CORVALLIS - Is suburban life making people overweight? Or could it be that overweight people tend to choose the suburban life?
In a study recently published in the Journal of Regional Science, researchers from Oregon State University found that the relationship between obesity and urban sprawl may be a two-way street.
Economists Andrew Plantinga from OSU's Department of Agricultural and Resource Economics and Stephanie Bernell from OSU's Department of Public Health expanded previous studies that showed that people living in areas of urban sprawl tend to have higher body mass indices. Their analysis suggests that the relationship between obesity and urban sprawl may be due to personal preferences when choosing a home location rather than to direct impacts of the suburban environment on physical activity and weight.
Location, location, location. Research by Plantinga and Bernell suggests that an individual's body weight is a factor determining the desirability of a residential location. They found the relationship between obesity and urban sprawl can be explained by the way people sort themselves by personal preference.
In a follow-up study, Plantinga and Bernell used a national data set to test whether body mass index influences the decisions of adults to locate in counties with a high or low degree of sprawl. To measure body weight, the researchers used data from the U.S. Department of Labor's National Longitudinal Survey of Youth, which has tracked statistics on thousands of individuals since their youth in 1979. The researchers examined many factors, among them ethnicity, gender, age, income, education, marital status and body weight.
"Among people who moved recently, we find that in addition to a high body mass index, being female, younger, and married increases the probability of choosing to reside in a sprawling county," Bernell said.
"In many sprawling areas, distances are too great for people to walk to work or to the store," Plantinga explained. "Transportation infrastructure is often designed for automobiles, with the result that walking and bicycling are impractical and unsafe. The incentives are for people to drive instead of walk. In contrast, in urban neighborhoods like the Pearl District in Portland, Ore., people can walk to work, school, or shopping. In many cases, it's easier to walk to the store than to drive."
Previous studies had suggested that the relationship between obesity and urban sprawl is related to suburban environments that discourage routine physical activity such as walking and biking. However, previous studies did not consider the choices people make in selecting where to live.
"When you select a residential location, you are really choosing a bundle of attributes," Plantinga said. "The house you choose may be near a shopping center or a park, or it may have a three-car garage and a bonus room. The market prices each of these attributes. It follows that individuals, given their income, will choose locations that provide the attributes of greatest value to them. People who value walking will tend to choose walkable neighborhoods. People who do not care for walking will tend not to."
These findings have implications for urban planners and public health officials, according to Plantinga. Many recent planning initiatives include funding for bicycle and pedestrian facilities in order to increase physical activity. However, making communities more exercise-friendly may simply attract people who are predisposed to physical activity.
Plantinga and Bernell's follow-up study, "The Association Between Urban Sprawl and Obesity: Is it a Two-way Street?" is available online on Bernell's homepage.