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High blood pressure, diabetes, atrial fibrillation, and heart disease account for half of black-white stroke disparity

REGARDS Study Identifies Stroke Risk Factors That Account for Half of Racial Disparity

By Peggy Noonan

February 29, 2012

  • Summary: Stroke deaths have dropped dramatically in recent years, but a black-white racial disparity remains. High blood pressure, diabetes, atrial fibrillation, and heart disease were found to be responsible for about half of this disparity, but the other half remains a mystery.
  • Reading time is approximately 6-8 minutes

Although the total number of stroke deaths in the U.S. declined by more than 50 percent between 1978 and 2006, significant racial disparities in stroke deaths remain.

A goal set by the U.S. Department of Health and Human Services aimed to eliminate health disparities by 2010 but efforts to accomplish that goal have been “strikingly unsuccessful,” say the coauthors of a new study, Traditional Risk Factors as the Underlying Cause of Racial Disparities in Stroke: Lessons From the Half-Full (Empty?) Glass.

The researchers used data from REGARDS (REasons for Geographic and Racial Differences in Stroke), a national, population-based, longitudinal study of more than 30,239 black and white volunteers aged 45 or older in 48 U.S. states, says the study’s lead author George Howard, DrPH, professor of biostatistics at the University of Alabama at Birmingham and REGARDS co-principal investigator. The study “oversampled” blacks and residents of the southeastern Stroke Belt states (Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Tennessee) such that 42% of study participants were black and 56% of study participants were residents of the Stroke Belt.

The researchers focused on the black-white disparity because it is the largest racial disparity in stroke risk. Some research has shown that the rate of high blood pressure among blacks in the United States is among the highest in the world, and the prevalence of diabetes in black Americans is nearly twice that of whites. The goal of this study of the REGARDS data was to see what role these traditional risk factors play in stroke disparity.

“Between the ages of 45 and 65, African Americans have a stroke mortality (death rate) about 2 to 3 times higher than whites,” says Dr. Howard. But is the increased risk because they are more likely to die after a stroke or because they’re having more strokes? Data “strongly suggests” the latter, he says, and “this raises the question of why African Americans are having more stroke events.”

One commonly held theory says blacks have more strokes because they have “more of the most important risk factors,” such as high blood pressure and diabetes, Dr. Howard says. The study did find “huge” differences in those two factors:

  • High blood pressure: Whites 51%, Blacks 71%
  • Diabetes: Whites 15%, Blacks 29%

How many strokes were caused by those two risk factors? Not many other studies can solve that puzzle, but that’s exactly the type of question REGARDS was designed to answer, Dr. Howard says. The goal of this study was to explicitly ask (and answer) the question, “How much of the extra risk of stroke in African Americans is simply because they have more high blood pressure and diabetes?”

Stroke incidence

REGARDS study participants’ stroke risk factors, including high blood pressure and diabetes, were measured at the start of the study and their health history was followed to track stroke, so the needed data was available to follow 25,714 patients (of the original 30,239 participants) for 4.4 years. Of the 427 stroke events in that period, each group had approximately 83% ischemic strokes, 13% hemorrhagic strokes, and 5% nonspecific strokes.

Stroke causes

Next they took a closer look at what caused the strokes. The study reports “half of the racial disparity in stroke risk is attributable to traditional risk factors.” And of the half (attributable to traditional risk factors), Dr. Howard says that high blood pressure accounted for about half and diabetes about one-fourth. “The rest was attributable to atrial fibrillation, heart disease, and smoking,” he adds.

What this means for Americans is “if we want to reduce the black-white differences in stroke, then we need to reduce the black-white differences in how many people have high blood pressure and diabetes,” Dr. Howard says. Providing better care for people who already have high blood pressure and diabetes is a nice idea, and important, but that won’t solve the problem.

Instead, he says, “we need to go ‘upstream’ to solve this part of the problem” and stop high blood pressure and diabetes in blacks. As the study noted, “An effort to reduce disparities through these risk factors implies the prevention of the conditions. This potentially could be achieved through interventions on obesity or physical activity or other factors in the pathways of prevention. However, it is not clear whether there are other pathways leading to disparities in the development of these risk factors, a possibility that requires further research.”

