Previous literature suggests that several attributes of walkability are associated with physical activity and obesity (6
) but few studies have examined these associations by neighborhood race and SES (4
). The main findings from the current study indicated that among individuals residing in predominately white or high-SES neighborhoods, a highly walkable neighborhood was associated with lower obesity compared to individuals living in poorly walkable neighborhoods after controlling for demographic variables and investigating possible intermediate variables.
There are three key explanations for these findings. First, national data has shown that whites report more leisure-time physical activity compared to blacks (15
). Thus, individuals living in predominately white neighborhoods may be more likely to observe or socialize with active neighbors and, consequently, be more likely to engage in physical activity in an effort to maintain or lose weight. Prior research has indicated that observing the exercise habits of peers and neighbors may be beneficial for improving individual physical activity behaviors (29–31). In these neighborhoods, a walkable neighborhood environment may promote and increase the likelihood of activity and, subsequently, lower obesity. In contrast, there was no association between neighborhood walkability and obesity among individuals residing in predominately black neighborhoods. This may be due to few individuals inclined to engage in activity, regardless of the environment. One reason for less activity may be concern for neighborhood safety (29, 32, 33). A study conducted in Los Angeles and Louisiana determined that blacks more often perceived their neighborhood as unsafe and that this neighborhood perception was most strongly associated with less frequent utilitarian walking (16
). Among HANDLS participants, the perception of crime was more often reported among individuals residing in highly walkable, predominately black neighborhoods, which suggests that crime may negate any effect of a walkable neighborhood.
Second, individuals living in high-SES neighborhoods may utilize cars more often for daily transportation than individuals living in low-SES neighborhoods. Indeed, 64% of individuals residing in high-SES neighborhoods reported using a car as their main mode of transportation compared to 36% of individuals in low-SES neighborhoods. Therefore, high-SES neighborhoods that are conducive to walking for transportation and physical activity may facilitate more activity and, subsequently, lower obesity. The measures used to capture this activity may not have been sensitive enough. In contrast, individuals living in low-SES neighborhoods may walk for transportation out of necessity. Indeed, there was no significant association between walkability and obesity after controlling for mode of transportation. Fifty-one percent of individuals in low-SES neighborhoods reported either walking or using public transportation most often and those who reported walking or using public transportation had significantly lower BMI compared to car users.
Third, there may be other population-level factors that influence obesity but were not accounted for in these analyses. For example, variation between neighborhoods in the availability of healthy food may impact obesity status in this population. Previous work conducted in Baltimore found that predominately black and lower-income neighborhoods and the supermarkets located within had significantly lower healthy food availability compared to predominately white and higher-income neighborhoods (17
). In addition, lower availability of healthy foods was associated with a lower quality dietary pattern; the association was insignificant after adjusting for race (18
). Given increases in total energy consumption (19
) and the low prevalence of physical activity among adults (20
), it is important to understand how neighborhood walkability and healthy food availability interact and influence obesity in neighborhoods of varying characteristics.
Although few studies have examined associations between walkability and obesity stratified by neighborhood characteristics, the literature has been consistent in that, even after controlling for individual-level SES, living in an economically deprived neighborhood increases the likelihood of being obese or having a high BMI (35–37). Similar associations for neighborhood race have been documented (21
), although the literature has been less consistent. Two studies found no association between neighborhood race and obesity (37, 38) while one study found that neighborhood racial isolation was significantly associated with obesity among black residents only (22
). This research suggests that the effects of neighborhood-level race and SES may be at least partially mediated through differential access to health-promoting or health-constraining environments and resources (23
). Indeed, previous literature indicates that physical activity resources are less likely to be located in lower-SES and minority neighborhoods (4
). In addition, one study determined that residing in high- versus low-walkability neighborhoods increased weekly physical activity but found no difference by neighborhood income (6
). Despite these previous and current findings, some caution in interpretation should be noted. Adjusting for individual-level demographics may, in fact, be an over-adjustment and result in overestimation if these demographic variables are antecedent to the exposure and not true confounders.
