Knowledge of racial and geographic patterns in stroke risk factors may provide useful information for public health interventions. Ultimately, the goal is to identify targets for interventions in specific population groups that may reduce the disparities in stroke incidence and consequently the burden of stroke in all populations. The FSRS is a summary index incorporating “traditional” stroke risk factors and estimates the predicted stroke incidence over 10 years. In this national study, geographic differences in the average FSRS across regions were small. This suggests that only a small portion of the 50% higher stroke mortality in these regions is driven by the “traditional” risk factors comprising the FSRS. Because hypertension is the strongest stroke risk factor we expected that hypertension would play a major role in differences in stroke fatality. However, geographic differences in diabetes were substantially larger than differences in hypertension (defined by medication use). Findings suggest that interventions to reduce geographic disparities in diabetes, including optimizing prevention, diagnosis and treatment, may hold promise for reducing geographic disparities in stroke mortality.
While geographic differences in diabetes prevalence were the largest differences seen among stroke risk factors, this association differed in race/sex strata, all of whom share the higher stroke mortality of the stroke belt and buckle. There were small differences in the prevalence of diabetes in white women, diabetes was not more common in the stroke belt than the rest of the nation among black men, and differences in diabetes prevalence by region were largest in black women. In the Behavioral Risk Factor Surveillance System, self-reported diabetes was highest in the southeastern US states in 2001, with the stroke belt states of Alabama ranking 1st
(10.5%), Mississippi 2nd
(10.3%), South Carolina 4th
(9.4%), Arkansas 6th
(8.9%), Louisiana 7th
(8.5%), Tennessee 11th
(8.3%), Georgia 22nd
(7.7%), and North Carolina 23rd
Most papers on causes of the stroke belt have largely assumed that the cause is higher stroke incidence in this region 5, 6
. Our findings of relatively small differences in FSRF by region, and of similar FSRS in the ‘higher risk’ stroke buckle than stroke belt raise a hypothesis that stroke case fatality might play a substantial role. While components of the FSRS might influence case fatality, other factors not addressed in our analysis, such as poverty, access to care and non-traditional risk factors also need to be considered. Studies such as REGARDS, which follow a large geographically dispersed cohort, will help to answer these questions.
While geographic differences in the FSRS were relatively small and influenced by selected component risk factors, differences in the FSRS between whites and blacks were substantially larger, with differences in many of the component risk factors, in particular diabetes and hypertension. These racial disparities have been previously described 22, 23
including higher systolic blood pressure in blacks than whites (by approximately 5 mmHg), even in the setting of higher prevalence of antihypertensive medication use 24
. It has been suggested that higher prevalences of diabetes, hypertension and other risk factors contribute to racial disparities in stroke risk 22, 25
but few prospective studies are available with sufficient numbers of African-American and white participants to address this question. Follow-up in the REGARDS cohort will help clarify this.
Our findings extend previous reports on geographic variation in hypertension from the NHANES 26–28
. In NHANES III 26, 27
there was a slightly higher prevalence of hypertension in the southeast for white men (27% versus 24%), white women (22% versus 21%), and black men (35% versus 33%), with a more substantial difference for black women (35% versus 28%). In further analysis assessing age groups (40–59 and 60–79 years), hypertension was more prevalent in the southeast in 7 of 8 age-race-gender strata; however, these differences were only statistically significant among black men aged 40–59 and white men aged 40–59 28
. We are not aware of other studies providing a true regional comparison of hypertension prevalence. Because the focus of this paper was overall differences in the FSRS which considers use of antihypertensive medications and the average systolic blood pressure, we focused on these parameters rather than hypertension, per se
. Anti-hypertensive medication use was more common in the stroke belt than the rest of the nation for both whites and African-Americans. However, the pattern of blood pressure was not consistent, with whites having a higher blood pressure in the stroke belt (but not buckle) than the rest of the nation, and African-Americans having lower systolic blood pressure in the stroke buckle (but not belt) than the rest of the nation. Thus, there is a mixed picture regarding geographic variations in hypertension and blood pressure, with NHANES showing trends for higher blood pressure in the Southeast, and REGARDS showing higher use of antihypertensive medications but an inconsistent pattern in measured blood pressure. The NHANES reports used a more broad definition of Southeast, which may explain some of these differences. We have reported detailed analyses of correlates of regional and racial differences in hypertension elsewhere 24
Few population-based data are available on prevalence of atrial fibrillation and LVH by region and race. Case-control studies and hospital series suggest that atrial fibrillation is less prevalent and may be less strongly associated with stroke risk among blacks than whites in the U.S.29, 30
. In one study of African-Americans (2.7% with previous stroke; 68% with hypertension), 49% of participants had LVH by echocardiogram, and this was associated with an increased risk of magnetic resonance imaging-documented stroke and white matter disease 31
The strengths and weaknesses of this study merit discussion. Study examinations were conducted in participants’ homes by a large number of examiners rather than in a limited number of field sites as in most similar studies. While substantial training and standardization efforts were undertaken18
, these cannot replicate the quality of field center-based epidemiologic studies. This shortcoming is offset by the advantages of a large nationally-based sample with oversampling of African-Americans and residents of the stroke belt and buckle, enabling optimal assessment of geographic and racial disparities. As with all epidemiologic studies, participation rates are a concern. We conservatively estimated a 40% participation rate in REGARDS, which compares favorably to other epidemiologic studies. The current analysis included 23,940 participants without stroke or TIA, with 41% African-Americans. Thus these results are more precise than other studies that included far fewer subjects 7, 28
. Unlike the BRFSS 21
, REGARDS measured most components of the FSRS rather than relying on self-reported data, providing better reliability for the FSRS. About 8% of participants were missing at least one component of the FSRS, leading to exclusion of these individuals. While we relied on self-reported cerebrovascular disease as a selection criterion for the current analysis, any impact of potential misclassification on findings would be small given the sample size and rarity of disease. As in other population-based studies, REGARDS is limited to non-institutionalized individuals who had a telephone, which may restrict generalizability. Finally, the FSRS has not been validated in African-Americans, therefore it may not be an optimal tool for assessing stroke mortality risk in this group.
In summary, we observed only modest differences in the FSRS between the stroke belt or stroke buckle compared to the rest of the US, and differences were mostly driven by geographic differences in diabetes and hypertension. Interventions to reduce geographic disparities in these factors may be promising for reducing geographic disparities in stroke mortality. However, given the small regional differences in the FSRS, it seems unlikely that the increased stroke mortality in the Southeast is due solely to differences in traditional risk factors that comprise the score. Follow up data from this study will examine these questions and the role of other risk factors. Conversely, we observed the expected racial differences in hypertension, diabetes, atrial fibrillation and LVH that could contribute to racial differences in stroke risk. These disparities offer hypotheses for interventions that might reduce racial disparities in stroke mortality.