A systematic review on the relationship between the built environment and children’s quality of life

Background: Evidence of the effects of the built environment on children has mainly focused on disease outcomes; however, quality of life (QoL) has gained increasing attention as an important health and policy endpoint itself. Research on built environment effects on children’s QoL could inform public health programs and urban planning and design. Objective: We aimed to review and synthesize the evidence of the relationship between built environment features and children’s QoL. Methods: Five research databases were searched for quantitative peer-reviewed studies on children between 2–18 years, published in English or German between 2010–2021. Only primary research was considered. Included studies (n=17) were coded and methodologically assessed with the Joanna Briggs Critical Appraisal Checklists, and relevant data were extracted, analyzed, and synthesized, using the following built environment thematic framework: 1) neighborhood natural environment, 2) neighborhood infrastructure, and 3) neighborhood perception. Results: Green space was positively associated with children’s QoL. Infrastructure yielded inconclusive results across all measured aspects. Overall neighborhood satisfaction was positively correlated with higher QoL but results on perceived environmental safety were mixed. Conclusions: Most studies are correlational, making it difficult to infer causality. While the positive findings of green space on QoL are consistent, specific features of the built environment show inconsistent results. Overall perception of the built environment, such as neighborhood satisfaction, also shows more robust results compared to perceptions of specific features of the built environment. Due to the heterogeneity of both built environment and QoL measures, consistent definitions of both concepts will help advance this area of research.


Background
Quality of life (QoL) -a health and wellbeing indicator-has become increasingly important in research on children (1)(2)(3).QoL is a multidimensional concept that involves one's life perception, including physical and mental health, the emotional state, social relationships, environmental features, and cultural values (3)(4)(5)(6).As such, QoL is closely linked to wellbeing, a concept focused on three domains: physical, mental, and social health (7).For the purpose of this paper, we consider QoL and wellbeing as interchangeable.
To move beyond traditional health indicators such as mortality and morbidity, QoL introduces a more humanistic element into health research with a focus on an individual's holistic wellbeing and health (4).QoL measured in children can be used to evaluate interventions, explore facilitatory conditions, inform policies, and support resource allocation based on QoL barriers (8).To date, QoL has been studied in the context of physical activity, social relationships, and mental health and in clinical research on cancer, cardiovascular disease, diabetes, and asthma (3,4,7,9).At the same time, the built environment has also been shown to in uence children's health (10)(11)(12).Built environment is de ned as the physical surroundings and the perception of these, including land use, cleanliness and aesthetics, and infrastructure (10,11,13).However, the role of built environment measures in children's QoL is not well understood.
Previous research has largely focused on single aspects of the built environment, mainly green space, and their effects on children's physical and mental health (12,14).Higher rates of air pollution and noise, greater access to fast-food restaurants, and less availability of and accessibility to green spaces in urban areas have been associated with poorer physical health in cross-sectional studies (10,11).Physical activity has been associated with active commutes such as walking and cycling in pedestrian-friendly neighborhoods, particularly those with greater amounts of green space, proximity to parks, and quality neighborhood features such as street connectivity and self-reported walkability (10,11,13).Perceived safety as it relates to the physical built environment and adequate streetlights have also been related to physical activity (10,11).Similarly, green space accessibility and use have been shown to improve mental health by reducing stress, promoting resilience, and improving mood (15,16).
To date, no systematic review has examined the built environment in relation to children's QoL.As such, we aimed to review the evidence by identifying, evaluating, and synthesizing relevant studies; determining factors that facilitate or impede QoL in children; and exploring how these factors can be considered in programs and urban design.

Methods
This systematic review was conducted in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (17) and registered in the International Prospective Register of Systematic Reviews (PROSPERO; CRD42021286640).

Population
Our target population included children aged 2-18 years.Because common QoL questionnaires require the child's developmental stage to be advanced enough to observe and describe various life dimensions, children < 2 years have been excluded (18).

