SAN FRANCISCO – People who live in "walkable" neighborhoods have a 15% lower rate of diabetes, compared with those who live in areas that require reliance on automobile transportation, a large Canadian study found.
"It’s become clear that the way we build and design our cities has an important impact on our health," Dr. Gillian L. Booth said at the annual scientific sessions of the American Diabetes Association. "Neighborhoods that were designed for pedestrian use are more conducive for walking. They tend to be older areas that are more densely populated, have more street connections, and are zoned in a way that retail and other services are embedded within residential areas. That means that there are more walkable destinations."
Dr. Gillian L. Booth
Sprawling suburban communities, on the other hand, tend to be more sparsely populated, and have fewer connections between streets, "and the zoning is such that retail and other services are separated and far away from where people live, thus increasing one’s reliance on automobiles for transportation," continued Dr. Booth, an endocrinologist and research scientist at St. Michael’s Hospital and the University of Toronto "There’s mounting literature that these types of neighborhood features are associated with lower rates of walking and physical activity and higher levels of obesity. They also lead to more time spent in cars, which in itself has been linked to a higher risk of becoming obese."
Until recently, there have been few prospective studies looking at neighborhood design and the development of diabetes. Limitations to previous studies include the fact that those who prefer to live in one neighborhood over another may differ systematically from those who choose to live in other neighborhoods. To account for this, Dr. Booth and her associates used Inverse Probability of Treatment Weighting to create balanced groups of adults aged 30-64 years living in high- and low-walkability areas.
"We asked the question, are individuals living in more walkable areas at a lower risk of developing diabetes? If this is true, does that still hold after we account for other confounders?" These confounders included age, sex, presence of comorbidities, previous hypertension, stroke, health care use, socioeconomic status, and ethnicity.
The study area consisted of 15 Canadian municipalities, including Toronto, which have a combined population of more than 7 million people. The researchers used anonymous health data from provincial databases of people who were free of diabetes and living in high- or low-walkability neighborhoods in April 2002, and followed them through March 2012 for the development of diabetes. The investigators excluded people with a prior diagnosis of diabetes.
Dr. Booth and her associates identified new cases of diabetes via the Ontario Diabetes Database, an electronic registry based on hospital and physician service claims. The walkability index was based on four features: population density (number of residents per square kilometer); residential density (number of dwellings per square kilometer); street connectivity (number of intersections per square kilometer), and walkable destinations (the number of stores and services within a 10-minute walk).
The study population consisted of 958,567 Canadian residents; their mean age was 49 years and 49% were male. Over the 10-year follow-up period, 90,922 new cases of diabetes were observed, for an incidence rate of 1.03/100 person-years. The researchers observed a 15% lower diabetes incidence among those living in the highest-walkability areas, compared with the lowest-walkability areas, in all study regions (hazard ratio of 0.85). They observed similar findings when they stratified people by income (HR of 0.86 and 0.82 for lower- and higher-income areas, respectively) and immigration status (HR of 0.85 among long-term residents and 0.87 among those who had been Canadian citizens for fewer than 10 years).
She concluded that high neighborhood walkability appears to be protective against the development of diabetes in young and middle-aged urban populations. "This suggests that changes in zoning, urban planning, and design that promote walking and other forms of active transportation may help to curb the ongoing rise in obesity and diabetes," she said. "Further research is needed to understand the full impact that such interventions will have."
The study was funded by the Canadian Institutes of Health Research. Dr. Booth said that she had no relevant financial conflicts to disclose.