More than 18 million people in the U.S. have been diagnosed with diabetes, which costs an estimated $174 billion annually. Typically, local public health agencies carry out the initiatives to manage and prevent this chronic disease, but because prevalence figures are generally given on national and state levels, local workers cannot gain the traction—and funding—to rein in rates in their areas.

A new study drills down to the county level, revealing wide disparities within states and striking national patterns. "We're extremely excited about the county level," says Lawrence Barker, associate director for science at the U.S. Centers for Disease Control and Prevention (CDC) Division of Diabetes Translation.

Many of the counties with the highest rates of diagnosed diabetes—higher than 11.2 percent of the population compared with the national average of 8.5 percent—are concentrated in 15 states and form an area the study's authors have labeled the "diabetes belt" (after the so-called "stroke belt" that described U.S. Southeast in the 1960s).

"We've known for many years that there was a lot of diabetes in the Southeast," Barker says. But the new analysis, based on data from the self-reported national phone survey called the Behavioral Risk Factor Surveillance System (BRFSS), confirmed that the disease has a distinctive geographical distribution. The map and findings will be published in the April 2011 issue of the American Journal of Preventive Medicine.

The pattern of disease distribution is not a simple slice—nor does it follow the stroke belt. The diabetes belt touches states as far north as Ohio and Pennsylvania and as far west as Texas. But overall averages for many of these outlying states would not reveal the plights of their few high-prevalence counties.

State numbers have long been misleading, says Ali Mokdad, who works at the University of Washington School of Medicine's Institute for Health Metrics and Evaluation (IHME) in Seattle and was not involved in the new study." A state number masks a lot of the variation in the state," he says. Similar county-level work that he has done showed that although states such as Colorado can have low levels of diabetes overall (7.1 percent), the average can be misleading because super-low counties (such as Pitkin County's 4.5 percent) can cover up those with sky-high rates (such as Crowley County's 14.1 percent).

With new local data, however, the 644 counties in the diabetes belt match up to known risk factors for the disease, including: a high obesity rate (32.9 percent versus 26.1 percent nationally); sedentary lifestyles (30.6 percent versus 24.8 percent); lower education levels (24.1 percent with college degrees versus 34.3 percent) and more non-Hispanic blacks (23.8 percent versus 8.6 percent).

Even people who live in diabetes belt counties and whose demographics would not otherwise raise any red flags for being high risk for diabetes (for example, young, white and not obese) are more likely to have been diagnosed with the condition, Barker says.

The good news, Barker and his colleagues report, is that about 30 percent of the extra risk faced by people in diabetes belt counties is tied to lifestyle choices that can be changed. "If people led more active lifestyles, then the new cases of diabetes would be smaller," he said. Modifying people's risky behavior should bring the diabetes numbers closer to national averages—"eventually," Barker says.

Barker, who is based in Georgia, one of the states that has many counties in the diabetes belt, suggests that one of the reasons for the striking distribution might have to do with the area's economic history. "These are regions and areas that were once heavily agricultural," he says. But as the economy has shifted away from farming—especially the more local, labor-intensive agriculture of the early and mid-20th century—to more sedentary jobs, people might not have adjusted their diets to compensate for smaller daily calorie requirements and are "continuing to eat the same way they used to," he speculates.

The 15 states that have counties in the diabetes belt are Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, Virginia and West Virginia. Belt counties, however, are unevenly distributed among those states on the list, ranging from a few in Ohio and Texas to the majority of Alabama's counties—and every one in Mississippi.

Not every county with rates of diagnosed diabetes above 11.2 percent lies within the newly designated region—some are as far afield as Washington and Montana. But regardless of location, the new information should help local officials have a better understanding of their areas' problems—and make a better case for additional resources for prevention and management programs. "When you give the [local] number itself, that's more of a motivation for action," Mokdad says.

Mokdad and some of his colleagues at IHME hope to provide even more county-level data by combining the phone survey information with findings from smaller, national clinical studies. Their findings, published in 2010 in Population Health Metrics, include additional risk factors such as the prevalence of fast-food restaurants, in addition to data about how well people's diabetes are being managed. "That's the next wave of what we need to provide to these counties," he says.

But Barker calls attention back to the national diagnosed diabetes rate of 8.5, suggesting it is not exactly the best target to have in mind—even for counties that currently have the highest prevalence rates. "While diabetes is more of a problem in the diabetes belt, it's a problem everywhere, and we shouldn't overlook that."