Exposure
The exposure variable consisted of neighborhood built environment measures, de ned as the structural aspects of the physical living environment.Since previous literature has indicated the in uence of subjectively perceived neighborhood environment on health outcomes, we also included neighborhood perception, and satisfaction (19).Furthermore, since environmental perceptions are speci c to the built environment, we expanded the neighborhood perception by concepts of safety as it relates to the environment and tra c.As such, we excluded safety perception of crime as it pertains to the social environment and is thus outside the scope of this paper.The exposure variable was divided into three categories: 1. Neighborhood natural environment: Proximity or quantity of green and blue space, parks, etc., in the context of an urban landscape.
2. Neighborhood infrastructure: Measures of tra c, street connectivity, and availability and accessibility of public transportation, and self-reported outdoor places for play.3. Neighborhood perception: Subjective neighborhood perception, including overall neighborhood satisfaction, perceived walkability, and environmental safety.

Outcome
The outcome consisted of standardized and validated measures of children's QoL (self-or parent-reported).Due to QoL being closely linked to wellbeing, this systematic review focuses on both concepts, even though only QoL will be used as a term henceforth.

Other Inclusion Criteria
Only peer-reviewed quantitative primary research was included.All studies were limited to English and German due to the development of the two largest QoL questionnaires: the KINDL questionnaire (originally developed in German) and the Pediatric Quality of Life Inventory (PedsQL, originally developed in English).
To ensure the most recent research, we included studies from January 2010 to December 2022.

Exclusion Criteria
Studies on clinical populations and qualitative studies were excluded.To ensure a focus on the neighborhood built environment, we also excluded studies focused on the school or home environment, and studies that assessed safety in terms of interpersonal relations with neighbors or community members (e.g., community trust, social cohesion, or neighbor disputes).Other exclusion criteria included unavailable full-texts, non-human subjects, study protocols, and development, validation or feasibility studies.

Search Strategy & Data Collection
We applied a 4-step search strategy with the main search occurring between August and September 2021, and two updated searches in January and December 2022.First, we identi ed keywords through a preliminary search in PubMed.Second, we developed a full search string tailored to the following databases: PubMed, Cochrane Reviews, CINAHL, PsycINFO, Embase, and Web of Science (see Appendix A for tailored search strings).Third, the databases were searched.Fourth, reference lists of all eligible studies for full-text review were screened for additional qualifying studies.

Study Selection
All search results (n = 6,571) were exported to EndNote and ltered for duplicates.The remaining studies were exported into Excel and LH manually ltered for remaining duplicates.LH screened titles and abstracts of the remaining studies for inclusion (see Appendix B for exclusion details).The remaining 49 studies were divided among three reviewers (LH, MS, HK) for full-text screening.Two reviewers screened each study.In case of a dispute, the third reviewer was consulted, and the case was discussed until a consensus was reached.Thirty-two studies were excluded after full-text screening (see Appendix C for details).

Data Extraction & Synthesis
The nal 17 included studies were divided among the three reviewers and coded based on: research question, exposure/intervention, outcome, study design and setting, population, methods, results, discussion, and limitations.Additionally, methodological quality was assessed with the Joanna Briggs Institute Critical Appraisal Checklist in accordance with study types (20).The following cut-offs were used: Poor: >3 items marked with "no" or "undetermined" Fair: 2-3 items marked with "no" or "undetermined" Good: < 2 items are marked with "no" or "undetermined" Due to the heterogeneity of built environment aspects and the small sample size of included studies, it was not feasible to conduct a meta-analysis.Each study was then categorized according to a thematic framework developed by the authors based on previous literature: 1) neighborhood natural environment, 2) neighborhood infrastructure, and 3) neighborhood perception.Subsequently, the relationship between built environment and children's QoL was analyzed, evaluated, and interpreted in the context of other studies within the same category.Some studies intersected categories due to measuring multiple exposures.
In addition, this review included studies that utilized both self-reported and objectively measured built environment.

Results
Figure 1 shows this study's PRISMA owchart.More detailed exclusion criteria can be found in Supplemental Material S1 and S2.

Independent variable: Built environment
Studies encompassed a range of objective and subjective built environment measures.Four studies assessed the built environment through objectively measured means only, including landscape spatial patterns and green space quantity utilizing the Geographic Information System (GIS), the Scottish Neighborhood Deprivation Index, street connectivity, facility and playground density, and tra c (21,24,25,32).Eleven studies utilized subjective survey measurements of the built environment including questions regarding neighborhood perception and satisfaction, housing, tra c, environmental safety, public transportation, accessibility and quality of green spaces, playgrounds, open spaces, and spaces for play (23, 26-31, 33, 34, 36, 37).One study combined objectively and subjectively measures of the built environment (22), and another single study utilized an intervention design exposing the participants to green space in the form of small urban parks, larger urban parks, and forest settings (35).

