Research articleGeographic Distribution of Diagnosed Diabetes in the U.S.: A Diabetes Belt
Introduction
The American “stroke belt,” defined in terms of a contiguous group of states with high age-adjusted stroke mortality rates, was first identified in the mid-1960s.1 The states that define the stroke belt are Alabama, Arkansas, Georgia, Indiana, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, and Virginia. The stroke belt's identification contributed to further study of the etiology of stroke and to helping target interventions to high-risk states.2, 3
Diabetes is similar to stroke in that it is strongly affected by behavioral, cultural, and environmental factors clustered and overlaid on genetic susceptibility. However, U.S. geographic patterns of diabetes have not been as specifically characterized in the manner that stroke has been. Identification of areas of high prevalence of diabetes could have an impact on understanding of diabetes.
Recently, the CDC produced estimates of the prevalence of diagnosed diabetes for every U.S. county or county equivalent.4 Figure 1 displays a map of the estimated prevalence of diagnosed diabetes for 2007, with counties/county equivalents shaded to represent the percentage of the population with diagnosed diabetes, dividing the counties into quintiles. This map suggested to the authors the existence of a “diabetes belt,” to be precisely defined later, probably not previously characterized because of the lack of county-level diabetes surveillance data.
This paper (1) proposes a definition of the diabetes belt; (2) examines how residents of that belt compare with residents of the rest of the country in demographics and prevalence of selected risk factors for diabetes and in the association of demographics and risk factors associated with diabetes; and (3) calculates the fraction of the excess risk of diabetes associated with residence in the diabetes belt that is attributable to selected risk factors.
Section snippets
Data Source
Data from the 2007 and 2008 Behavioral Risk Factor Surveillance System (BRFSS) were used. The BRFSS is a state-based system of health surveys that annually assesses key behavioral risk factors and chronic conditions among non-institutionalized U.S. adults aged ≥18 years. Nationally, the median state response rates for BRFSS were 50.6% (2007) and 49.8% (2008). The BRFSS collects county-level data but, because of sample-size limitations, most analyses are done at a state or national level. Using
Results
Details of the spatial smoothing are not reported, for brevity. However, the results of this smoothing appear in Figure 2. Figure 2 displays a map of the 644 counties that define the diabetes belt. This belt includes portions of the states of Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, and West Virginia, as well as the entire state of Mississippi. The prevalence of diabetes in the diabetes belt was
Discussion
To the authors' knowledge, this paper is the first to identify a diabetes belt. Both diabetes and stroke belts are primarily located in the southeastern U.S. However, differences exist. Much of West Virginia is in the diabetes belt, but not in the stroke belt. Indiana is part of the stroke belt but contains no diabetes belt counties.
Public health is often carried out at a county level. Identifying a diabetes belt via counties allows policymakers to identify regions where need is greatest,
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