Abstract
Background.
Cardiovascular disease is the main cause of death in older adults. Uncontrolled blood pressure is an important risk factor for cardiovascular disease. African Americans have poorer blood pressure control than non-Hispanic whites. Little is known about whether this difference persists in older ages or the factors that contribute to this racial gap.
Methods.
Data were obtained from participants of the Chicago Health and Aging Program. Blood pressure control was defined according to JNC-7 criteria. Univariate chi-square analyses were used to determine racial differences in hypertension and blood pressure control, whereas sequential multivariate logistic regression models were used to determine the effect of race on blood pressure control.
Results.
African Americans had a higher prevalence of hypertension (74% vs 63%; p < .001), higher awareness of hypertension (81% vs 72%; p < .001), and poorer blood pressure control (45% vs 51%, p < .001) than non-Hispanic whites. Racial differences in blood pressure control persisted after adjustment for socioeconomic status, medical conditions, obesity, and use of antihypertensive medications (odds ratio = 0.84, 95% confidence interval = 0.70–0.94). From 1993 to 2008, blood pressure control improved more among non-Hispanic whites than among African Americans.
Conclusions.
Racial differences in blood pressure control in older adults were not explained by socioeconomic status. The racial disparity in the prevalence and control of hypertension remained consistent for older hypertensive individuals eligible for Medicare. Although the rates of hypertension control improved for both racial groups, the improvement was greater among whites, thus widening the gap in this older population at high risk for cardiovascular disease.
Key Words: Blood pressure control, Elderly, Race, Disparities, Medicare
In the United States, more than 31% of the population has hypertension or is taking antihypertensive medication. The prevalence of hypertension rises to more than 60% in older age and is higher in both middle-aged and older African Americans compared with non-Hispanic whites (1,2).
Although large-scale clinical trials have shown that the control of elevated blood pressure significantly reduces the risk for major cardiovascular disease (CVD) outcomes (3,4), a substantial portion of hypertensive patients do not achieve blood pressure control (1). Data from the 2005–2006 National Health and Examination Survey suggest that blood pressure is controlled for only 64% of all patients on antihypertensive medication. Moreover, the control rate is considerably lower in adults 60 years and older compared with younger adults (58% vs 72%, respectively) (1), which may in part contribute to the 80% of deaths among adults 65 years of age or older that are attributed to CVD (5).
African Americans also tend to have poorer blood pressure control compared with other racial/ethnic groups (1,2). These racial differences have been partially explained by inequalities in health care access (2). However, there is very little information on racial differences in blood pressure control in older populations where more universal access to health care through Medicare might translate into smaller racial gaps in blood pressure control. Although a handful of studies suggest that racial differences in blood pressure control persist into older age (6), there is little information about the different factors that account for the differences in blood pressure control among older African American and white adults.
Our goal in this analysis was to use data from a large population-based epidemiological study of African Americans and whites to examine the magnitude of racial differences in blood pressure control among older adults who report having and being treated for high blood pressure. In addition, we evaluated the role of socioeconomic status (SES), comorbid conditions, obesity, and use of antihypertensive medications as contributors to racial differences in blood pressure control.
METHODS
Study Design and Population
Data come from the Chicago Health and Aging Program (CHAP), an ongoing population-based study of Alzheimer’s disease and other common chronic conditions of older age. CHAP has been previously described in detail (7). Briefly, between 1993 and 1996 the CHAP study conducted a census of the entire population of three community areas on the south side of Chicago. These communities were selected because they contained a roughly equal number of African Americans and non-Hispanic whites, with a reasonably wide spectrum of SES within each group, and a residentially stable population conducive to the conduct of a longitudinal study. All residents aged 65 years and older were identified in the census and were invited to participate. Of the 7,813 eligible residents, 6,158 (78.9%) enrolled. The baseline assessment took place from 1993 to 1996 and consisted of an in-person interview conducted in the participants’ homes. The assessment included structured questions on sociodemographic variables, medical history, and various other domains as well as a standardized assessment of blood pressure and other biological measures. Assessments have been repeated in 3-year cycles until the present. To maintain a stable cohort size, new age-eligible participants were added to the original cohort starting in 2000 and participated in the same 3-year cycles of interviews. As of 2003, residents aged 65 years and older from an adjacent community area were also invited to participate, to provide a more racially balanced study population. The present analysis combines the baseline data from the original cohort and successive age cohorts, which were collected during the following periods: 1993–1996, 2000–2002, 2003–2005, and 2006–2009. Our analysis is restricted to participants who self-identified as African American or non-Hispanic white (N = 9,406). Less than 1% of all participants were excluded due to being of another racial or ethnic group. The CHAP study is approved by the Institutional Review Board at Rush University Medical Center.