Dependent variable: Children's QoL
QoL measurements varied signi cantly.The Pediatric Quality of Life Inventory (PedsQL) ( 5), KINDL (6), and KIDSCREEN (38), were the most commonly used scales in seven of the 17 studies.Other measures unique to each study can be found in Table 1.

Review ndings
Figure 2 shows the distribution of studies by the three thematic categories.
Neighborhood Natural environment and QoL studies focused on the natural environment with objective measures including number of tree areas, green space quantity, and percentage of green and blue spaces (i.e., bodies of water) in neighborhoods and subjective measures including presence of green, blue or open spaces, and accessibility to these spaces.
On one side, most studies showed a positive relationship between the natural environment and children's QoL (22, 25, 27-30, 32, 34, 35).More and greater sizes of tree areas or higher proportions of green space within the neighborhood landscape were associated with higher QoL (22,25,30,32).These ndings were corroborated by studies utilizing self-reported measures (27)(28)(29).On another side, two studies found negative associations between greater distances from one tree area to another and self-reported access to green space and QoL (22,32).Two other studies did not nd signi cant results for the proportion of green space and children's QoL (21,24).
The evidence is mixed regarding blue space.While one study found a negative association of blue space percentage in the neighborhood with children's QoL (25), another reported a positive relationship (29).
The only intervention study in this systematic review utilized a school lunch break to expose children to either a forest setting or a large or small urban park (35).The authors found a positive relationship between exposure to different kinds (and sizes) of green space and children's wellbeing (35).The authors also found a dose-response relationship with small urban parks yielding the smallest effects on wellbeing (still signi cant) compared to indoor lunch breaks and large forest settings yielding the greatest increase in self-reported wellbeing (35).

Neighborhood Infrastructure QoL
Seven studies included such as street connectivity, walkability, athletic and recreational facility density, and neighborhood deprivation-a measure of neighborhood resource availability and access to employment, education, health, and housing (21,26,28,(32)(33)(34)36). The evidence is mixed and inconclusive.Two studies found non-signi cant results (21,24).Public transportation access and use by children without adult supervision was negatively associated with children's QoL (33).Self-reported places to play outside the home also showed mixed ndings with one study showing a positive relationship with children's QoL, and two other studies not con rming these ndings due to statistical insigni cance (26, 27, 36).

