Burden of hypertension in Black individuals

INTRODUCTION — Hypertension in Black patients as compared with White patients tends to be more common, to present earlier in life, and to be more severe [1,2]. In addition, progression from elevated blood pressure to hypertension is accelerated in Black patients [3]. The reasons for these observations are incompletely understood as the relative importance of environmental and genetic factors has not been established [4,5].

The burden of hypertension in Black individuals is presented in this topic. The treatment of hypertension is discussed separately. (See "Choice of drug therapy in primary (essential) hypertension" and "Goal blood pressure in adults with hypertension".)

HYPERTENSION PREVALENCE AND CONTROL

Prevalence disparity — Hypertension is more prevalent in Black adults as compared with White adults [6,7]. Between 2017 and 2018 in the United States, for example, hypertension (defined as a systolic pressure ≥130 mmHg, diastolic pressure ≥80 mmHg, or use of antihypertensive drug therapy) was present in 57 percent of Black adults compared with 44 percent of White adults [6].

Important risk factors for hypertension among Black patients are largely related to adverse social determinants of health, including lower socioeconomic and educational status, concentrated poverty including lack of access to affordable and high-quality fresh food, and less healthy dietary patterns (eg, ingestion of a high-sodium/low-potassium diet) [8]. The potential importance of social determinants in the disproportionately high prevalence of hypertension among Black adults is reinforced by evidence that prevalent hypertension is comparable among Black and White adults in Cuba [9]. Moreover, African-origin populations with lower social strata in multiracial societies, such as the United States and South Africa, experience more hypertension than would be anticipated based upon anthropometric and measurable socioeconomic risk factors [10].

Another possible mechanism, which is also related to lower socioeconomic status, is poor maternal nutrition leading to low birth weight in the infant. Low birth weight has been associated with an increased risk of hypertension in adulthood, perhaps due in part to impaired kidney growth and development, with fewer functioning nephrons. Although low birth weight is more common in Black infants of mothers who are long-term residents of the United States, birth weights are not lower in Black infants born to mothers who are recent immigrants [11]. In addition, Black immigrants to the United States live eight to nine years longer than Black Americans who were born and are living in the United States [12]. These two observations raise the possibility that the social determinants play a key role, throughout the life course, in the excess prevalence of low birth weight, hypertension, and premature mortality among Black individuals. Low birth weight and adverse social determinants may also contribute to the greater predisposition among Black Americans to end-stage kidney disease (ESKD) [13]. (See "Possible role of low birth weight in the pathogenesis of primary (essential) hypertension".)

Control disparity — In addition to the higher prevalence of hypertension, rates of hypertension control are lower among Black individuals [14-17]. As an example, in a nationally representative sample from the United States, hypertension control rates were 21 percent among Black adults and 24 percent among White adults [14]. The discrepancy in hypertension control was more pronounced comparing Black males with White males (18 versus 24 percent). Control rates are also lower among Black adults in Europe [16,17].

Differences in control rates are likely due, at least in part, to social determinants of health (figure 1). As an example, in a cohort of more than 14,000 Black and White adults who were treated for hypertension, the rate of control (defined as a blood pressure <140/90 mmHg) was lower among Black individuals (64 versus 75 percent) [18]. Compared with White adults, Black adults had lower annual household incomes, lower education levels, were less likely to have health insurance, and resided in more economically disadvantaged neighborhoods and in regions with a shortage of health professionals. In adjusted analyses, differences in these social determinants accounted for one-third of the racial disparity in hypertension control.

RISK OF HYPERTENSIVE COMPLICATIONS

Disproportionately higher burden of complications in Black individuals — Black patients with primary hypertension (formerly called "essential" hypertension) are at much greater risk of developing cardiovascular complications than other demographic groups. This is manifested, in comparison with White patients, by a threefold increase in overall cardiovascular mortality and a six- to sevenfold increase in mortality under the age of 50 years. Black patients are at significantly greater risk for stroke than White patients, especially at younger ages, due in part to the earlier onset and greater severity of hypertension. In addition, the risk of stroke at similar levels of blood pressure may be greater in Black adults than in White adults. In one study, for example, every 10 mmHg higher systolic blood pressure increased stroke risk by 24 percent in Black patients compared with 8 percent in White patients; this disparity in risk extended to individuals whose systolic blood pressure was as low as 120 mmHg [19]. Treatment of hypertension reduces but does not eliminate the racial difference in stroke [20].

In addition to stroke, heart failure is more common among Black individuals. As an example, in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, Black adults had a 23 percent higher relative risk of heart failure hospitalization compared with White adults [21]; social determinants of heath that were more prevalent in Black individuals and that were also associated with heart failure hospitalization included low educational attainment, low annual household income, living in an area with a high poverty rate, poor public health infrastructure, and lack of health insurance.

Black patients also experience earlier development of hypertensive nephrosclerosis, as well as a substantially higher incidence of end-stage kidney disease (ESKD), than White patients, which is most prominent in the 25- to 45-year age group [22-24]. Black patients are also at increased risk for some other kidney diseases, particularly diabetic nephropathy. (See "Diabetic kidney disease: Pathogenesis and epidemiology".)