Study Measures
Blood pressure measures.—
The interview included assessment of actual blood pressure according to the Hypertension Detection and Follow-Up Program protocol (8). Mercury sphygmomanometers were used from 1993 to 2005; these were replaced with digital sphygmomanometers starting in 2006. Arm blood pressure was measured twice, 1 minute apart, in the seated position in the nondominant arm following a 5-minute rest using a random sphygmomanometer. The average of the two values was used as measures of systolic and diastolic blood pressure, respectively. High blood pressure was defined according to the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure criteria (JNC 7) (9) as having a systolic blood pressure ≥ 140 mmHg or a diastolic blood pressure ≥ 90 mmHg upon examination, or self-reported current use of medication for high blood pressure.
Definition of hypertension awareness, treatment, and control.—
A person was considered “aware” of hypertension if he/she answered positively to the question “Have you ever been told by a doctor, nurse, or therapist that you have high blood pressure?” A participant was considered “treated” if he/she reported taking antihypertensive medications at the time of the interview or if the interviewer corroborated the use of medications with antihypertensive properties upon review of the participant’s medications. A treated participant was considered to have his/her blood pressure “controlled” if his/her average systolic blood pressure was less than 140 mmHg and his/her average diastolic blood pressure was less than 90 mmHg according to JNC-7 criteria. This approach is consistent with previous studies of blood pressure control (1,10,11). Due to the lack of diagnostic evaluations in CHAP, we did not use stricter blood pressure control guidelines for specific patient subpopulations (ie, patients with diabetes).
Medication variables.—
As part of the interview, participants were asked to show all prescription and over-the-counter medications to the interviewer, who recorded name and dosage. Medications were then classified using the MediSpan system (12), which facilitates grouping them by their biological active agents, including individual ingredients of combination products. We created a separate variable by grouping all medications that may have antihypertensive effects, including diuretics, beta-blockers, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers, and central acting antihypertensives. For convenience, we will refer to these medications as antihypertensive medications, while acknowledging we did not collect information on the specific medical condition for which each medication was prescribed.
Demographic and other measures.—
Demographic measures included participant age, race, income, and educational attainment. Age at the time of interview was calculated using self-reported date of birth. Questions on race were based on the U.S. Census questionnaires. Total household income was measured at the time of the interview using a color-coded card with 10 income categories, ranging from less than $5,000/yr to more than $75,000/yr. Educational attainment was recorded as years of formal schooling completed.
Body mass index was calculated based on participants’ height and weight. Weight was measured at the time of the interview using a digital scale on a hard flat surface without shoes and was recorded in pounds. Height was reported by participants in feet and inches. Body mass index (kg/m2) was computed by converting height and weight to metric figures. Obesity status was determined for every participant with a body mass index calculated value equal to or greater than 30. Information on concurrent chronic medical conditions was obtained at the time of interview. Interviewers asked participants to self-report a history of other medical conditions diagnosed by a health care provider. These diagnoses included cancer, myocardial infarction, diabetes, hip fracture, and stroke.
Analysis
In order to focus on racial differences in blood pressure control, analysis was limited to participants treated for hypertension.
Univariate chi-square analysis was used to evaluate differences between African American and non-Hispanic white participants in demographic, social, and medical characteristics. A multiple imputation procedure was performed to account for missing income data in 12% of participants.
To evaluate racial differences in blood pressure control, we conducted sequential multivariate logistic regression models: The first model tested the relationship between race and blood pressure control after adjusting for age and sex. In the second model, we added education and income to evaluate how these variables modified the relationship between race and blood pressure control. In the subsequent models, terms for comorbid conditions, obesity, and the observed use of antihypertensive medications were included to determine their role in racial differences in blood pressure control. In secondary analyses, we added interaction terms of race with age, sex, income, and education to see if racial differences in blood pressure control varied as a function of these characteristics. Finally, in an exploratory analysis, we assessed temporal trends in racial differences in blood pressure control. To that end, we added terms for the time of interview to the logistic regression model and the interaction between cycle of interview and race. Statistical analyses were conducted using the SAS analytical software (Raleigh, NC).
