Science News Online

Week of Jan. 20, 2007; Vol. 171, No. 3

Weighing In on City Planning

Could smart urban design keep people fit and trim?

Ben Harder

Lawrence Frank is no couch potato. Taking full advantage of his

city's compact design, the Vancouver, British Columbia, resident

often bikes to work and walks to stores, restaurants, and museums.

That activity helps him stay fit and trim. But Frank hasn't always

found his penchant for self-propulsion to be practical. He previously

lived in Atlanta, where the city's sprawling layout thwarted his

desire to be physically active as he went about his daily business.

[IMAGE] Metropolitan Atlanta, often called a poster child for urban

sprawl, has undergone rapid geographical expansion as its population

has burgeoned to about 5 million. Studies suggest that urban sprawl

contributes to physical inactivity and obesity.

Getty Images

"There was not much to walk to," says Frank, a professor of urban

planning at the University of British Columbia. For example, he

recalls that there was only one decent restaurant within walking

distance of his old home. Many restaurants and other businesses in

Atlanta cluster in strip malls that stand apart from residential

areas.

In Vancouver, by contrast, Frank's neighborhood contains dozens of

eateries, and he often strolls to and from dinner. "I'm more active

here," he says.

The glaring difference between the two cities' landscapes figures in

Frank's professional life as well as in his personal one. Frank is

part of an emerging area of cross-disciplinary science that's

examining the relationship between the shapes of our cities and the

shapes of our bodies.

He and other researchers have evidence that associates health

problems with urban sprawl, a loose term for humanmade landscapes

characterized by a low density of buildings, dependence on

automobiles, and a separation of residential and commercial areas.

Frank proposes that sprawl discourages physical activity, but some

researchers suggest that people who don't care to exercise choose

suburban life. Besides working to settle that disagreement,

researchers are looking at facets of urban design that may

shortchange health.

As scientists investigate the relationship between sprawl and

obesity, a compact style of city development sometimes called smart

growth might become a tool in the fight for the nation's health.

However, University of Toronto economist Matthew Turner charges that

"a lot of people out there don't like urban sprawl, and those people

are trying to hijack the obesity epidemic to further the smart-growth

agenda [and] change how cities look."

Studying spread

For decades, housing and population growth in U.S. suburban areas

have outpaced those in city centers. Shifts in commuting patterns

reflect the trend toward people residing at a sizable distance from

where they work, shop, and play. According to U.S. Census data, the

average commute lengthened from 22.4 minutes to 25.1 minutes between

1990 and 2000, and the proportion of workers walking or biking to

work dropped by one-quarter.

[IMAGE] TIGHT FIT. Densely built urban areas such as Vancouver's

downtown may encourage pedestrian traffic and promote physical

activity. In contrast, cities of low density, where people depend on

cars to get to stores and other facilities, seem to favor obesity.

Corbis

A few communities buck the national trend. For example, Frank says,

"there is a great deal of new development in Atlanta that is

walkable."

"That said, the overall trend is not in this direction in that region

or most others," he adds. Even "Vancouver is embarking on a massive

road-building program that threatens [to create] sprawl in the

developing parts of this region."

In September 2003, two major studies linked sprawl and obesity. Since

those reports, researchers in fields as disparate as epidemiology and

economics have generated a spate of similarly themed studies.

In the first of the 2003 reports, researchers analyzed data from a

nationwide survey in which each of some 200,000 people reported his

or her residential address, physical activity, body mass, height, and

other health variables. Residents of sprawling cities and counties

tended to weigh more, walk less, and have higher blood pressure than

did people living in compact communities, concluded urban planner

Reid Ewing and his colleagues at the University of Maryland at

College Park's National Center for Smart Growth Research and

Education.

[IMAGE] OBESITY CITY. Infrared satellite images show the rapid

geographical expansion of metropolitan Atlanta. Built-up areas, such

as roads and buildings, appear bluish-white against the red backdrop

of areas dominated by trees and plants.

Frank

In the second study, health psychologist James Sallis of San Diego

State University and his colleagues reported that residents of

"high-walkability" neighborhoods, which have closely packed

residences and a mix of housing and businesses, tended to walk more

and were less likely to be obese than residents of low-walkability

neighborhoods.

In 2004, Frank and his colleagues produced additional connections

among urban form, activity, and obesity. The data on more than 10,500

people in the Atlanta area indicated that the more time a person

spends in a car, the more obese he or she tends to be. But the more

time people spend walking, the less obese they are.