Reasons for higher complication burden — The higher risk of hypertensive complications in Black individuals is likely due to more severe and poorly controlled hypertension, as well as the social determinants of health (eg, lower socioeconomic status, neighborhood deprivation, lower attained education, other lifestyle factors including lower diet quality), which themselves may account for greater severity of hypertension [25] and may lead to accelerated biological aging [26,27]. There may also be a genetic component, particularly with respect to the higher risk of kidney disease [28-30].

More severe hypertension — The race-related difference in cardiovascular events can be largely mitigated by adequate antihypertensive therapy, suggesting an important role for more severe and less well-controlled hypertension in Black patients [31,32].

In addition, nocturnal hypertension is more common in Black patients, thereby increasing the total daily blood pressure burden [33]. One study evaluated 62 Black and 72 White treated patients with hypertension who were matched for the same daytime blood pressure by ambulatory monitoring [34]. The mean blood pressure between 1 AM and 5 AM was 7 mmHg higher in the Black patients. Why this occurs is not known, but environmental causes are more likely than genetic causes [35,36].

Inadequate antihypertensive therapy — Inadequate antihypertensive therapy may result from therapeutic inertia and medication nonadherence:

●Therapeutic inertia – Clinicians often fail to prescribe adequate pharmacotherapy to control hypertension (ie, therapeutic inertia); therapeutic inertia has a greater adverse impact on populations with a higher prevalence and greater severity of hypertension. In the United States, the average interval between office visits for uncontrolled hypertension is 14 weeks, and intensification of antihypertensive therapy occurs in approximately one out of seven visits [37]. This roughly translates into a required period of two years to adequately control blood pressure in patients with poor control.

It is unclear whether or not therapeutic inertia occurs more frequently in the care of Black patients; some but not all studies identified racial differences [38-40]. One study, for example, followed more than 16,000 patients with uncontrolled hypertension for approximately two years and assessed rates of antihypertensive treatment intensification and the attainment of goal blood pressure [38]. In Black patients, treatment was intensified during approximately 25 percent of clinic visits in which blood pressure was elevated; in White patients, by contrast, treatment intensification occurred in approximately 33 percent of visits in which blood pressure was elevated. At the end of follow-up, fewer Black patients attained goal blood pressure as compared with White patients (66 versus 72 percent).

However, when individuals with hypertension are followed frequently and effective medications, including chlorthalidone, are added and intensified promptly for uncontrolled blood pressure values, blood pressure control and clinical benefits are similar in Black individuals and White individuals. As an example, in the Systolic Blood Pressure Intervention Trial (SPRINT), attained blood pressures were similar among Black and White participants in both the standard and intensive treatment arms [41,42].

●Medication nonadherence – Poor hypertension control may be related in part to antihypertensive medication nonadherence; medication nonadherence is more common in Black individuals and may be related to factors such as lower socioeconomic status, lack of health insurance, distrust in the medical system, greater reliance on alternative therapies [43], less frequent shared decision-making about treatment options [44], and lack of social support networks [25].

Social and environmental factors — Socioeconomic and environmental factors are likely of paramount importance in explaining the disproportionately higher risk of uncontrolled hypertension and of hypertensive complications among Black individuals [8,45-48]. Among a cohort of Black and White American women, for example, lower levels of education, unemployment, lower income, and higher daily stress were all associated with cardiovascular risk, and all were more common in Black American women [46].

Social disadvantages can lead to adverse lifestyle conditions associated with hypertension, such as an unhealthy diet and lack of regular exercise. As an example, Black Americans more frequently ingest a high-sodium/low-potassium diet [47,48], a combination that can both raise the blood pressure and increase the risk of cardiovascular complications. The incidence of salt sensitivity appears to be higher in Black patients than in White patients due perhaps to upward resetting of the set point for tubuloglomerular feedback [49,50]. Black individuals on average have lower values for plasma renin activity than White individuals, which has been associated with salt sensitivity of blood pressure [51]. Of note, potassium supplementation can eliminate racial differences in plasma renin activity and salt sensitivity [52]. (See "Salt intake and hypertension" and "Potassium and hypertension".)

Possible genetic factors — Despite similar degrees of blood pressure control, Black patients appear to remain at higher risk for certain cardiovascular complications of hypertension compared with White patients, including left ventricular hypertrophy and hypertensive kidney disease. In addition, as noted above, blood pressure control does not eliminate racial differences in stroke risk.

As an example, at the same level of blood pressure and total vascular resistance, both left ventricular mass index and renal vascular resistance are higher in hypertensive Black patients than in hypertensive White patients [53]. Furthermore, there appears to be as much as a four- to fivefold increase in the incidence of hypertensive kidney failure in Black patients that persists after the severity of hypertension, degree of hypertensive control, and socioeconomic status are taken into account [54]. Even seemingly adequate control of the hypertension may not be completely protective, as the kidney disease may continue to progress [22,55]. The increase in the incidence of ESKD among older Black patients contrasts with the declining rates of cardiovascular disease that correspond to the overall increase in treatment of hypertension [56].

