Neighborhood Design for Walking and Biking

Background

Neighborhood designs often relate to physical activity and to BMI.

Purpose

Does neighborhood walkability/bikeability relate to BMI and obesity risk and does moderate-to-vigorous physical activity (MVPA) account for some of the relationship?

Methods

Census 2000 provided walkability/bikeability measures—block group proportions of workers who walk or bike to work, housing age, and population density—and National Health and Nutrition Examination Study (NHANES 2003–2006) provided MVPA accelerometer measures. Regression analyses (2011–2012) adjusted for geographic clustering and multiple control variables.

Results

Greater density and older housing were associated with lower male BMI in bivariate analyses, but there were no density and housing age effects in multivariate models. For women, greater proportions of neighborhood workers who walk to work (M=0.02) and more MVPA was associated with lower BMI and lower obesity risk. For men, greater proportions of workers who bike to work (M=0.004) and more MVPA was associated with lower BMI and obesity risk. For both effects, MVPA partially mediated the relationships between walkability/bikeability and BMI. If such associations are causal, doubling walk and bike-to-work proportions (to 0.04 and 0.008) would have −0.3 and −0.33 effects on the average BMIs of adult women and men living in the neighborhood. This equates to 1.5 pounds for a 64-inch-tall woman and 2.3 pounds for a 69-inch-tall man.

Conclusions

Although walking/biking to work is rare in the U.S., greater proportions of such workers in neighborhoods relate to lower weight and higher MVPA. Bikeability merits greater attention as a modifiable activity-friendliness factor, particularly for men.

Introduction

A growing body of work relates activity-friendly neighborhood environmental designs to measured physical activity, or separately, to healthier adult BMIs.1, 2 The underlying conceptualization is that environmental supports for walking or biking will enable residents to be more active and thereby sustain healthy BMIs. Yet few neighborhood studies actually include both physical activity and BMI in the same model. The present research relates activity-friendly neighborhood environmental indicators, including novel evidence of bikeability, to objective measures of physical activity and BMI.

Many studies have assessed how “walkability”—neighborhood design features that support walking—relates to walking. These measures typically include aspects of the “3Ds” of walkability: population density, land-use diversity, and pedestrian-friendly street design.³ The present study employs four census indicators of activity-friendly environments that are available for all U.S. communities, have received substantial empirical support,4, 5 and could guide community interventions. These include older neighborhoods, greater density, and greater proportions of workers who walk or bike to work.

Older neighborhoods have many modifiable 3D design features⁶ that might encourage active transportation⁷ and healthier weight8, 9: high population densities; diverse destinations; and pleasant, tree-shaded sidewalks.6, 10 Higher population density creates the critical mass needed to provide neighborhood destinations such as transit stops and restaurants and has been related to more physical activity11, 12 and lower BMI.8, 13, 14, 15, 16, 17, 18 Land-use diversity, such as homes near workplaces,8, 9 brings desired destinations within walking distance. Diversity is defined in various ways¹⁹ and is often related to healthier weight.8, 17, 18, 19, 20, 21, 22

Few studies of neighborhood design and weight include “bikeability” (i.e., cyclist-friendly design), although bikeable environments may support physical activities for many, not just for cyclists. Biking is more likely in environments that offer density,12, 23 diversity,²³ activity-friendly design features (e.g., lower speeds on roads²³); or a combination of the 3Ds.²⁴ These studies generally, but not universally,²⁵ suggest that bikeability is similar to walkability. Bikeable environments may also include additional features, such as bike signage and traffic lights,²³ bike lanes,²⁶ or road-separated bike paths,²⁷ bike lane connectivity,²⁸ and nearby sports and park spaces29, 30 or natural amenities.¹² Further, bicycling involves longer trips than walking. Thus, bikeable and walkable environments may be sufficiently distinct to have unique relationships with residents' physical activity and BMI.

Walkability/bikeability often relates to physical activity and/or BMI, but not to both outcomes in the same model. For example, in Baltimore and Seattle, 3D walkability related to more adult MVPA and, separately, to less overweight/obesity risk.³¹ In Atlanta, the 3Ds related to more walking and, separately, to less risk of overweight and obesity, for white men only.³² For National Health and Nutrition Examination Study (NHANES) 1988–1994 data, county walkability related to self-reported walking and, separately, to measured weight.³³

One study in Ghent, Belgium, tested whether activity mediated the relationship between walkability and self-reported BMI in low- and high-walkability neighborhoods.³⁴ Surprisingly, walkability was not related to BMI but higher accelerometer-measured MVPA was related to lower BMI. The authors argued that MVPA mediated the relationship between walkability and weight. The present study tests for mediation in the U.S., where walkability/bikeability and active transportation are lower.35, 36 Specifically, the current paper examines (1) whether walkability/bikeability relates to BMI and obesity risk; and (2) whether this relationship diminishes when MVPA is included in the analysis, suggesting a causal role for MVPA.