Correspondence

Racial Differences in the Outcome of Left Ventricular Dysfunction

N Engl J Med 1999; 341:287-288July 22, 1999

Article

To the Editor:

In their article on racial differences in the outcome of left ventricular dysfunction, Dries et al. (Feb. 25 issue)1 conclude that “black patients with asymptomatic or symptomatic left ventricular systolic dysfunction appear to be at higher risk for progression of heart failure and for death than similarly treated white patients, even when adjustment is made for differences in the severity and cause of heart failure, the management of heart failure, coexisting illnesses, and socioeconomic status.” The authors speculate that physiologic differences, presumably genetically determined, account for the otherwise unexplained differences in outcome.

This conclusion seems unwarranted on several grounds. First, the ability of their statistical model to adjust for all the prognostic factors that affect outcome in patients with congestive heart failure is doubtful. Second, the unexplained differences that remained after the attempts at adjustment may be due to unrecognized environmental or behavioral factors that were not included in the model. Third, the presumed genetic homogeneity of the American black population has been challenged by recent research suggesting that perhaps 80 percent of American blacks have at least one white ancestor. Fourth, the presumed genetic homogeneity of the U.S. white population is untenable, given the diversity of the immigrants who have arrived from four continents.

In sum, racial classifications have been abandoned by many geneticists, physical anthropologists, and evolutionary biologists, and recent findings in studies of DNA and genetic markers in populations add credence to the notion that the division of the human species into so-called races on the basis of skin color is unscientific and unjustified.2 As used in the United States, the term “race” is a social and political construct, and differences in disease prognosis are more likely to be due to behavioral or environmental differences than to physiologic ones associated with skin color.

Paul D. Stolley, M.D., M.P.H.
University of Maryland, Baltimore, MD 21201-1596

2 References

1
Dries DL, Exner DV, Gersh BJ, Cooper HA, Carson PE, Domanski MJ. Racial differences in the outcome of left ventricular dysfunction. N Engl J Med 1999;340:609-616
Full Text | Web of Science | Medline

2
Rose MR. Darwin's spectre: evolutionary biology in the modern world. Princeton, N.J.: Princeton University Press, 1998.

To the Editor:

Dries et al. suggest that differences in the natural history of left ventricular dysfunction between blacks and whites may account for their observation of racial differences in the outcome of this disorder. Their conclusion is based on the supposition that they have accounted for the more obvious explanation of socioeconomic differences between blacks and whites. They point to two features of their study that they believe reduce the likelihood that their observations are attributable to racial differences in socioeconomic status.

First, their data were from a trial in which all subjects received standardized treatment and follow-up. Although this is clearly a strength of the study, it does not provide reassurance that the observed differences are not attributable to socioeconomic status. Previous work has clearly demonstrated that socioeconomic differences in health are minimally attributable to differences in health care.1

Second, the authors adjusted for variables intended to represent socioeconomic status. These adjustments, however, fall far short of accounting for socioeconomic differences between blacks and whites. The two variables used are dichotomous and ignore the fact that in any given category, socioeconomic conditions are typically worse for blacks than for whites.2 Moreover, given the well-established and consistent relation between socioeconomic status and the risk of death, the absence of an association between the presence of “financial distress” and the risk of death in this study suggests that this variable, as measured, is a poor proxy for socioeconomic status. Statistical modeling has shown that when socioeconomic variables are broadly categorized or are poor correlates of socioeconomic status, the likelihood of falsely detecting an “independent” effect of race on outcomes is substantial.2

Obviously, it is impossible to control perfectly for the complex and somewhat nebulous concept of socioeconomic status in any study, and Dries et al. appropriately advise caution in the interpretation of their results. By focusing, however, on biologic factors as the fallback explanation for their findings, the authors pay inadequate attention to the environmental, psychosocial, and economic factors that are just as likely, if not more likely, explanations of racial differences in health.3 Race is at least as much a social construct as a biologic one. More researchers should treat it as such.

