ARTICLE IN BRIEF
The odds of incident cognitive impairment were 18 percent higher among residents of the stroke belt than among non-belt residents after adjusting for strong independent predictors of cognitive decline, including age, sex, and education level, according to a new study.
Findings of a 50 percent higher stroke mortality rate in eight Southern states identified as the “stroke belt” — Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Tennessee — were first reported in 1965, and they have remained consistently higher in subsequent analyses.
Now a new study shows that the same areas have a higher incidence of cognitive impairment compared to other regions of the country.
The odds of incident cognitive impairment were 18 percent higher among residents of the stroke belt than among non-belt residents after adjusting for strong independent predictors of cognitive decline, including age, sex, and education level, the study concluded. The differences held when race was factored in as well.
“The study is the first known documentation of higher incident cognitive impairment in the Stroke Belt region of the United States than in the rest of the nation,” the study authors wrote in the May 26 online edition of Annals of Neurology.
The study's lead author Virginia Wadley, PhD, associate professor of medicine at the University of Alabama at Birmingham, told Neurology Today in an e-mail that “the causes of the stroke belt — and now this overlapping region of incident cognitive impairment — have not been adequately identified.”
She noted, however, that “our results are consistent with the assumption that there are shared risk factors for the adverse outcomes of stroke and cognitive decline, and the study's ongoing results may help to delineate factors underlying geographic -disparities in stroke and cognitive decline.”
THE STROKE BELT
The results of this latest study are based on data collected as part of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, an epidemiological study following a cohort of adults from across the US for stroke and cognitive decline. From 2002 to 2007 the study enrolled 30,239 residents aged 45 or older, including 16,934 from the eight stroke belt states and 13, 305 from the other 40 contiguous states and the District of Columbia.
The participants' demographic profiles and medical histories were obtained during a computer-assisted telephone interview. There were also home visits to collect body fat measurements, blood and urine samples, and an electrocardiogram. Participants were followed with telephone interviews twice a year to check for hospitalization and if stroke was reported, medical records were obtained by the study physician.tParticipants' global cognitive status was assessed annually by telephone with the Six-Item Screener (SIS) and every two years with fluency and recall tasks.
This latest analysis of REGARDS data included 23,913 people (56 percent from the Stroke Belt) who reported no history of stroke and were cognitively intact at enrollment, meaning they had a score of at least 5 out of 6 on the SIS. The analysis included data acquired through -October 2010.
Incident cognitive impairment occurred, over an average interval of four years, among 8.1 percent of US adults aged 45 years and older in this study, the researchers reported. Those living in the stroke belt were 18 percent more likely to have cognitive impairment than people elsewhere. In all, there were elevated rates of cognitive impairment in six of eight stroke belt states (75 percent) compared to 10 of 23 (43.5 percent) non-belt states, including Washington, DC.
When impairment at the two most recent consecutive assessments was required for incident case definition, the adjusted odds ratio increased to 40 percent higher risk in the stroke belt region, suggesting an even greater regional disparity in persisting impairment, the researchers reported.
RISK FACTORS CITED
The researchers considered other variables, besides place of residence, to see what bearing they had on cognitive status. Blacks were at higher risk than whites for cognitive impairment. It's been well documented that African-Americans are at increased risk for stroke and death from stroke. Education also came into play. The likelihood of cognitive impairment was 2.27 times higher for study participants who did not graduate from high school compared to college grads.
The researchers noted that the same risk factors for stroke — hypertension, diabetes, and metabolic syndrome — also increase the risk for cognitive impairment.
“Future work should examine the influence of migration pattern, urban/rural residence, life course socioeconomic factors, and educational quality in relation to cognitive decline,” the investigators wrote.
They noted that “pinpointing regional patterns in the contribution of modifiable risk factors to incident cognitive impairment will allow for geographically concentrated prevention and intervention efforts.”
NON-TRADITIONAL RISK FACTORS
Dr. Wadley told Neurology Today that her team is doing follow-up research to examine the role of traditional risk factors, such as hypertension and smoking, as well as more novel risk factors for cognitive decline, including environmental exposures and inflammation biomarkers.
The published report addressed some possible limitations of the study, including the use of the short SIS tool to determine cognitive decline.
“It is a screening instrument with limitations inherent to all screening measures, including ambiguity surrounding interpretation of scores at the cut point between intact and impaired and a likely lack of sensitivity to subtle cognitive changes,” Dr. Wadley said in the e-mail. “We have, however, demonstrated that this approach is a reasonable way of detecting global cognitive status changes in a study of this scope.”
The researchers also noted the results could be skewed due to moderate response rates and response bias, though they noted that participation rates were “comparable to those achieved by similar population-based studies.”
David S. Knopman, MD, professor of neurology at the Mayo Clinic in Rochester, MN, told Neurology Today that while the SIS screening tool does have limitations compared to the more detailed Mini-Mental Status Exam, for instance, it is an appropriate choice for large -epidemiological studies.
Dr. Knopman said he believed this latest study underscores not the importance of geographic location per se, “but rather the socioeconomic and health behavior status of the people who happen to live in those places.”
“Culture and education play a big role in health behavior,” he said. “People with higher socioeconomic standing are less likely to smoke cigarettes, more likely to treat their hypertension and diabetes, more likely to adhere to their medications, more likely to see a physician, and less likely to be obese,” he said.
Dr. Knopman said that while doing demographic analyses are important for health care planning purposes, “we in a sense already know what the public health challenges are.”
“We know we have to have young people watching their weight and having their blood pressure checked and getting screened for diabetes early on,” he said. “By the time overweight, diabetic, hypertensive people are in early midlife their health is already a problem.”