The unexplained

And what about the unexplained half of stroke risk — the strokes that were not caused by traditional risk factors? “We think it could be a wide range of things,” Dr. Howard says.

  • Risk factors may have a bigger impact on blacks than whites so factors such as high blood pressure may be more harmful in blacks. “We are investigating this,” he adds. “It looks like this could really be happening.”
  • We may need more precise ways to measure risk factors such as by asking not just whether a patient has high blood pressure but how long he has had it to bring out details that could explain the difference.
  • The answer may lie in “non-traditional” risk factors, such as infections, discrimination or other things that aren’t normally measured, such as sleep apnea, elevated body mass index (BMI is a measure of body fat), physical inactivity, C-reactive protein, coagulation factors, stress, and depression.

Each of these is under investigation, adds Dr. Howard. “The REGARDS study is actively and aggressively trying to figure out if they could be playing a role.”

“We are excited to be making progress” with the help of “the real heroes,” the study participants, Dr. Howard says. The mystery of why more blacks than whites die from stroke has been around more than 50 years he says, but now “we think that we are solving” it.

Mellanie’s Comments — The Afib Connection

So what does this study have to do with afib, and why are we talking about it on an afib site, especially since only a small percentage of strokes in the study were due to afib? Below are a number of related things to consider in conjunction with the results above.

There is a real conundrum, which we discussed previously in our video interview with Dr. Keith Ferdinand, about why blacks have more risk factors for afib (and stroke), but yet seem to have less afib. There are a lot of mysteries yet to be solved, and the REGARDS study will unlock some of those mysteries.

We also know that many folks, regardless of race, aren’t diagnosed with afib until after having a stroke, or two. At the beginning of the REGARDS study, tests were done in each participant’s home, including an ECG (electrocardiogram). Subsequently, participants were contacted every six months by phone. Since ECGs and doctors may fail to find afib that comes and goes (called paroxysmal atrial fibrillation), some in the study may have had undiagnosed afib as a cause of their strokes. We do know from recent research studies that 20%-40% of cryptogenic strokes (strokes of unknown origin) are subsequently found to have been afib strokes. So we need to be more and more rigorous in raising awareness so that those with afib get diagnosed in a timely manner.

Certainly those in the study who had afib and a high CHADS2 score were at increased risk of a stroke. (CHADS2 was created to predict stroke risk in those with atrial fibrillation.) However, two recent studies have shown that you don’t have to have afib for your CHADS2 score to matter. It is in fact also a powerful predictor of stroke risk in those with heart disease who do not have atrial fibrillation. (For more information, see these two studies on CHADS2 and acute coronary syndromes or coronary heart disease.)

In practical terms, what that research means to those with afib is that since most of us also have underlying heart disease, we are still at much greater risk of a stroke if we have any CHADS2 risk factors (such as high blood pressure or diabetes), even if we no longer have afib due to a successful procedure, or even if we are rarely in afib.

A really interesting suggestion from these two studies is that stroke prevention treatments, such as anticoagulants, as well as screening for silent AF among those with heart disease and high CHADS2 scores, may be prudent treatment strategies. Thus it may be worthwhile to discuss with your doctor whether pre-emptive medication is worth considering.

Of course, for those who do not have these conditions, managing lifestyle factors, such as avoiding obesity and staying physically active, may help to prevent them.

Finally, infection and inflammation are starting to be recognized as newer risk factors for heart disease, stroke, and afib, and have garnered lots of research attention lately, so the hypothesis by the researchers of infection being a cause is perhaps highly likely. But could that realistically be more prevalent in blacks than whites?

Because the southern tier of states is known as the “Stroke Belt”, which was intentionally “oversampled” in this study, this could be likely. Having grown up in the south (Birmingham, where much of the REGARDS research team is based), I know that molds, and the recurrent sinus infections due to molds, are a frequent problem in the south due to the high humidity levels. Thus one possibility (this is just my hypothesis, with no research to bear it out) is that low-grade inflammation inhabiting the body over many years due to such infections might not be as readily recognized or dealt with among blacks in the south, which could contribute to their increased susceptibility to stroke.

I believe that the information from these studies has significant value for those in the afib community, and for their family members. The links below will provide more information about topics raised in this article. Please take this seriously so that we can continue to make progress in eliminating strokes.

To learn more, see:

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Last Modified February 29, 2012

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