Frank's team, like the other groups, found that areas with

interspersed homes, shops, and offices had fewer obese residents than

did homogeneous residential areas whose residents were of a similar

age, income, and education. Furthermore, neighborhoods with greater

residential density and street plans that facilitate walking from

place to place showed below-average rates of obesity.

The magnitude of the effect wasn't trivial: A typical white male

living in a compact, mixed-use community weighs about 4.5 kilograms

(10 pounds) less than a similar man in a diffuse subdivision

containing nothing but homes, Frank and his colleagues reported.

So far, the dozen strong studies that have probed the relationships

among the urban environment, people's activity, and obesity have all

agreed, says Ewing. "Sprawling places have heavier people," he says.

"There is evidence of an association between the built environment

and obesity."

Cause or coincidence

The evidence for a relationship between physical activity, body

weight, and the environmental characteristics called urban form

"looks compelling," adds Ross Brownson, an epidemiologist at St.

Louis University School of Public Health in Missouri.

But Brownson, Ewing, and others caution that these associations don't

prove that sprawl causes laziness or weight gain. Most of the studies

provide only a snapshot of different people at a single time. Such

studies can't prove that living amid sprawl leads to inactivity; it

may also be that inactive people choose to inhabit areas where

driving is the easiest way to get around.

In other words, people with different health habits and different

propensities to gain weight may sort themselves into different kinds

of neighborhoods.

That's what Turner suggests is going on. Turner conducted a study

that tracked people over time, as some of them moved from one

neighborhood to another. He and his collaborators found no change in

weight associated with moving from a sprawling locale to a dense one,

or vice versa.

"We're the only ones that have tried to distinguish between causation

and sorting... and we find that it's sorting," he says. "The

available facts do not support the conclusion that sprawling

neighborhoods cause weight gain."

Turner's team analyzed data collected over 6 years on more than 5,000

young adults living across the United States. Most of the volunteers

moved at least once during the study. The researchers compared

individuals' weights before and after they moved between communities

with different degrees of sprawl.

To measure sprawl, they used satellite images to calculate the

average distance between residential buildings. They also determined

the average density of nonresidential establishments such as churches

and shops in each volunteer's zip code.

"We're estimating the effect [of sprawl on weight] to be zero or very

close to zero," Turner says. Any weight gain attributable to sprawl,

he says, is at most "a couple of ounces."

The authors released the study as a working paper on Oct. 30, 2006.

Other researchers challenge some of the study's analytical methods,

particularly the way in which Turner's team assessed sprawl and mixed

use. For example, Sallis says, "They assumed that [churches and

retail businesses] were equally dispersed around the zip code." The

study may therefore have inaccurately estimated volunteers' access to

walkable destinations, he says.

Sallis also argues that it could take many years for significant

weight gain to develop after a person moves between dissimilar

neighborhoods. Moreover, the study didn't assess whether volunteers'

degree of physical activity changed when they moved, a measure that

would hint at impending changes in weight.

Still, Sallis says, Turner's longitudinal approach to the issue is

"definitely an advance. We've been wanting studies like this for some

time."

Ewing has also completed a prospective study using a similar set of

data, but he declined to discuss his results with Science News before

the study's publication.

Obesity is not the urban environment's only—nor even necessarily

its most likely—potential health effect, says physician Deborah

Cohen, a health researcher at the RAND Corporation in Santa Monica,

Calif. If a neighborhood's design were to make people less active,

they might eat less to avoid obesity but still miss out on other

health benefits of physical activity, notes Cohen.

"Physical activity is independently important for health, [and] urban

form is important for physical activity," she says.

In 2004, Cohen and Roland Sturm of RAND asked more than 8,000

residents of 38 U.S. communities to list their health problems. The

researchers also assessed the degree of sprawl in each resident's

community.

"People reported more complaints—more health problems—when

they lived in more sprawling areas," Cohen says. The excess of

physical problems such as arthritis linked to sprawl was comparable

to the change that would occur if the entire population suddenly aged

by 4 years, Cohen and Sturm concluded.

Setting and sorting

Frank's latest findings could split the ideological difference. By

surveying people in a variety of neighborhoods, he learned that

people who are less inclined to be active tend to live in less

pedestrian-friendly locales—evidence that people are sorting

themselves. But he also found that, no matter how much people like or

dislike being active, they are more active when they live in compact,

walkable areas than when they live in sprawling neighborhoods.