Sampling is paramount when conducting observational studies intended to determine the effects of neighborhood walkability. An almost universal problem for these types of studies is overcoming neighborhood self-selection where individuals choose or are limited to neighborhoods with certain attributes (e.g. poor walkability) based on individual characteristics (e.g. low-SES) that are likely related to the outcome (24
). Rather than using regression methods to “control for” the effects of SES, a few recent studies have attempted to overcome these effects by sampling high- and low-walkability neighborhoods with the caveat that these neighborhoods included a homogenous population with respect to SES and geographic location (42, 43). Although measures of walkability differed in these studies, both found positive associations for physical activity and/or utilitarian walking. The authors of the latter study note, though, that walkability was not meaningfully related to overall mean miles walked or increased physical activity (25
). To assess the effect of neighborhood income, a more recent study recruited participants from high- vs. low-walkability and high- vs. low-SES neighborhoods (6
). Again, participants were more active if they lived in high-walkability neighborhoods but, in contrast to the current results, there was no difference by neighborhood SES. Although the parent study for the current analysis was not designed to sample neighborhoods based on level of walkability, the results do suggest that the effect of neighborhood walkability on obesity differs by neighborhood characteristics.
Major strengths of this study were objective measures of the pedestrian environment and individual-level outcome measures. The PEDS audit measured the walking environment for transportation and physical activity at the micro-scale, thus, captured information that is not available through national databases; confirmatory factor analysis was used to reduce random measurement error in each PEDS item. Additionally, obesity was objectively measured which is the preferred measurement method for large epidemiologic studies. Furthermore, the stratified sampling design allowed for associations to be compared by neighborhood characteristics.
Nevertheless, this study had some limitations. First, the study was cross-sectional which limits the ability to make causal statements about observed associations. Second, census tract boundaries were used to approximate neighborhoods, which creates the potential for measurement error in environmental attributes located in a participant’s neighborhood. Nevertheless, the use of census tracts is common in the field since these boundaries are created to represent a homogeneous area (26
). Third, the length of exposure to certain neighborhood characteristics is unknown, thus, associations may not reflect the walkability characteristics measured in this study. However, it is unlikely that mobile individuals move to drastically resource-different neighborhoods due to financial limitations and social preferences (45). Fourth, physical activity was self-reported for only on a small number of HANDLS participants. Nevertheless, since the physical activity measure did not capture utilitarian walking, an important factor in this line of research, a separate transportation question was used as a proxy for information on walking habits. Finally, the use of multilevel level models makes conclusions on possible intermediate variables difficult given that the variance structures of the neighborhood- and individual-level variables are different; caution should be taken when interpreting potential mediating pathways.
The literature base on walkability and obesity is still in its infancy. Although earlier work is promising, there are methodological issues that should be challenged in future work. First, the environmental determinants of obesity are numerous and few studies have incorporated comprehensive models to account for both energy expenditure and energy intake (i.e., environmental supports for physical activity and healthy dietary intake). Second, most previous studies were cross-sectional which severely limits the ability to imply causal associations; experimental or longitudinal studies are needed. Third, formative research should be used to establish the most appropriate neighborhood spatial scale for varying demographic and geographic populations. Fourth, few studies have explored walkability beyond the scope of neighborhoods (e.g., workplace). Finally, improvements in the conceptualization of walkability are warranted. Numerous attributes of walkability have been associated with obesity; future work should further define walkability for varying populations and geographic areas.
In conclusion, neighborhood walkability may partially explain racial and socioeconomic disparities in obesity. A thorough understanding of the underlying mechanisms in which these associations operate is justified. At the very least, individual physical activity recommendations and weight-management guidelines should recognize neighborhood walkability as an important enabler or inhibitor to meeting these guidelines.