RESULTS
Of the 9,406 CHAP participants, 6,608 (70%) were found to have high blood pressure at their baseline interview. Of these, 5,178 (78%) indicated that they were aware of their high blood pressure, and of these, 4,850 (92%) reported being treated for high blood pressure (Table 1). In general, compared with non-Hispanic whites, African Americans had a higher prevalence of high blood pressure (74% vs 63%; p < .001), were more likely to be aware of it (81% vs 72%; p < .001), and to report being currently treated for it (94% vs 92%; p = .003).
Table 1.
Hypertension by Race*
| N | Hypertension Prevalence | Hypertension Awareness | Reported Treatment | Hypertension Control | |
| Total | 9,406 | 6,608 (70%) | 5,178 (78%) | 4,850 (92%) | 2,288 (47%) |
| African American | 6,019 | 4,469 (74%) | 3,628 (81%) | 3,379 (94%) | 1,536 (45%) |
| Non-Hispanic white | 3,387 | 2,139 (63%) | 1,550 (72%) | 1,471 (92%) | 752 (51%) |
| p Value | <.001 | <.001 | <.05 | <.001 |
*Percentages were calculated using the number in the immediate left column as the denominator.
Demographic Characteristics
The remainder of the analysis focuses on participants treated for hypertension (Table 1, column 3; n = 4,850). Their demographic characteristics are presented in Table 2. Participants were predominantly African American and female. African Americans tended to be younger, had fewer years of education, and lower income than non-Hispanic whites. Obesity was more prevalent in African Americans. Although there was no difference in the mean number of medical conditions between both groups, the number of participants with cancer, diabetes, stroke, and hip fracture was significantly different between the two racial groups (Table 2).
Table 2.
Demographic Characteristics of the Study Sample for Participants Treated for Hypertension.
| Overall Sample (n = 4,850) | African Americans (n = 3,379) | Non-Hispanic Whites (n = 1,471) | p Value | |
| Demographic characteristics | ||||
| Age, mean (SD) | 72.4 (6.3) | 71.2 (5.5) | 75.2 (7.1) | <.001 |
| Female, % | 63 | 64 | 61 | <.05 |
| Years of education, mean (SD) | 12.1 (3.3) | 11.5 (3.3) | 13.6 (3.1) | <.001 |
| Income (US$) | <.001 | |||
| Less than 15,000, % | 38 | 38 | 23 | |
| 15,000–30,000, % | 38 | 42 | 28 | |
| More than 30,000, % | 27 | 20 | 49 | |
| Obesity, % | 37 | 41 | 28 | <.001 |
| At least one other medical condition, %* | 46 | 45 | 48 | <.05 |
| Medical conditions | ||||
| Myocardial infarction, % | 17 | 16 | 18 | .35 |
| Cancer, % | 19 | 16 | 25 | <.001 |
| Stroke, % | 12 | 13 | 11 | <.05 |
| Diabetes, % | 10 | 13 | 5 | <0.001 |
| Hip fracture, % | 3 | 2 | 4 | <.001 |
| Blood pressure-related variables | ||||
| Number of antihypertensives, mean (SD) | 1.6 (0.8) | 1.6 (0.8) | 1.5 (0.8) | .10 |
| Antihypertensive class | ||||
| ACE inhibitors, % | 34 | 33 | 35 | .26 |
| Beta blockers, % | 28 | 24 | 36 | <.001 |
| Calcium channel blockers, % | 40 | 43 | 32 | <.001 |
| Diuretics, % | 46 | 49 | 39 | <.001 |
| Other, % | 9 | 9 | 10 | .25 |
*Medical conditions other than hypertension.
Blood pressure–related variables.—
Blood pressure was controlled in less than half (47%) of the participants with reported treatment for hypertension, with a significantly lower control rate among African Americans than non-Hispanic whites (45% vs 51%; p < .001) (Table 1). No racial differences were observed in the number of antihypertensive medications prescribed to participants (Table 2). Prescriptions for calcium channel blockers and diuretics were proportionally higher among African Americans, whereas prescriptions for beta blockers were higher among non-Hispanic whites.
