In the 'Stroke Belt,' Erosion of Memory Is More Likely Too
By PAM BELLUCK
People in a large area of the American South have long been known to have more strokes and to be more likely to die from them than people living elsewhere in the country.
Now, a large national study suggests the so-called stroke belt may have another troubling health distinction. Researchers have found that Southerners there also are more likely to experience a decline in cognitive ability over several years - specifically, problems with memory and orientation.
The differences to date in the continuing study are not large: Of nearly
24,000 participants, 1,090 in eight stroke-belt states showed signs of cognitive decline after four years, compared with 847 people in 40 other states.But the geographic difference persisted even after the researchers adjusted for factors - like age, sex, race and education - that might influence the result. The most recent data from the study were published in Annals of Neurology.
None of the people with cognitive decline in the study had had detectable strokes. But some experts believe their memory problems and other mental issues could be related to the same underlying risk factors, including lifestyle patterns that contribute to hypertension, high cholesterol, diabetes and obesity.
Is it the fried food beloved by Southerners? Limited access to doctors? Too little exercise? Researchers are investigating those and other possible causes. Some experts also suggest that the participants could have had small, undetectable strokes that subtly affected brain function.
"This should be a very strong alarm signal," said Dr. Gustavo C. Roman, who leads the neuroepidemiology section of the American Academy of Neurology and was not involved in the study. The finding suggests that "if you want to keep your marbles, you need to control your blood pressure, excessive weight and other risk factors for stroke."
Dr. Kenneth Langa, a professor of internal medicine at University of Michigan who was not involved in the research, said the size of the study and the geographic diversity, encompassing 1,588 of the country's
3,000 counties, made the findings powerful.They could also be instructive because, while there is currently almost no treatment for memory problems later in life, there are effective ways of combating or preventing many causes of stroke. "Pinning down this relationship between hypertension, diabetes, physical inactivity and the effects on the brain" could help people learn to protect their mental capacities for longer, Dr. Langa said.
Experts do not know exactly why more strokes occur in a region stretching across Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Tennessee (sometimes additional Southern states are included in the stroke belt). Financed by two federal health agencies as part of a broader study of stroke and health, the new research followed non-Hispanic blacks and whites age 45 and older for about four years.
At the beginning of the study, the participants, assessed in a detailed phone interview and home visit, had experienced no strokes or cognitive problems. Each year, researchers conducted telephone interviews, asking the subjects to recall words and demonstrate knowledge of the day, week and year. Every two years, there were longer telephone assessments with more extensive word-recall tests and tasks like naming items in a category - animals, for example.
As of October 2010, 8.2 percent of stroke-belt participants showed signs of cognitive decline; 8 percent of participants in other areas did. The small difference was nonetheless significant in such a large study, experts said.
"The difference is actually larger than those two numbers seem to suggest," said George Howard, the study's principal investigator and chairman of the biostatistics department at the University of Alabama at Birmingham. By chance, the particular Southerners in the study had qualities that should have made them less vulnerable to cognitive problems, not more so. They were younger and more of them were women, compared with study subjects elsewhere, and fewer were African-American, a group that is more prone to strokes.
"If region didn't make any difference, the South should have been significantly less likely to be declining" in the study results, Dr. Howard said.
In both stroke-belt and non-stroke-belt groups, older age, less education, and being African-American were associated with increased chances of cognitive decline. But even when those factors were accounted for, residents of the stroke belt still were 18 percent more likely to show impairment.
"These effects are so large, it overcomes these differences in the population," Dr. Howard said. Most memory and orientation problems detected in the four years were subtle, he added, although a few cases were more severe.
Virginia Wadley, the study's lead author and an associate professor of medicine at the University of Alabama at Birmingham, and her colleagues are now looking for possible causes, including genetic predisposition, nutrition, smoking, exercise, hypertension, high cholesterol, obesity, diabetes, emotional or work-related stress and environmental factors like air quality. "It's likely a mixed bag," Dr. Wadley said.
Many of these are also risk factors for stroke, and some experts say it is possible that participants could have suffered what Dr. Howard called "undiagnosed teeny-weeny strokes."
Dr. Langa said problems like high blood pressure and diabetes are likely to be "affecting blood flow to the brain, even if it's not causing a visible stroke. An undersupply of blood can also cause problems with brain cells that lead to cognitive decline."
But silent strokes probably cannot explain all participants' memory and orientation problems, the researchers said. Some subjects may have budding dementia, age-related memory loss, or a combination.
"Those behaviors that prevent stroke likely will prevent some but not all of the things that cause cognitive decline," said Dr. Joseph P. Broderick, chairman of neurology at the University of Cincinnati Neuroscience Institute, who was not involved in the study. "If you buy a car and you take great care of it, it still ain't the same 15 years later. But if you don't ever change the oil and your basic engine grinds down, in five years you can't drive it and it won't last very long."
Dr. Roman, who also directs the Nantz National Alzheimer Center at Methodist Neurological Institute in Houston, said the cycle might begin with cognitive decline and then lead to stroke, not the other way around. "If you have lower cognitive function," he said, "maybe you don't care anymore about taking your blood pressure pill" to prevent stroke, which could then cause further memory impairment.
Dr. Broderick cautioned that study may be missing more severe cases of mental impairment, because "you may not get people who don't have a phone, are homeless, very poor."
"This is not just a problem for the stroke belt, it's a problem for the country," he said. "I have some issues with trying to focus attention on just one area, rather than people in the country who fit that high-risk group."
Dr. Howard and Dr. Wadley, both Southerners, acknowledged that the new data can be misinterpreted.
"One of the things we are concerned about is, it does sort of reinforce every negative stereotype about the South, that there are these slow hicks down here," Dr. Howard said. "The first question is, is there a problem? Unfortunately, as a Southerner, the answer is yes. If we can get to why it exists, then we can get to what to do to change it."