[IMAGE] THE DISCONNECT. A community's so-called network efficiency

influences its walkability. In an efficient network, such as in the

gridlike neighborhood at left, pedestrians can walk relatively

directly between any two points. The maze of cul-de-sacs at right

forms an inefficient network.

Frank

His study, he says, "demonstrates that both preferences and the

neighborhood in which people live impact their behavior." He

described the findings at a conference in Atlanta on Jan. 19 and

reports them in an upcoming Social Science and Medicine.

The people most at the mercy of sprawl, Ewing suggests, are those who

have limited access to healthy foods and who don't recognize the

importance of fitness.

Children are another group that could be disproportionately affected

by urban design, Frank says.

In two recent studies, Cohen and her collaborators examined the

relationship between adolescent girls' physical activity and specific

aspects of the urban environment. Girls who live near parks and

recreational facilities are more physically active than those whose

neighborhoods contain no such spaces, the researchers found.

They selected a middle school in each of six metropolitan areas

throughout the country. From among the female students attending the

schools, the team randomly selected 1,556 sixth graders.

In one study, the researchers used maps and government records to

locate public parks. On average, 3.5 parks lay within a 1-mile radius

of each volunteer's home. That figure varied from about six parks in

Minneapolis to about one park in Tucson.

The researchers outfitted the girls with pedometerlike devices called

accelerometers, which record motion and can be used to measure the

intensity of physical activity. Each volunteer wore her accelerometer

for 6 consecutive days. During that time, the girls performed, on

average, the metabolic equivalent of 611 minutes of vigorous physical

activity.

The researchers conservatively estimated that each park within a

half-mile of home contributed an extra 17.2 minutes of vigorous

activity per girl over the course of the study. The team reports its

findings in the November 2006 Pediatrics.

"Neighborhood parks are particularly important for adolescents who

are too young to drive," says Diane Catellier, a statistician at the

University of North Carolina at Chapel Hill who collaborated with

Cohen on that study.

In the other study, reported in a 2006 supplement to the Journal of

Physical Activity and Health, Cohen's team used data on the same

girls to show that living in proximity to one's school is also

associated with increased levels of physical activity.

"The overarching message is that the built environment is an enabler

or a disabler of active transportation—of walking," Frank says.

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References:

Cohen, D.A., et al. 2006. Public parks and physical activity among

adolescent girls. Pediatrics 118(November):e1381-e1389. Available at

Cohen, D.A., et al. 2006. Proximity to school and physical activity

among middle school girls: The trial of activity for adolescent girls

study. Journal of Physical Activity and Health 3(Suppl. 1):S129-S138.

Available at

Eid, J., et al... and M.A. Turner. Preprint. Fat City: Questioning

the relationship between urban sprawl and obesity. Working paper.

Available at

Ewing, R., et al. 2003. Relationship between urban sprawl and

physical activity, obesity, and morbidity. American Journal of Health

Promotion 18(September/October):47-57. Available at

Frank, L.D., et al. 2004. Obesity relationships with community

design, physical activity, and time spent in cars. American Journal

of Preventive Medicine 27(August):87-96. Available at

Frank, L.D., et al. In press. Social Science and Medicine.

Saelens, B.E., J.F. Sallis, et al. 2003. Neighborhood-based

differences in physical activity: An environment scale evaluation.

American Journal of Public Health. 93(September):1552-1558. Available

Sturm, R., and D.A. Cohen. 2004. Suburban sprawl and physical and

mental health. Public Health 118(October):488-496. Abstract available

Sources:

Ross C. Brownson

Department of Community Health and Prevention Research Center

Saint Louis University School of Public Health

St. Louis, MO 63104

Diane J. Catellier

University of North Carolina, Chapel Hill

School of Public Health

137 E. Franklin Street, Suite 203

Chapel Hill, NC 27599

Deborah A. Cohen

RAND Corporation

1700 Main Street

Santa Monica, CA 90401

Reid Ewing

National Center for Smart Growth

University of Maryland, College Park

1112J Preinkert Field House

College Park, MD 20742

Lawrence D. Frank

School of Community and Regional Planning

University of British Columbia

1933 West Mall Annex #231

Vancouver, British Columbia V6T 1Z2

Canada

James F. Sallis

Department of Psychology

San Diego State University

3900 5th Avenue, Suite 310

San Diego, CA 92103

Matthew Turner

Department of Economics

University of Toronto

150 Saint George Street

Toronto, Ontario M5S 3G7

Canada

From Science News, Vol. 171, No. 3, Jan. 20, 2007, p. 43.

Copyright (c) 2007 Science Service. All rights reserved.

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