We hypothesized that residents’ perceptions of the safety of their neighborhoods would be associated with BMI. Analyses using instrumental variables models confirmed this hypothesis, through the finding that the BMI of residents who perceived their neighborhood as unsafe was 2.81 kg/m2 higher than was the BMI of those who perceived their neighborhood as safe after adjusting for individual sociodemographic and clinical characteristics and neighborhood SES. These findings were robust to our sensitivity analyses. Previous literature, which has found mixed association between perceived neighborhood safety and obesity, may have been limited by endogeneity bias. After accounting for this potential bias in our analyses, we identified a significant negative association between perceived neighborhood safety and obesity. Future cross-sectional analyses to study the association between neighborhood characteristics and health should consider the possibility of endogeneity bias and address it through appropriate methods.
Among residents who perceived their neighborhoods as unsafe, BMI was 2.81 kg/m2
higher than for those who perceived their neighborhoods as safe, corresponding to a 7.7 kilogram weight increase for a person 1.65 meters tall. The magnitude of this BMI increase is comparable to or higher than the changes in BMI observed in other studies of individual or neighborhood characteristics and BMI. Two notable studies, focused on neighborhood characteristics and individual eating patterns, found similar associations. After adjusting for other factors, including individual SES, mean BMI was 1.51 kg/m2
higher (approximately 4.1 kilograms for a 1.65-meter individual), in a very low SES area compared with a very high SES area.13
Compared with persons who consumed a healthy diet, those persons whose diets consisted mainly of white bread had an annual increase in BMI of 0.05 kg/m2
and those persons whose diets comprised mainly meat and potatoes had a 0.25 kg/m2
annual increase in BMI.63
In this analysis, we have focused on the “subjective” perception of safety rather than on other indicators of public safety that might be viewed as “objective,” such as crime rates and neighborhood physical disorder. Although these physical hazards may contribute to perceived neighborhood safety, there is limited literature on the association of crime rates or other hazards and either BMI or obesity. Two recent studies found that higher levels of neighborhood disorder and neighborhood psychosocial hazards (composed of indicators of neighborhood social and physical disorganization, physical safety, and economic deprivation) were associated with higher BMI and higher rates of obesity in adults.64,65
The paucity of published studies on the association between health outcomes such as BMI and crime rates and other physical and social hazards may be because of limitations of the available data, among them inconsistent reporting of crime and other neighborhood exposures across geographic units, different data sources, and overall quality of the data.
There are several reasons why the links between perceived neighborhood safety and obesity may be important to researchers, policymakers, and clinicians. Perceived neighborhood safety appears to incorporate the measurable physical and social hazards described above and may reflect other important factors that can influence obesity, among them a lack of resources in areas widely perceived as unsafe. Perceived neighborhood safety may influence residents’ health behaviors and may have physiologic effects that influence levels of stress hormones contributing to deleterious outcomes, such as dysregulation of blood pressure and blood glucose. Asking residents about the safety of their neighborhoods is a relatively simple method for identifying at-risk environments and persons at particularly high risk for obesity in those settings.
There are some potential limitations to these analyses. One caveat regarding the use of instrumental variables is that the estimates usually generalize only to the marginal population.66
In our analyses, however, the marginal population consists of individuals for whom experience of household crime or neighborhood collective efficacy would change their perception of neighborhood safety. If most individuals are likely to fall into this category, the estimates ought to apply quite broadly. Another potential limitation of any instrumental variables model is the assumption that the instruments do not directly affect the outcome57-60
; otherwise, the estimates may lead to over- or understating the association. Although this possibility cannot be completely excluded, all the statistical tests of validity supported the assumption that the instruments—experience of crime and neighborhood collective efficacy—were excludable, that is, not directly associated with BMI after controlling for perception of neighborhood safety. One potential concern might be that, conceptually, collective efficacy could be associated directly with BMI. To our knowledge, no study has evaluated collective efficacy and perceived neighborhood safety together in relation to BMI. We have found 1 earlier study suggesting, without controlling for perceived safety, an association of collective efficacy and BMI in adolescents16
; previous work with adults has not found a similar direct association of collective efficacy and BMI.36
A strength of the instrumental variables model is that it allows perceived neighborhood safety to act as a mediator between collective efficacy and BMI.
The results of these cross-sectional analyses of data from 1 large metropolitan city, with a high proportion of first-generation Latino immigrants, may not generalize to many other areas in the United States. However, given recent demographic shifts in many large US cities, these findings may have important implications for other urban areas with emerging immigrant populations. Additionally, census-derived characterizations of neighborhoods may not accurately reflect the social and physical environment thought to be contributing to individual health and behaviors. However, previous LA FANS data suggests that respondents’ reports of the size and boundaries of their neighborhoods are highly correlated with census-tract definitions of neighborhood size.67
Additional qualitative and longitudinal studies are needed to better understand how neighborhood exposures may influence the health and behaviors of residents.
The study also uses self-reported weight and height. Recent literature on self-report suggests that height is overestimated and weight underestimated and that this reporting varies by race/ethnicity.68
For these analyses, the underestimation of BMI would likely result in an underestimate of the association seen between perceived neighborhood safety and BMI, and any bias introduced is unlikely to differ by perceived neighborhood safety. The study does control for race/ethnicity and neighborhood SES, which may minimize these potential biases.
Last, we used a general definition of perceived safety and did not have details about specific features of neighborhoods that contributed to safety. The heterogeneous findings of previous studies may be because of endogeneity bias or the use of definitions of perceived neighborhood safety that did not capture true resident perceptions of neighborhood safety. Another possibility is that there were gender differences in perceived neighborhood safety. Single-equation analyses were conducted using an interaction term between perceived safety and gender. The single equation, without controlling for endogeneity, found no association between perceived safety and BMI for men and found only a marginal association for women, which suggests endogeneity bias may influence both sexes. There was insufficient power to perform the analyses using instrumental variables, either with an interaction term or using stratified samples.
Our findings suggest a need to consider alternate model specifications that can reduce confounding and endogeneity bias, and allow for more accurate detection of important neighborhood influences on obesity. In addition, efforts to change the behavior of individuals may be countered by neighborhood disorganization and perceived hazards, which promote weight gain or deter weight loss. Clinicians who provide counseling and treatment options to overweight or obese patients may need to consider the conditions in which their patients live and their patients’ perceptions of their neighborhoods. These findings also suggest that clinical and public health interventions aimed at reducing the obesity epidemic may need to improve coping mechanisms, promote behavior modification that facilitates healthier dietary choices and reduces stress, and encourage patient engagement in community-level efforts to reduce physical and psychosocial hazards in their residential neighborhoods.
Critical components of policy efforts and intervention design to reduce the burden of obesity may need to include understanding the following: why residents perceive their neighborhoods as unsafe; how these perceptions may influence physiologic measures of stress, health-related behaviors such as diet and physical activity, and both short- and long-term health outcomes; and whether these effects are reversible in the setting of greater perceived neighborhood safety. The identification of nontraditional influences on obesity suggests that a broader range of solutions must be sought to reduce rates of obesity in many communities. These solutions need to promote less stressful, more secure neighborhood environments through the coordinated efforts of urban planners, law enforcement personnel, elected officials, and community advocates, in addition to individuals affected by obesity and their health care providers.