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Howard G, Anderson R, Johnson NJ, Sorlie P, Russell G, Howard VJ

Evaluation of social status as a contributing factor to the stroke belt region of the United States

Stroke (May) 28:936-940 1997

Source: American Heart Association News release

DALLAS, May 13 -- For decades it's been known that stroke, the nation's third deadliest disease, takes its highest toll in the Southeastern United States. Now researchers say this stroke belt has a “buckle” -- a zone-within-a-zone that has stroke death rates “substantially higher” than the stroke belt itself and twice as high as the rest of the country.

Reporting in the May issue of the American Heart Association journal Stroke, the scientists identify the “buckle” as coastal plain sectors of North Carolina, South Carolina and Georgia. In this 153-county area, the new study shows, stroke deaths are 2.1 times higher than the rate of the nation overall among people ages 35 to 54 and 1.7 times greater for people between 55 and 74.

George Howard, Dr.P.H., the report’s lead author, estimates that this “localized bulge” represents “more than 1,000 extra deaths a year from stroke.” He says the nation should be “outraged” by this loss of life. “If any single other factor, such as an environmental element or a food additive, was causing this many deaths every year, there would be a major outcry.”

In the larger area traditionally recognized as making up the stroke belt, stroke deaths were 1.3 times higher than in the rest of the nation for those ages 35 to 54 and 55 to 74, the study showed. The five other stroke belt states are Tennessee, Arkansas, Louisiana, Mississippi and Alabama.

Surprisingly, Howard and his colleagues found only a slim statistical connection between stroke death rates and socioeconomic status (SES) as measured by income and education levels. SES, acknowledged to be lower than the national average in much of the stroke belt, has been suggested by other studies as a cause for the region’s increased stroke death toll. But the researchers report finding that “SES does not appear to be a major contributor to the excess [stroke] mortality” in the Southeastern United States. They calculate that less than 16 percent of the excess stroke risk found in the stroke belt or buckle is explained by the contribution of SES.

Previous comparisons of SES and stroke in the Southeast have been based on studies that involve collecting information on areas or groups of people, not individuals, Howard says. “This is the first study to my knowledge that has data on the SES of individuals and confirmation of death of individuals, and correlated those two.”

The investigators at Bowman Gray School of Medicine in Winston-Salem, N.C., used information from the National Longitudinal Mortality Study, which matches (via Social Security numbers) data from death certificates with information on income, occupation and education collected from regular Census Bureau unemployment reports. The data from 1979-89 covered some 400,000 participants who were observed for an average of 8.4 years.

Reasons for the excess stroke deaths in the stroke belt, and particularly, the buckle, remain a mystery, notes Howard, professor of biostatistics and epidemiology at Bowman Gray.

“Actually,” he says, “it could be a wide range of things.” Risk could be inherent in the geography through components like the drinking water or soil-borne elements that end up in food, for example. “Or it could be regional differences in lifestyle choices, irrespective of the individual’s SES. It could be habits like smoking more cigarettes or eating more fat and salt. The bottom line is, we still don’t know,” he says. “Despite the fact that this phenomenon has been here for half a century, no one really understands why it’s there. And there’s very little funding to search for the answers.”

Although the new findings appear to rule out SES as a potential cause of the excess stroke deaths, Howard says it’s clear SES is still a risk factor for stroke, especially among African-Americans in the region, whose risk of stroke is 1.5 times higher than whites’.

The excess stroke deaths, the Bowman Gray team believes, are related to factors that often accompany low SES that also increase stroke risk -- smoking, high blood pressure, diabetes, obesity and physical inactivity. “The lower average SES of the Southeastern United States has long been considered a possible explanatory cause for the stroke belt, with SES acting to raise risk through an association with traditional stroke risk factors or an association between SES and access to health care.”

Adds Howard: “Being poor isn’t bad for you per se. It’s what you do that’s bad for you.”

A shortcoming of their study, the authors admit, was a lack of data on those traditional risk factors. “Because of this absence, the role of these factors [smoking, diabetes, hypertension, etc.] in the pathway between SES and stroke mortality could not be assessed,” they write.

The authors say their observation of a higher stroke risk in the three-state coastal plain shouldn’t diminish interest in finding causes of stroke in the entire belt but should focus on “a region meriting truly extreme concern.” They continue:

“The consistency and magnitude of the excess stroke mortality in the stroke buckle region should draw the attention of health-care providers and public policy administrator and motivate an even greater effort to identify the underlying causes of the excess stroke mortality in this region.” Howard’s co-authors are Roger Anderson, Ph.D.; Gregory Russell, M.S.; and Virginia J. Howard, M.S.P.H., all of Bowman Gray; and Norman J. Johnson, Ph.D., of the U.S. Census Bureau; and Paul Sorlie, Ph.D., of the National Heart, Lung, and Blood Institute.

Stroke is one of five journals published in Dallas by the American Heart Association.