Discussion
This is the rst systematic review on the relationship between the built environment and children's QoL.Previous research, mostly in adults, has been limited largely to the role of green space in disease outcomes.However, as QoL gains recognition as an important health outcome in its own right, understanding how diverse factors in the neighborhood built environment affect children's QoL is important to policy and program development and urban design.
Our ndings yielded robust evidence for the natural environment and mixed or inconclusive evidence for infrastructure and neighborhood perception.Green space showed a positive relationship with children's QoL, further supported by a dose-response relationship found in one intervention study.The more green space available in a neighborhood, the higher the QoL among children.This is in line with previous research focused on the bene ts of green space in urban environments on mental health, physical activity, and wellbeing across different adult populations (39)(40)(41).However, two studies found no signi cant relationship, indicating measurement errors, small sample sizes, or a homogenous context not providing enough variability in exposure and outcome measures.
While green space is positively associated with children's QoL in some studies, the importance of open spaces should be highlighted.In Houston (Texas), Hispanic children's QoL was positively in uenced by a greater number of urban forests and by longer distances between these tree patches (22).This highlights the importance of open spaces, including settings with clear edge conditions without dense understories, to provide a sense of safety due to a greater ability to see far, which in turn in uences QoL (22).This is in line with a Norwegian study showing a negative relationship between self-reported access to green spaces and children's QoL in densely populated areas (32).Hence, while urban areas provide more access to parks, these spaces are also associated with tra c, safety concerns, and crowding (32).Thus, the quality of parks and green spaces may have a greater in uence on QoL than quantity or accessibility.
Although green spaces are an essential aspect of the built environment, other aspects such as blue spaces are understudied.These have been proposed to be an effect modi er on the relationship between nature and QoL (42).Blue space can contribute to physical activity through access to water sports, and to social health through social gatherings (42).In our review, blue space showed mixed evidence.While blue space was positively associated with children's QoL in one study, another found the opposite; however, neither study assessed the quality of blue spaces.It is conceivable that cleaner and aesthetically pleasing blue spaces contribute to improved wellbeing, whereas polluted urban rivers or canals may have the opposite effect (25).Furthermore, green and blue spaces are often intertwined with blue spaces being situated within parks, making it di cult to extract the sole effect of blue space on QoL (42).
Our ndings showed inconclusive results for neighborhood infrastructure, measured mainly via surveys on select dimensions.Most studies focused on neighborhood deprivation, public transportation accessibility, facility density, street connectivity, and walkability; none of these demonstrated a signi cant relationship with children's QoL (21,24,32,33).However, these constructs were researched in isolation and not as a holistic concept, neglecting potentially synergistic effects.Furthermore, self-reported places to play showed inconclusive results with a German study on 6-years olds showing a positive relationship with QoL and two Canadian studies not showing signi cant results in children 9 years and older (26, 27, 36).Places to play can more directly affect younger children, while other infrastructure constructs measured in other studies may be more relevant to middle childhood, adolescence, and adulthood.
Overall neighborhood satisfaction showed a more positive association with children QoL than narrow constructs such as environmental safety perceptions.This is in line with previous research highlighting that residents in deprived neighborhoods reported lower neighborhood satisfaction even if green spaces and local amenities were evenly distributed compared to less deprived areas (43).This highlights the importance of subjective or experiential measures of neighborhoods even though research has tended to favor objective, GIS-related measures.Furthermore, the disconnect between perception and objective environment may indicate that other factors beyond the built environment in uence neighborhood satisfaction and health, such as the social environment and the degree to which a neighborhood is collectivist, which have not been well studied in conjunction with the physical built environment (37).
Notably, cause-and-effect relationships are di cult to determine because of the lack of longitudinal studies.Furthermore, we caution against extrapolating ndings from this systematic review across settings.Most studies were conducted in developed countries.Further research is needed to determine how built environment and QoL are related across cultures and countries.
Several challenges have emerged with this review.First, QoL de nitions were heterogeneous, with a blurry distinction between related concepts including happiness, life satisfaction, and self-reported physical and mental health, resulting in a wide range of instruments.A more coherent de nition of QoL is needed to enhance the comparability of studies.Second, there is also a lack of a coherent de nition for built environment measures.Most studies either utilized GIS regarding landscape spatial patterns or study-speci c single questions incorporated into a survey.These neglect the multiple dimensions of the built environment and could explain the non-signi cant ndings.The framework applied in this review can serve as a starting point for a more integrated measurement approach.
Finally, we found contradictory results and inconclusive ndings within all three categories of our thematic framework; a possible explanation is the difference between accessibility versus actual use of these settings.Actual use of green spaces may have a greater effect on children's QoL than access alone (24,44,45).Green space quality may partially explain this difference.Community-tailored social and physical activity programs, ideally supervised, may be ways to increase park use (46-48).Yet, there is a dearth of intervention studies on the built environment in relation to children's QoL and more such studies are urgently needed.

Conclusions
The built environment, especially green and open spaces, and overall neighborhood satisfaction, may play an important role in the QoL or wellbeing of children.Public health programs should integrate with urban design strategies to leverage built environment enhancements to improve children's health.Additionally, social functions of the built environment, the actual use of these spaces, and subjective experience may play a role in the relationship between the built environment and children's QoL, suggesting a need for increased attention to social programs within green spaces and ways of improving neighborhood satisfaction.More prospective and intervention studies are warranted to establish causal pathways between the built environment and children's QoL.

Figure 1 PRISMA
Figure 1 PRISMA Flow Chart

Table 1
Summary and characteristics of included studies Methodological quality was assessed with the Joanna Briggs Institute Critical Appraisal Checklists.The proper checklist was chosen according to study type. *