More Walkability Means Less Obesity, Diabetes Over Time

Miriam E Tucker

May 24, 2016

Neighborhood walkability was associated with lower risks for obesity and diabetes in the first-ever study to assess the links prospectively.

Findings from the Ontario-based 11-year study were published online May 24 in the Journal of the American Medical Association by Maria I Creatore, PhD, of St Michael's Hospital, Toronto, and colleagues.

The investigators defined "walkability" based on four components: population density, residential building density, number of walkable destinations such as stores or services, and street connectivity.

They found that overall trends for obesity, overweight, and diabetes varied depending on the walkability of their neighborhoods even more strongly than they had anticipated.

"We actually expected that the rates of overweight and obesity incidence would keep going up, but we were pleasantly surprised to see that those rates were actually stable over time in the most walkable neighborhoods," senior author Gillian L Booth, MD, from St Michael's Hospital, told Medscape Medical News.

On the flip side, however, "In the less walkable neighborhoods, the rates of overweight and obesity were continuing to go up," she said.

And while diabetes incidence was stabilizing in most areas, those rates were actually falling in the most walkable neighborhoods.

First Prospective Study of This Relationship

Other studies that have looked at the relationship between neighborhood walkability, levels of physical activity, and rates of diabetes and obesity — including one from Dr Booth's group in 2014 — have all been cross-sectional, whereas this is the first to examine the issue over time.

"Once you're able to look prospectively at future disease risk, it's a much more powerful message. We were able to show that people who live in highly walkable neighborhoods have a lower likelihood of becoming obese and of developing diabetes in the future," Dr Booth said, adding that the current study is also much larger than her group's previous one.

An accompanying editorial states that the new study provides "further large-scale and longitudinal support for the hypothesis that urban-design choices promoting pedestrian activity are associated with greater engagement in active transport (walking and cycling), lower prevalence of overweight/obesity, and lower diabetes incidence at the population level."

And as such, the editorialists — Andrew G Rundle, DrPH, of the Mailman School of Public Health, Columbia University, New York, and Steven B Heymsfield, MD, of Pennington Biomedical Research Center, Baton Rouge, Louisiana — predict the work "will make a prominent contribution to the research base that informs the urban-design and health-policy debates for years to come."

Walkability and Weight

The study involved an analysis of annual provincial healthcare data for approximately three million residents per year during 2001–2012 and biennial Canadian Community Health Survey (about 5500 per cycle) statistics for adults aged 30 to 64 years living in Southern Ontario cities during the same time period.

Neighborhood walkability was derived from a validated index with standardized scores ranging from 0 to 100, with higher scores indicating more walkability. Neighborhoods were ranked and classified into quintiles from lowest (quintile 1) to highest (quintile 5) walkability.

Annual prevalence of overweight, obesity, and diabetes incidence were all adjusted for age, sex, area income, and ethnicity. The databases did not specify type of diabetes.

Of the total 8793 residential neighborhoods in the study area, 8777 were included in the analysis. Overall, 32,767 individuals participated in the Canadian Community Health Survey between 2001 and 2012 and met inclusion criteria, with sample sizes ranging from 4878 to 6165 per cycle.

The most walkable neighborhoods had a lower adjusted prevalence of overweight and obesity at all time points, 43.3% for the top quintile vs 53.5% for the bottom (P < .001).

The obesity prevalence increased significantly in the lower three quintiles of walkability, from 5.4% in 2001 to 8.8% in 2012 (= .003), while overweight and obesity prevalence did not change significantly in the top two walkability quintiles (P = .20).

More Walkability, Less Diabetes

The analysis of diabetes incidence showed temporal patterns similar to those seen for overweight and obesity. After the same adjustments, the diabetes incidence — ie, new cases — was lowest in the most walkable neighborhoods throughout the study period.

In fact, the adjusted annual diabetes incidence dropped significantly in the highest two walkability quintile areas, from 8.7 to 7.6 per 1000 people in quintile 4 and from 7.7 to 6.2 per 1000 in quintile 5.

In contrast, diabetes incidence in the lower walkability neighborhoods remained unchanged from 2001 to 2012 (P = .20). By 2012, the adjusted diabetes incidence was 1.7 per 1000 persons lower in the highest- vs lowest-walkability neighborhoods (P = .001).

Sensitivity analyses showed that walkability was inversely related to diabetes incidence in neighborhoods of all income levels, even including the poorest.

At all time points, residents in the most walkable neighborhoods had higher rates of daily walking or cycling, used more public transit, and drove less often compared with those in the least walkable areas.

However, there was no association between neighborhood walkability and other health behaviors such as fruit and vegetable consumption or smoking. Primary-care use — universally available in Canada — was similar across walkability quintiles (median two visits in the previous year).

Other Factors at Play?

In their editorial, Drs Rundle and Heymsfield caution that the study defines walkability "from purely an urban-design perspective and did not consider social-environment issues such as pedestrian safety, crime, displeasing aesthetic conditions, and physical disorder as contributing to neighborhood walkability."

These other characteristics, they point out, "may interact with, or perhaps overwhelm, urban-design features that support pedestrian activity," noting that in New York City, for example, high-poverty neighborhoods may be just as walkable as wealthier areas yet have more crime, noise, sidewalk trash, and other characteristics that could deter pedestrian activity.

Dr Booth acknowledged that although her group found a benefit with walkability even in the poorest areas, this was a limitation of her study.

"We didn't measure all of those things. This is one piece, but there may be other policy interventions that need to happen in communities to enable people to take advantage of their neighborhoods and have a more favorable outcome."

Drs Rundle and Heymsfield also note that although randomized studies firmly establishing causality would be difficult to carry out, alternative future investigations might confirm and extend the current findings, such as taking advantage of new communities built with the intent of promoting physical activity or following people over time to see whether their physical-activity patterns and health outcomes change as their neighborhoods change.

According to Dr Booth, "A lot more work obviously needs to be done. Cities are evolving, and there's a lot of interest from a policy level to make changes. I think we need to be evaluating what these changes mean in terms of health.…Think about the potential if you could also address some of these other social factors that may be discouraging people from walking."

Dr Booth and her coauthors have no relevant financial relationships. Dr Heymsfield reports membership on the MediFast Advisory Board. Dr Rundle reports membership in the American Institute for Architects (AIA) Design and Health Research Consortium, which receives expense reimbursement from AIA for travel to an annual meeting and provides resources to the consortium for collaborative work; and reports being a consultant for the WELL Building Institute, which certifies buildings and real estate developments as meeting certain health-related criteria. The WELL Building Institute is associated with Delos Living, a company that builds "wellness"-designed buildings.

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JAMA. Published online May 24, 2016. Article, Editorial

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