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James F. Sallis, PhD, a psychology professor at San Diego State University, lives only two blocks from a commercial district and three blocks from a grocery store, so he's able to run errands on foot. The neighborhood's many walking paths and bike trails mean that he can also exercise and get out into nature whenever he wants.

Many Americans, especially those in poor communities, aren't so lucky. Whether they live in car-centric suburbs or impoverished inner cities, the built environment often makes it hard for them to stay healthy. Ubiquitous fast-food restaurants, sprawl, substandard housing and other such factors contribute to obesity, asthma and other health problems and to health disparities.

In recent research, Sallis has found that small changes in the physical environment can make big differences in healthy behavior. He's just one of many psychologists who are turning their attention to the once-overlooked role that the built environment plays in health. And they're not just studying the problem: They're also suggesting ways to redesign places to promote--rather than prevent--healthy behavior.

A walk in the park

Suburban sprawl contributes heavily to obesity and other ills, says Sallis, who directs the Active Living Research Program at San Diego State University.

"Walkable neighborhoods were the norm for thousands of years," he says. "Since the 1940s, however, most of the development in the United States has been based on the assumption that we drive everywhere."

In a 2006 article in the Journal of the American Planning Association (Vol. 72, No. 1, pages 75-87), Sallis and his co-authors--including city planner Lawrence Frank, PhD, at the University of British Columbia--reveal just how unhealthy suburban sprawl can be. The authors used a "walkability" index that measures residential density, land use mix, retail floor area and the presence of streets that connect well with each other rather than meandering like suburban lanes.

The researchers discovered that even small increases in walkability had an impact, says Sallis, noting that the study was commissioned by the King County, Washington, government. A five percent increase in walkability, for example, was associated with residents spending about a half-hour more each week walking or biking to get where they needed to go and having a quarter-point lower body mass index.

But it's not just a matter of obesity and the chronic health problems associated with it, adds Sallis. Walking more means driving less, which reduces pollution and lowers asthma rates.

What's needed, he says, are changes in zoning, development and transportation regulations to encourage developers to put housing, workplaces and schools within walking or biking distance of one another. In addition, city planners can make space for parks, paths and sidewalks to encourage exercise and outdoor recreation.

"Putting a person who loves to drive in a walkable neighborhood may not stop their driving," says Sallis, who has shared his ideas with governments, corporations and other researchers around the world. "But if a person who wants to be active can't find an affordable, walkable neighborhood to move into, then they're prevented from being as active as they want to be."

A walk in the park can be good exercise, of course, but researchers are also finding that exposure to the outdoors can help people cope with stress.

For instance, in a 2003 study in Environment and Behavior (Vol. 35, No. 3, pages 311-330), Nancy M. Wells, PhD, an assistant professor of design and environmental analysis at Cornell's College of Human Ecology, and Gary W. Evans, PhD, the Elizabeth Lee Vincent Professor in the same department, examined the effect of being able to see natural views from the window, having a yard made of grass rather than dirt or concrete and living among houseplants. They found that children with lots of nature nearby coped better with stressors like divorce, a grandparent's death or bullying than children with less natural environments.

Although it's still not clear why, Wells has two theories: Nature may draw people outside, where they meet others and form social support networks. Or perhaps nature helps people think more clearly and cope more effectively, she says, pointing to the large body of literature on the "restorative" effects of nature. Nature, Wells explains, offers a restful mini-vacation to minds fatigued by focused concentration.

What is clear are the design implications, says Wells, a frequent speaker at conferences on residential design and health. Place children's desks near windows and plant trees where they can be seen from inside, she suggests. At the community level, access to parks and what Wells calls "green natural corridors" between places can help.

Making healthy easy

The built environment doesn't just have an impact on people's activity levels. It also affects their eating behavior, says psychology professor Kelly D. Brownell, PhD, director of the Rudd Center for Food Policy and Obesity at Yale University. Researchers are shifting from thinking of obesity from the standpoint of personal responsibility to a more systemic perspective, says Brownell, who co-authored Food Fight: The Inside Story of the Food Industry, America's Obesity Crisis, and What We Can Do About It (McGraw-Hill, 2003).

The absence of supermarkets in many neighborhoods is just one factor that contributes to what Brownell calls a "toxic environment."

In fact, Brownell explains, one of the strongest predictors of whether low-income people will eat a healthy diet full of fruits and vegetables is their proximity to a supermarket. Unfortunately, the number of supermarkets in poor urban areas has dropped steadily over the years. "In inner-city Los Angeles, for example, there were something like 30 full-service supermarkets three decades ago," he says. "Now there are about five."

The reason for the decline? Companies are afraid to build stores in high-crime areas, says Brownell. And companies may believe that low-income consumers have less to spend than those in wealthier communities, he notes. Fast-food joints are taking up the supermarket's slack, with predictably unhealthy results, adds Brownell.

There are ways to turn back the tide, however. Tax incentives could bring supermarkets back to areas that need them, says Brownell, and zoning restrictions could keep fast-food restaurants away from schools or even limit the number of such establishments in a given community.

"In the case of both physical activity and nutrition, the environment has made unhealthy behavior the default," says Brownell.

Some environments are even more literally toxic, such as housing with lead paint or pesticides, says Susan Saegert, PhD, director of the Center for Human Environments and an environmental psychology professor at the City University of New York Graduate Center.

The daily struggles of living in substandard housing can also leave people without enough energy to take care of themselves, says Saegert, who served as principal editor of a 2005 report from APA's Task Force on Urban Psychology called "Toward an Urban Psychology: Research, Action, and Policy."

"People who run asthma-management programs often report that parents are too overwhelmed by the process of daily life to keep up with the program," says Saegert, noting that bad housing is usually accompanied by mold, crime, poor public services and other stressors.

Efforts to improve housing typically focus on single problems and typically fail, says Saegert. In a 2003 article in the American Journal of Public Health (Vol. 93, No. 9, pages 1,471-1,477), she and several co-authors reviewed the literature on housing-related public-health interventions. They found that only 14 percent could be judged extremely successful.

What works are approaches that tackle the complex interplay among the physical environment, behavior and health, Saegert says.

That's just the approach she and others took when the city of Denver asked for help in the 1980s. Together, she and a team of architects and city planners developed a plan to bring high-quality housing into the city, increase walkability and add running paths. To bring nature to the urban environment, they transformed what was a dirty ditch filled with shopping carts into a river.

That kind of ecological approach is more useful than focusing on individual responsibility, says Saegert.

"All the other problems associated with the worst housing overwhelm the behavioral change required to keep up with dust mite prevention, cockroach prevention or other health-oriented interventions," says Saegert. "If you want to help the people with the greatest housing and health burdens, then you need to concentrate on improving the ecology of the areas."

 Rebecca A. Clay is a writer in Washington, D.C.