Somnath Saha, M.D., M.P.H.
Portland Veterans Affairs Medical Center, Portland, OR 97207

3 References

1
Adler NE, Boyce WT, Chesney MA, Folkman S, Syme SL. Socioeconomic inequalities in health: no easy solution. JAMA 1993;269:3140-3145
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2
Kaufman JS, Cooper RS, McGee DL. Socioeconomic status and health in blacks and whites: the problem of residual confounding and the resiliency of race. Epidemiology 1997;8:621-628
CrossRef | Web of Science | Medline

3
Krieger N, Williams DR, Moss NE. Measuring social class in US public health research: concepts, methodologies, and guidelines. Annu Rev Public Health 1997;18:341-378
CrossRef | Web of Science | Medline

To the Editor:

The concept of race is a fundamentally flawed idea that developed because of social rather than scientific reasons. Most scientific disciplines, such as anthropology, have rejected the concept because there is no biologic or genetic basis for it. For some reason, however, doctors and epidemiologists still insist that differences in race account for outcome. The article by Dries and colleagues continues this flawed tradition. Despite the use of multivariate analysis of retrospective data, they found that blacks had poorer blood-pressure control than whites. By focusing on the differences in skin color, the study camouflages the message that physicians need to control blood pressure aggressively in patients with left ventricular dysfunction, often by restricting salt intake when using angiotensin-converting–enzyme inhibitors.

Sudarshan Hebbar, M.D.
6530 Troost Ave., Kansas City, MO 64131

Author/Editor Response

The authors reply:

To the Editor: Race is a complex issue.1 The intent of our analysis was to illustrate the importance of self-reported race with respect to outcome. Our results are consistent with those of other studies1 and show that there are important differences in outcome among persons in different racial groups. Moreover, the blood-pressure response to angiotensin-converting–enzyme inhibition2 and neuroendocrine activation in heart failure3 differ between black Americans and white Americans, providing a plausible mechanistic explanation for our observations.

As shown in Table 1 of our article, diastolic blood pressure was significantly higher at base line in black participants than in white participants, reflecting a higher prevalence of hypertension among blacks (62 percent vs. 36 percent). However, when data on diastolic blood pressure were stratified according to the history of hypertension, little difference between the groups was observed (Table 1Table 1Diastolic Blood Pressure at Base Line in Blacks and Whites, According to the Presence or Absence of a History of Hypertension.). Hypertension is a recognized risk factor for heart failure,4 but higher base-line values for diastolic blood pressure were associated with a lower risk of death in our analysis. Each increase of 5 mm Hg in diastolic blood pressure was associated with an absolute reduction in the risk of death of 4 to 6 percent (Table 4 and Table 5 of the article).

Systolic blood pressure was similar in the two groups at base line (Table 1 of the article) and not independently associated with the risk of death (relative risk, 1.00 per increase of 5 mm Hg; 95 percent confidence interval, 0.97 to 1.03). Furthermore, when systolic blood pressure was added to the multivariate models, the results were unchanged. Follow-up blood-pressure values may have prognostic importance in patients with heart failure, but they were not evaluated in our analysis. We recognized the importance of base-line diastolic blood pressure and the presence or absence of a history of hypertension and included these variables in the multivariate models.

Regarding our assessment of socioeconomic status, we acknowledge the limitations of any assessment involving surrogate measures, though such approaches are in widespread use. Although the presence or absence of financial distress is less commonly used as a marker of income, there is no reason to think that it is any worse, or better, than other approaches, such as household-income categories or arbitrary “poverty” cutoff points. Residual confounding is of potential concern in any multivariate analysis; however, the consistency between our unadjusted and adjusted results is reassuring.

Although Drs. Stolley, Saha, and Hebbar question the value of our results, we strongly believe they highlight the fact that there are important differences in prognosis between black Americans and white Americans with heart failure. Additional research is required to address the origin of these differences and to develop methods of correcting these imbalances.

Daniel L. Dries, M.D., M.P.H.
Derek V. Exner, M.D., M.P.H.
Michael J. Domanski, M.D.
National Heart, Lung, and Blood Institute, Bethesda, MD 20892-7936

4 References

1
Lillie-Blanton M, Parsons PE, Gayle H, Dievler A. Racial differences in health: not just black and white, but shades of gray. Annu Rev Public Health 1996;17:411-448
CrossRef | Web of Science | Medline

2
Materson BJ, Reda DJ, Cushman WC, et al. Single-drug therapy for hypertension in men -- a comparison of six antihypertensive agents with placebo. N Engl J Med 1993;328:914-921[Erratum, N Engl J Med 1994;330:1689.]
Full Text | Web of Science | Medline

3
Benedict CR, Shelton B, Johnstone DE, et al. Prognostic significance of plasma norepinephrine in patients with asymptomatic left ventricular dysfunction. Circulation 1996;94:690-697
Web of Science | Medline

4
Levy D, Larson MG, Vasan RS, Kannel WB, Ho KK. The progression from hypertension to congestive heart failure. JAMA 1996;275:1557-1562
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