Hypertension in African Americans

Hypertension Risk Factors

Important risk factors that predispose to hypertension include advancing age, a strong family history of hypertension, obesity, physical inactivity, high dietary sodium intake, low dietary potassium intake, low vitamin D intake, harmful use of alcohol, psychosocial stress, low socioeconomic status, low educational attainment, and psychological traits such as anger and hostility. These factors are as important in African Americans as they are in other race-ethnic population subgroups. However, they take on additional significance when a greater prevalence of any of them in African Americans is used to explain the greater prevalence of hypertension in this population.

Hypertension Incidence

Hypertension incidence is strongly influenced by age, baseline BP level, the definition of hypertension, and duration of follow-up. It is also influenced by sex, race, ethnicity, family history, obesity, geography, and several psychosocial, environmental, and biomedical risks. Although older studies showed a higher incidence of hypertension in African Americans, more recent, carefully controlled studies of longer duration paint a more nuanced picture. For example, in younger adults who were aged 18 to 30 years when recruited in 1985 to 1986 in the community-based Coronary Artery Risk Development in Young Adults (CARDIA) cohort, hypertension incidence after 20 years of follow-up was significantly higher in African Americans, especially women, even after adjustment for age, race, heart rate, body mass index, smoking, family history, education, uric acid, alcohol use, physical activity, and baseline systolic BP. For example, when the mean age was approximately 45 years, the 20-year incidence was 34.5% in black men, 37.6% in black women, 21.4% in white men, and 12.3% in white women; p < 0.001. Hypertension incidence also varied significantly across urban areas and by race and sex, with higher rates in the southeast and in blacks, especially African-American women. In the Trials of Hypertension Prevention, the incidence of hypertension (defined as BP ≥ 160/95 mm Hg or taking antihypertensive medications) over 7 years of follow-up in middle-aged African Americans and whites was nearly identical (25.7% in African Americans and 25.3% in whites). In the Multi-Ethnic Study of Atherosclerosis, participants aged 45 to 84 years at baseline were followed for a median of 4.8 years for incident hypertension, defined as systolic BP 140 or higher mm Hg, diastolic BP 90 or higher mm Hg, or the initiation of antihypertensive medications. After adjustment for age, sex, and study site, hypertension incidence was higher for African Americans aged 45 to 64 compared with whites but not for those 75 to 84 years of age.

Hypertension Prevalence

Most published studies demonstrate that hypertension prevalence is significantly greater in African Americans compared with other race-ethnic groups in the United States. As shown in Fig. 41.1 , the age-adjusted prevalence in the most recent National Health and Nutrition Examination Survey (2011–2014) was higher in non-Hispanic African-African women (41.5%) and men (40.8%) compared with all other race-ethnic-sex groups. Importantly, in both non-Hispanic African-African women and men, the age-adjusted prevalence has steadily increased in graded fashion over all three national surveys in 1988 to 1994, 1999 to 2006, and 2007 to 2012. Fig. 41.2 shows the extent of the increase in hypertension prevalence in U.S. counties from 2001 to 2009 and the particularly marked increase seen in African-African men and women.

Hypertension Severity

In addition to their greater prevalence of hypertension, African Americans (in comparisons with whites) develop hypertension at an earlier age ; have higher average BP levels; and higher average nondipping nocturnal BP and greater 24-hour BP variability on ambulatory monitoring. Additionally, African Americans are more likely to experience accelerated conversion from prehypertension to hypertension. As a result, severe hypertension is more common in African Americans compared with whites and is often more likely to be associated with a greater prevalence of target organ damage. However, there is little, if any, evidence that hypertension is a different disease or is “more severe” in African Americans. Thus race, per se, does not cause more severe hypertension. As Schmieder et al. demonstrated in a matched-pair analysis of early target organ damage that also controlled for confounding factors such as age, sex, body weight, and BP level, race per se does not predict hypertension severity or extent of target organ damage.

Awareness, Treatment, and Control

Over the last three decades, awareness and treatment of hypertension in African Americans have improved significantly as it has in the general population ( Fig. 41.3 ). In fact, hypertension awareness has been higher in non-Hispanic blacks compared with the total U.S. population or in non-Hispanic whites and Hispanics in most years of the survey ( Fig. 41.3 ). In 2011 to 2012, hypertension treatment rates were similar among non-Hispanic blacks (76.5%), and non-Hispanic whites (75.8%) but lower in Mexican Americans (69.6%).

Although hypertension control has also improved steadily over the last three decades, the most recent control rate in African Americans (49.4%) is lower than that in non-Hispanic whites (54.3%) and also lower than achievable in an integrated health system model that uses implementation, dissemination, and performance feedback strategies in chronic disease care. For example, the Kaiser Permanente Southern California health care system was able to improve hypertension control in a multiethnic population from 54% to 86% in the total population and achieved a control rate of 80% or more in African Americans and other population subgroups, regardless of preferred language or type of health insurance plan.

Mortality and Morbidity

The age-adjusted hypertension-related mortality rate in non-Hispanic blacks is nearly double the rate seen in non-Hispanic whites and Hispanics ( Fig. 41.4 ). The disparity is even starker when examined by sex. For example, in 2013, the death rates per 100,000 population were 51.6 for non-Hispanic black males but 18.9 for non-Hispanic white males, and 20.0 for Hispanic males. The corresponding rates for women were 36.5 for non-Hispanic black females, 15.8 for non-Hispanic white females, and 15.3 for Hispanic females. Hypertension is also an important contributor to stroke, myocardial infarction (MI), heart failure, kidney failure, and other morbid events and reduced quality of life in African Americans. The greater prevalence of hypertension, onset at an earlier age, and lower control rates in African Americans, compared with whites, contribute to the greater prevalence of hypertensive target organ damage in the heart, brain, kidney, and arterial vasculature with resulting chronic organ failure and reduced quality of life.