摘要：Objectives. We evaluated the association between the county sprawl index, a measure of residential density and street accessibility, and physical activity and body mass index (BMI). Methods. We conducted a multilevel cross-sectional analysis in a sample of Nurses’ Health Study participants living throughout the United States in 2000 to 2001 (n = 136 592). Results. In analyses adjusted for age, smoking status, race, and husband’s education, a 1-SD (25.7) increase in the county sprawl index (indicating a denser, more compact county) was associated with a 0.13 kilograms per meters squared (95% confidence interval [CI] = −0.18, −0.07) lower BMI and 0.41 (95% CI = 0.17, 0.65) more metabolic equivalent (MET) hours per week of total physical activity, 0.26 (95% CI = 0.19, 0.33) more MET hours per week of walking, and 0.47 (95% CI = 0.34, 0.59) more MET hours per week of walking, bicycling, jogging, and running. We detected potential effect modification for age, previous disease status, husband’s education level (a proxy for socioeconomic status), and race. Conclusions. Our results suggest that living in a dense, compact county may be conducive to higher levels of physical activity and lower BMI in women. The obesity epidemic in the United States is well documented, 1,2 with estimates that 35.5% of adult women are obese. 3 Only 60.4% of US women meet 2008 Department of Health and Human Services physical activity guidelines. 4 Overweight and obesity are linked with numerous health outcomes, including cardiovascular diseases, arthritis, and stroke. 5,6 Obesity has a multifactorial etiology, influenced by genetics, behavior, and environmental factors. 7 Interventions at the environmental or neighborhood level, therefore, plausibly could change obesity-related behaviors and alter the distribution of overweight and obesity. A growing literature links physical activity and obesity to the built environment. 8 The built environment is defined as land-use patterns, transportation systems, and design features that provide opportunities for travel and physical activity. 9,10 Attributes of the built environment, such as density, street connectivity, and land-use mix, have consistently been associated with increased walking and overall physical activity, as well as decreased body mass index (BMI). 6,8,11–17 These factors create opportunities for walking, because homes, stores, and other destinations are closer, and influence access to recreational physical activity. 18,19 Aspects of the built environment may have greater impact on women than on men for several reasons. Women bear a disproportionate burden for many of the outcomes associated with the built environment: they are more likely to be obese 3 and less likely to meet physical activity guidelines. 4,20 Women drive to places to exercise less frequently than do men and are more likely to walk for leisure activity, so walking in the neighborhood may be an important source of exercise. 21,22 If the relationships between the built environment and health are truly causal, then interventions to improve the neighborhood built environment could have great impacts on the health of women. Urban sprawl is defined as a process in which the “spread of development across the landscape far outpaces population growth.” 23 (p3) It is characterized by 4 dimensions: low residential density; rigidly separated homes, shops, and workplaces; roads with large blocks and poor access; and a lack of well-defined activity centers. These factors are thought to lead to decreased ability to walk from place to place and a lack of transportation choices. We used both individual health-related factors and county-level factors to examine the association between urban sprawl, physical activity, and BMI in a large sample of women living throughout the continental United States.