It has been hypothesized that genetic differences may explain these observations. As an example, polymorphisms in the genes that encode apolipoprotein L1 (APOL1) [28-30] are found far more commonly in Black individuals compared with other populations. These genetic variations appear to confer a markedly increased risk for nondiabetic ESKD, including that due to hypertensive nephrosclerosis and focal segmental glomerulosclerosis (FSGS) [28,29], as well as human immunodeficiency virus (HIV)-associated nephropathy [57]. The APOL1 variant may have had a survival advantage in Africa due to enhanced defense against sleeping sickness [29]. (See "Focal segmental glomerulosclerosis: Clinical features and diagnosis" and "HIV-associated nephropathy (HIVAN)".)

However, there are some data that these racial differences in left ventricular mass, kidney function, and cardiovascular risk, despite similar blood pressure control, are not genetic in origin. In SPRINT, for example, 2466 self-described Black hypertensive patients underwent genotyping, and their degree of West African ancestry (which ranged from 30 to 100 percent) was determined using previously established ancestry-informative genetic markers [58]. Achievement of blood pressure targets was not affected by ancestry. During more than three years of follow-up, changes in left ventricular mass and kidney function were similar across individuals with different degrees of West African ancestry. In addition, those with the highest degree of West African ancestry had a lower risk of cardiovascular events.

GOAL BLOOD PRESSURE — In summary, effective antihypertensive therapy is particularly important in Black patients. A discussion of which antihypertensive drugs should be used can be found elsewhere. (See "Choice of drug therapy in primary (essential) hypertension".)

The optimal blood pressure in Black patients is similar to that in other patients and depends in part upon comorbid conditions and overall cardiovascular risk. These issues are discussed in detail elsewhere. (See "Goal blood pressure in adults with hypertension".)

The two largest studies to examine goal blood pressure in Black patients were the Systolic Blood Pressure Intervention Trial (SPRINT) and the African American Study of Kidney Disease and Hypertension (AASK). SPRINT enrolled individuals at high cardiovascular risk, whereas AASK enrolled patients with hypertensive nephrosclerosis:

●SPRINT, discussed in detail elsewhere, assigned 9361 patients, including 2802 non-Hispanic Black patients, to a systolic blood pressure goal of <120 mmHg or a goal of <140 mmHg [59]. The benefit from more intensive blood pressure lowering was similar in Black and other racial subgroups. (See "Goal blood pressure in adults with hypertension", section on 'Patients with established atherosclerotic cardiovascular disease'.)

●AASK included 1094 African Americans with long-standing hypertension, otherwise unexplained slowly progressive chronic kidney disease, and mild proteinuria (mean of approximately 500 to 600 mg/day but a median of approximately 100 mg/day) [60]; this pattern in Black patients is almost always associated with histologic changes compatible with nephrosclerosis as the sole disease [61]. The patients were allocated to one of three drugs, ramipril (463 patients), metoprolol (441 patients), or amlodipine (217 patients), and to one of two blood pressure goals, 125/75 or 140/90 mmHg. The effect of the goal blood pressure in AASK is presented separately. (See "Antihypertensive therapy and progression of nondiabetic chronic kidney disease in adults", section on 'AASK trial of goal blood pressure'.)

Recommendations by others — In November 2010, a consensus statement concerning the management of high blood pressure in African Americans was published by the International Society on Hypertension in Black patients [62]. For those with uncomplicated primary hypertension (formerly called "essential" hypertension), a goal blood pressure less than 135/85 mmHg was considered a reasonable target. A lower goal of less than 130/80 mmHg was recommended in patients at increased risk, such as those with atherosclerotic cardiovascular disease, diabetes, or proteinuric chronic kidney disease. However, the 2017 American College of Cardiology/American Heart Association (ACC/AHA) hypertension guidelines recommended a blood pressure target of less than 130/80 mmHg and did not make separate recommendations for Black patients [63].

Our recommendations on goal blood pressure, and the ACC/AHA recommendations, are presented separately. (See "Goal blood pressure in adults with hypertension".)

SUMMARY

●Burden of hypertension – Hypertension develops earlier in life and is more common and more severe in Black as compared with White patients. Black patients are less likely to have controlled blood pressure and are at greater risk of developing hypertensive complications compared with White patients. (See 'Introduction' above and 'Hypertension prevalence and control' above.)

●Reasons for increased burden – The increased risk of uncontrolled hypertension and hypertensive complications is likely due to multiple factors including the increased severity of hypertension, inadequate antihypertensive therapy, social determinants of health (eg, environmental and socioeconomic factors) (figure 1), and possibly genetic factors. (See 'Risk of hypertensive complications' above.)

●Goal blood pressure – The optimal goal blood pressure in Black patients is similar to that in other patients and depends in part upon comorbid conditions and overall cardiovascular risk. Goal blood pressure is discussed separately:

•(See 'Goal blood pressure' above.)

•(See "Goal blood pressure in adults with hypertension".)

•(See "Antihypertensive therapy and progression of nondiabetic chronic kidney disease in adults", section on 'Blood pressure goal'.)

•(See "Treatment of hypertension in patients with diabetes mellitus".)