Jan 30, 2006
Obesity is the most serious public health problem confronting America today. Obese and overweight Americans face elevated risks of chronic illness and disability. As the obesity epidemic worsens, researchers are zeroing in on environmental factors that may contribute to the problem or, conversely, help to prevent it. It is increasingly clear that neighborhoods play an important role in stimulating exercise and reducing the risk of obesity. To shed more light on this connection, a series of RAND studies has examined how neighborhood characteristics affect physical activity.
Neighborhood parks play an important role in promoting exercise. In the first systematic evaluation of neighborhood use of public parks, a RAND team led by researcher Deborah Cohen assessed activities in 12 Los Angeles public parks. The researchers surveyed park users as well as a sample of the local population. They found that living near a park was associated with engaging in more exercise. This may not be because people were exercising at the park—in fact, the most frequent activity observed in the park was sitting. However, more than three-quarters of users lived a mile or less from the park (see Figure 1), and most walked to the park from their homes, thus getting exercise by walking there and back. People—especially adults and seniors—were more likely to exercise at parks that had areas for moderate exercise, such as tracks, walking paths, and trails. Having a park near one's home was more important than the size of the park itself—people were more likely to use their neighborhood park even if a larger park was just a few miles away. The researchers also noted that, in all age groups, males were much more likely than females to use neighborhood parks.
Girls pose a particular concern because their physical activity is known to decrease as they progress through adolescence, raising their risk of weight gain. A related study by Cohen and colleagues examined park use and physical activity among adolescent girls. The study examined exercise patterns among more than 1,500 sixth-grade girls in six U.S. cities. It also counted the average number of public parks within a one-mile radius of the girls' homes. The study found that adolescent girls who live within one-half mile of a public park are more physically active than other girls. Higher levels of physical activity were seen among girls who lived near small parks, playgrounds, walking paths, and running tracks.
|City||% of Accessible School Playgrounds or Exercise Facilities on Weekends|
|New Orleans (before Hurricane Katrina)||23|
School playgrounds that are accessible to children on weekends may also promote exercise. Focusing on the same sample of sixth-grade girls, researchers visited 407 school playgrounds within a half-mile radius of the homes of the girls. Results showed that 66 percent of the schools were unlocked on weekends, although the percentage of available school facilities varied substantially among different cities (see the table). But only 57 percent of schools both were unlocked and had accessible facilities, such as playgrounds, athletic fields, basketball courts, and paved playing areas. The majority of locked and inaccessible playgrounds were in poor and minority neighborhoods.
Although the study did not find a relationship between school accessibility and increased weekend physical activity rates, the number of locked schools was associated with significantly higher body mass index for girls (body mass index is a mathematical formula representing weight relative to height that can be used to determine whether a person is overweight or underweight). The fact that girls with a higher body mass index tended to live in areas with locked schools could signal that the girls live in a more stressful, high-crime area, which would create incentives for them to remain indoors, or in a neighborhood with access to stores that sell unhealthy food. Stress itself is associated with obesity due to higher secretions of the stress hormone cortisol, which increases fat deposits.
Other neighborhood features also influence levels of physical activity. A RAND study led by Rob Boer examined the relationship between neighborhood features and walking trips in ten U.S. cities. The analysis found that business diversity was associated with walking trips. Having four or more different types of businesses in a neighborhood significantly increased the number of walking trips among residents. This is probably true because of added convenience: Residents are able to accomplish multiple routine errands in a single walking trip and thus may drive less. A greater number of four-way intersections was also associated with more walking. The effects of housing density were mixed. Neighborhood age, availability of parking, and block length were not significantly associated with walking.
Aside from their physical configuration, neighborhoods can influence body weight and the risk of obesity in other ways. Cohen and colleagues also studied the effect of neighborhood social cohesion on the weight gain of adolescents. They found that children who lived in close-knit neighborhoods were less likely to be overweight than children who did not. Researchers analyzed responses from 3,000 households including 807 adolescents in 65 neighborhoods in the Los Angeles area. Close-knit neighborhoods were defined as those with the greatest degree of "collective efficacy," a measurement that characterizes social cohesion. Such neighborhoods contain adults who children look up to, people willing to help their neighbors, neighbors who get along, adults who take active steps to ensure that children are safe, neighbors who share the same values, adults who will intervene if a youngster is defacing property with graffiti, and adults who will scold a child showing disrespect. In neighborhoods that lacked these features, adolescents were more likely to be overweight, even after controlling for other factors (see Figure 2). Although the analysis did not identify causes, the researchers speculated that close-knit neighborhoods might be associated with lower levels of stress and could also promote increased physical activity by making neighborhoods feel safer and more "walkable."
Taken collectively, these studies underscore that neighborhoods exert a powerful effect on residents' physical activity and thus that neighborhood design should be considered a public health issue. Communities would profit by taking steps to create and maintain public facilities and spaces that are known to promote exercise. These steps can include
Researchers need to learn more about neighborhood factors that promote or discourage physical activity, especially among younger people. Expanding understanding about how neighborhood characteristics can influence obesity should help identify effective ways to address the problem. In addition, researchers need a clearer understanding of the mechanisms through which neighborhood social cohesion can influence body weight. If collective efficacy truly prevents excessive weight gain, then future interventions to control weight may need to move beyond individual prescriptions aimed at diet and exercise and address the social environment at the community level.