining studies are included in the review (Table 3).Four studies [65][66][67][68] are experimental studies investigating a green space's short-term influence on blood pressure.

Key Findings
A green space's presence, accessibility, and quality are linked to the prevalence of hypertension.The meta-analysis results show that green space is associated with a decreased prevalence of hypertension-OR 0.77 (95% CI 0.63-0.92);p < 0.001; I 2 84.9% (Figure 6).As for adults, a green space does not directly influence the systolic nor the diastolic measured BP [13].In children, however, the results are unequivocal-in one study, there lower SBP associated with green space is reported [69], while the other reported no difference [21].
As for the studies investigating a short-term green space influence on blood pressure, 2 studies report a reduction of DBP [65] or both systolic and diastolic BP [67], and 2 studies do not report differences [66,68].

Discussion
The presented review includes highly heterogeneous studies, which allows a wide perspective of the problem to be assessed.However, it should be noted that there is an over-representation of studies from Europe and North America, especially those concerning obesity.This may present some limitations in translating the results to the global population.It is worth noting that 80% of the studies based on green space accessibility directly assessed by the authors are less prone to error than the self-declaration of study participants.Unfortunately, the overweight/obesity prevalence is largely based on selfreported weight and height (53% of the studies), which may not be fully reliable.
It seems that the possibility of =contact with nature, even limited to an urban green space only, is associated with the reduced prevalence of NCDs.However, an urban environment is a very complex system.Some authors claim that modern, more expensive districts usually offer more green spaces of better quality.Yet, they attract tenants with higher incomes, which allows them to follow a well-balanced diet and gives them better healthcare possibilities.On the other hand, there are also districts devoid of green spaces but with high-income tenants who adhere to a healthy lifestyle.As for adults, a green space does not directly influence the systolic nor the diastolic measured BP [13].In children, however, the results are unequivocal-in one study, there lower SBP associated with green space is reported [69], while the other reported no difference [21].
As for the studies investigating a short-term green space influence on blood pressure, 2 studies report a reduction of DBP [65] or both systolic and diastolic BP [67], and 2 studies do not report differences [66,68].

Discussion
The presented review includes highly heterogeneous studies, which allows a wide perspective of the problem to be assessed.However, it should be noted that there is an over-representation of studies from Europe and North America, especially those concerning obesity.This may present some limitations in translating the results to the global population.It is worth noting that 80% of the studies based on green space accessibility directly assessed by the authors are less prone to error than the self-declaration of study participants.Unfortunately, the overweight/obesity prevalence is largely based on self-reported weight and height (53% of the studies), which may not be fully reliable.
It seems that the possibility of =contact with nature, even limited to an urban green space only, is associated with the reduced prevalence of NCDs.However, an urban environment is a very complex system.Some authors claim that modern, more expensive districts usually offer more green spaces of better quality.Yet, they attract tenants with higher incomes, which allows them to follow a well-balanced diet and gives them better healthcare possibilities.On the other hand, there are also districts devoid of green spaces but with high-income tenants who adhere to a healthy lifestyle.
There is also a problem with the interpretation of self-reported access to green space that is of low quality or is in a dangerous neighborhood.Probably, its protective effect will be considerably reduced.
In some studies, the effect of income level on NCDs is more prominent than that of green space.It poses the question of whether it is green space that has a mitigating effect on civilization diseases, or if it is rather a proxy for social status.
A recommended concept of urban planning is having green space within a 15-min walk from home.However, in some studies [1,47,52], the proximity of green space does not prevent obesity.Apart from the quality of green space, this phenomenon may be explained by an assessment of motivation.A good quality, well-equipped park not within walking distance may be frequented by better-motivated users, who, if they already have made the time to get there, stay there for longer and commit more to their exercises.
Interesting is the question of the lack of protective effect of green spaces on overweight prevalence in the children population.Apart from the quality and safety of green spaces and a possible motivation factor, this observation may be explained by the fact that, nowadays, children may need more structured recreational green spaces, as well as the encouragement of parents, to perform physical activities outdoors.
This review helps to outline the problem of urban green spaces and their influence on NCDs.Further, more uniformly and well-designed studies are necessary to determine the qualitative and quantitative need for greenery in a sustainable urban environment, taking into account area per capita, plant composition, and distance from residence.

Conclusions
Green spaces are associated with a decreased prevalence of overweight/obesity.Its positive influence, however, is not so strong on children's BMI, and some studies even report negative influence.
Green space is associated with a decreased prevalence of type 2 diabetes.A green space may prevent the development of type 2 diabetes in children.However, green space does not improve diabetes control.
Green space is associated with a decreased prevalence of hypertension, but no relationship is observed between green space and blood pressure as a continuous variable.The short-term influence of green space on blood pressure (e.g., taken as a proxy for mental stress) is unequivocal.

Table 1 .
Summary of the characteristics of the 45 included studies.
1Values in bold are statistically significant.

Table 2 .
Summary of the characteristics of the 17 included studies.

Table 3 .
Summary of the characteristics of the 12 included studies.