摘要：Objectives. We investigated the association between physical and social neighborhood environments and fifth-grade students’ physical activity and obesity. Methods. We collected data on 650 children and their primary caregivers during phase 1 of Healthy Passages, a multisite, community-based, cross-sectional study of health risk behaviors and health outcomes in children. We conducted independent systematic neighborhood observations to measure neighborhood physical characteristics, and we analyzed survey data on social processes. We modeled children's physical activity and obesity status with structural equation models that included latent variables for the physical and social environments. Results. After we controlled for children's sociodemographic factors, we found that a favorable social environment was positively associated with several measures of physical activity and that physical activity was negatively associated with obesity in these children. Physical environment was not significantly associated with physical activity. Conclusions. Our findings suggest that neighborhood social factors as well as the physical environment should be considered in the development of health policy and interventions to reduce childhood obesity. The prevalence of childhood obesity in the United States has gone up dramatically in recent decades: overweight prevalence has increased from 6.5% in 1976 to 1980 to 18.8% in 2003 to 2004 among children aged 6 to 11 years. 1 Childhood obesity is worrisome not only because it can cause immediate morbidity, but also because the physical inactivity and poor dietary habits associated with obesity in childhood can persist into adulthood. 2 Several factors at both the individual and contextual levels might contribute to childhood obesity. At the individual level, considerable differences exist in childhood obesity and physical activity levels by socioeconomic status, race/ethnicity, and gender. 3 – 5 For example, Mexican American boys and Black girls are more likely than are other children to be overweight. 6 Adolescent activity levels and correlates of physical activity also vary by gender 7 , 8 and race/ethnicity. 9 At the contextual level, the effects of parenting, the home environment, and developmental and psychological factors on diet, obesity, and physical activity have received significant attention. 10 – 14 Recently, the importance of the broader social and physical environment on obesity has been recognized. 15 – 17 Researchers have investigated the direct and indirect effects of neighborhood environments on physical activity among adults, 18 , 19 but few studies have focused on youths. 17 , 20 In addition, most of this research has focused on the influence of neighborhood physical environment on physical activity. The influence of neighborhood social environment has received less attention. Research has linked only a few aspects of the social environment, specifically neighborhood safety and cohesion, to physical activity and obesity. For our theoretical framework, we drew on the Social Determinants of Health and Environmental Health Promotion model, 21 , 22 which describes how fundamental, intermediate, and proximate socioeconomic processes interacting with the built environment determine population health. We focused on specific relationships between intermediate factors (the physical environment), proximate factors (the social environment as perceived by residents and physical activity), and health (obesity). The social environment, which includes social integration and stressors such as safety, was included as a proximate factor even though it is a community-level factor because it is measured as perceived at the personal level. We were unable to include fundamental factors, such as economic inequalities and residential segregation. Figure 1 depicts the relationships we studied. Open in a separate window FIGURE 1 Theoretical model for childhood obesity. Note. BMI = body mass index. Arrows indicate direction of influence. aData obtained from Systemic Social Observations. bData obtained from questionnaire. cData obtained from measurements. A large amount of literature on the physical environment, physical activity, and obesity addresses several aspects of the neighborhood physical environment. Studies that used ecological models 23 showed that several aspects of the physical environment had an effect on obesity in adults. 24 For example, residents of a mixed-land-use neighborhood (i.e., both residential and commercial) or a high-density neighborhood were likely to be more active because of opportunities to walk to stores and other destinations. However, the empirical evidence on land use and density and adult obesity is mixed. 25 – 31 Little is known about the influence of land use and density on children's physical activity. One of the few studies on this subject did not find a positive relationship between residential density and children's physical activity. 32 One study found that children living in areas with high population density were more likely to walk or bike to school. 33 Traffic and physical disorder (graffiti and litter) in the physical environment are likely to discourage physical activity by increasing perceived danger on the street and public places and reducing a sense of neighborhood social cohesion that might attract outdoor or group activity. Among children, research showed that less traffic and the presence of sidewalks in good condition were associated with more walking or biking to school and other destinations. 8 , 34 , 35 Although physical disorder has been associated with less physical activity and more obesity among adults, 36 one study found no such association in children. 37 The neighborhood social environment may be at least as important to physical activity as the physical environment, but its role has not been adequately studied. Previous research on neighborhood social environments focused primarily on safety. Inadequate neighborhood safety is likely to curb outdoor activities and has repeatedly been correlated with low physical activity levels among schoolchildren. 37 – 40 In qualitative research on barriers to physical activity, middle-school students reported safety concerns as a major barrier. 41 , 42 However, Sallis et al. found no links between parents’ perceptions of neighborhood safety and physical activity in fourth- and fifth-grade students, 43 and another study found a negative association between girls’ physical activity and parents’ perceptions of park safety. 44 Social cohesion has been shown to influence health at the neighborhood level. 45 Neighborhood social cohesion might also influence young people's physical activity levels through several potential pathways. Increased social contact and social exchange among members of a community may lead to the adoption of more-healthful behaviors and a culture favoring fitness. The availability of a network of parents who know each other and who are willing to watch out for neighborhood children (collective socialization of children) could facilitate enforcement of healthful norms, including support for physical activity, as well as increase awareness of programs for youths. Neighborhood collective efficacy, a measure of willingness of neighbors to come together for the common good, facilitates collective action, including improving availability and access to recreational resources for children. 46 Some studies have found that neighborhood cohesion influences physical activity. Social capital at the county level was positively associated with physical activity levels, 47 and neighborhood social cohesion was associated with increased levels of physical activity among older adults. 48 Collective efficacy was associated with lower body mass index (BMI; weight in kilograms divided by height in meters squared) among adults and adolescents. 49 Molnar et al. found that lower social disorder was associated with more recreational activity among children and adolescents. 37 We investigated the association between physical and social neighborhood environment and fifth-grade students’ physical activity and obesity through multiple measures of neighborhood physical characteristics and social processes. We measured neighborhood physical factors with independent systematic neighborhood observations and social processes with survey data. We hypothesized that, after we controlled for children's sociodemographic characteristics ( Figure 1 ), the physical environment (measured by more traffic, more physical disorder, low residential density, and primarily residential neighborhood) would be negatively associated and the social environment (measured by safety and social cohesion) would be positively associated with children's physical activity levels and that these levels would correlate with childhood obesity.
