Hypertension a 'Triple Curse' for African Americans

Some researchers call hypertension a "triple curse" for African Americans, especially those aged 45 to 65 years.

It's well known that the prevalence of hypertension is much higher among blacks than whites. And recent research showed that African Americans are more likely than whites to be aware of having hypertension and to be treated for it, but less likely to have it controlled.

Now, a new study has found that a 10–mm Hg increase in blood pressure is associated with a 3 times greater increase in stroke risk among blacks compared with whites.

"African Americans are more likely to be hypertensive, and once they're hypertensive, they're less likely to have their blood pressure controlled; and once it's not controlled, it's 3 times worse" in terms of stroke risk, said lead author George Howard, DrPH, professor, biostatistics, School of Public Health, University of Alabama at Birmingham. Together, this amounts to what he referred to as a "triple curse."

"I'm not saying that it's not important for white people to get their blood pressure under control; it is," said Dr. Howard. "I'm saying that it is much more important for blacks."

The study was published online December 10 in Archives of Internal Medicine.

Longitudinal Study

The analysis used data from 27,748 participants in the Reasons for Geographic And Racial Disparities (REGARDS) study, a population-based longitudinal cohort study of black and white people aged 45 years and older who were recruited between 2003 and 2007 and followed to 2011.

Researchers assessed stroke risks factors through phone interviews and physical examinations, which included collection of blood pressure levels. They stratified participants by age (45 to 65 years, 65 to 74 years, and 75 years and older) and classified participants as normotensive (systolic blood pressure [SBP] less than 120 mm Hg), prehypertensive (120 to 139 mm Hg), or stage 1 hypertensive (140 to 159 mm Hg).

Because only 1.6% of whites aged 45 to 64 years had stage 2 hypertension stage (SBP 160 mm Hg or greater), this category was omitted from the analyses.

Except for smoking, older participants and those with higher blood pressure generally had more risk factors. Across age and SBP levels, black participants were more likely to be using antihypertensive medications and to have a higher prevalence of diabetes and left ventricular hypertrophy, but less likely to have atrial fibrillation and heart disease.

The investigators found that more blacks than whites had hypertension (71% versus 51%). "That's a huge difference," Dr. Howard stressed.

During 4.5 years of follow-up, 715 incident strokes occurred. Overall, there was a 14% increased risk for stroke associated with a 10–mm Hg higher SBP (hazard ratio [HR], 1.14; 95% confidence interval [CI], 1.08 - 1.21).

However, there was evidence of racial differences in this association ( P for interaction = .02) with an 8% increase in whites (HR, 1.08; 95% CI, 1.00 - 1.16) and a 24% increase in blacks (HR, 1.24; 95% CI, 1.14 - 1.35).

Adjustment for risk factors reduced the estimated effect of SBP differences, but the same pattern of racial differences persisted ( P for interaction = .049).

Striking Disparity

The racial disparity in stroke risk was particularly striking in persons aged 45 to 64 years. Here, the black-to-white HR was 0.87 (95% CI, 0.48 - 1.57) for normotensive participants, 1.38 (95% CI, 0.94 - 2.02) for those with prehypertension, and 2.38 (95% CI, 1.19 - 4.72) for those with stage 1 hypertension.

A similar pattern of increasing disparity in stroke was seen for those aged 65 to 74 years, but the differences were not as dramatic. The smaller black-to-white HRs at older ages is perhaps not surprising because the overall magnitude of black-white racial disparities in the age strata is substantially smaller, said the authors.

(Research shows that the risk for death from stroke among blacks younger than 65 years is 2 to 3 times higher than that among whites of the same age, but the racial disparity decreases with age and is completely absent by age 85 years.)

Dr. Howard said he would love to see a study that included both blacks and whites aged 40 to 60 years who were randomly assigned to "ordinary" blood pressure control (in which physicians try to reduce blood pressure to 120 to 140 mm Hg) or to aggressive blood pressure therapy (in which they seek a decrease to 120 mm Hg).

Such a trial might help determine whether the benefits of aggressive therapy are worth the risks of having patients take several medications. In some cases, adequate blood pressure control requires 5 or 6 medications, all of which might have adverse effects, said Dr. Howard.

"The question is, is the benefit from aggressive blood pressure therapy more than offset by the number of medications that it would take to be that aggressive, and would that eliminate the huge racial disparity in stroke risk?"

In this study, much of the excess stroke risk in those aged 45 to 64 years was among patients with stage 1 hypertension. Reducing blood pressure among middle-aged African Americans to below 120 mm Hg may be a "lofty" goal, but the theoretical economic and public health implications are "staggering," said the authors. They speculated that the "ballpark" cost savings could be $3.3 billion a year.

Dr. Howard stressed that controlling blood pressure among African Americans is the responsibility of physicians as well as patients. As it stands, blacks appear to seek treatment for hypertension but fail to get it adequately controlled.

"I don't think the blame can be laid on either the physician's doorstep or on the patient's doorstep." Dr. Howard lays much of the blame on a food system that "pumps out" salt.

Invited to comment on this study, Salvador Cruz-Flores, MD, professor and acting chair, Department of Neurology and Psychiatry, Saint Louis University School of Medicine, Missouri, said he found it "very compelling".

The study results suggest that there could be a "biological determinant" at play that makes African Americans more susceptible to the effects of high blood pressure, said Dr. Cruz-Flores.

He pointed out, however, that the findings were based on a single measure of blood pressure taken at the beginning of the study. "We don't know what type of blood pressure control these people had over the years they were followed," said Dr. Cruz-Flores. "The authors are making an assumption, which is probably correct, that blood pressure was sustained at that level for the period of time the subjects were followed, but we don't know whether that's true or not."

Another limitation of the study, he said, is that although the authors adjusted for a number of different stroke risk factors, there may be others that weren't accounted for that could potentially explain the difference in risks between blacks and whites.

He also offered a "word of caution" about expecting stroke risk among young African Americans to equal that of whites if their blood pressure was lowered to below 120 mm Hg. That assumption "should be taken with a grain of salt," he said, given that effect sizes in clinical trials are usually lower than those seen in observational studies.

The study was supported by the National Institute of Neurological Disorders and Stroke. The authors and Dr. Cruz-Flores have disclosed no relevant financial relationships.