Regression models.—
In Model 1, adjusting for age and gender, blood pressure control was significantly lower among African Americans than non-Hispanic whites (odds ratio = 0.74, 95% confidence interval = 0.65–0.84; Table 3). Racial differences in blood pressure control were slightly reduced (odds ratio = 0.84, 95% confidence interval = 0.73–0.97) but remained significant after additional adjustment for income and education (Model 2). The association remained largely unchanged after adjustment for concurrent medical conditions (Model 3), obesity (Model 4), and antihypertensive medications (odds ratio = 0.81, 95% confidence interval = 0.70–0.94; Model 5). Addition of individual antihypertensive medication classes to our model did not change this association. We found no significant interactions between race and age, sex, education, or income, suggesting that racial differences in blood pressure control did not vary as a function of any of these factors.
Table 3.
Odds Ratios of Blood Pressure Control Among African Americans Relative to Non-Hispanic Whites.
| OR (95% CI) | |
| First model (adjusted for age and sex) | 0.74 (0.65–0.84) |
| Second model (adjusted for age, sex, education, and income) | 0.84 (0.73–0.97) |
| Third model (adjusted for age, sex, education, income, and medical conditions) | 0.81 (0.70–0.93) |
| Fourth model (adjusted for age, sex, education, income, medical conditions, and obesity) | 0.81 (0.70–0.93) |
| Fifth model (adjusted for age, sex, education, income, medical conditions, obesity, and antihypertensive medications) | 0.81 (0.70–0.94) |
Because the data for this analysis were collected over a period of more than 15 years, we explored potential temporal trends in racial differences in blood pressure control by adding an interaction term between race and cycle of data collection. There were no significant racial differences in blood pressure control rates at baseline (see Table 4). However, in all later data collection cycles, control rates improved substantially more among non-Hispanic whites than African Americans, leading to a growing disparity between the two racial groups.
Table 4.
Odds of Blood Pressure Control in African Americans Compared With Non-Hispanic Whites by Cycle of Data Collection.
| Data Collection Cycle | Blood Pressure Control (%) | Adjusted Odds Ratio* (95% CI) |
| 1993–1997 | ||
| African Americans (N = 1,791) | 766 (42.8) | 1.18 (0.99–1.42) |
| Non-Hispanic whites (N = 846) | 343 (40.5) | |
| 2001–2003 | ||
| African Americans (N = 942) | 441 (46.8) | 0.65 (0.47–0.92) |
| Non-Hispanic whites (N = 176) | 105 (59.7) | |
| 2003–2006 | ||
| African Americans (N = 463) | 245 (52.9) | 0.52 (0.38–0.70) |
| Non-Hispanic whites (N = 363) | 249 (68.6) | |
| 2006–2008 | ||
| African Americans (N = 170) | 80 (47.1) | 0.51 (0.30–0.89) |
| Non-Hispanic whites (N = 83) | 54 (65.1) |
*Adjusted for age, sex, education, income, and use of antihypertensive medications.
DISCUSSION
In this population-based study of older adults, we found that compared with non-Hispanic whites, African Americans had a higher prevalence and level of awareness of hypertension. Among those who reported being under treatment, the rate of blood pressure control was significantly lower for African Americans. Despite the substantial differences in SES between the two racial groups, adjustment for SES had only a small effect on racial differences in blood pressure control in this elderly population. Further adjustment for chronic medical conditions, obesity, and antihypertensive medications had no significant impact on racial differences in blood pressure control.
Although the overall prevalence of hypertension in our study was similar to that found in the National Health and Nutritional Examination Survey (NHANES) study, only half of the participants who reported being treated for hypertension had their blood pressures controlled, a rate lower than that reported in the NHANES (58% of the population 60 years or older and in 72% of younger adults) (1). The fact that NHANES participants are younger, on average, than those in this study and the fact that younger age is associated with better blood pressure control could explain the differences between our data and results from NHANES. We conjecture that the higher awareness of hypertension is related to an increased perceived risk by older African Americans.
We found substantial racial differences in blood pressure control in our study. Other studies have found similar differences (2,6,11,13–15). The one large study that has examined this question in an older population using NHANES data found no significant differences in blood pressure control between African Americans, non-Hispanic whites, and Mexican Americans on antihypertensive medications (1). The differences in the results between our analysis and the NHANES study could be explained by the use of only urban area participants in CHAP and the segregation of the neighborhoods in Chicago.
Few studies have focused on understanding the factors that contribute to these racial gaps in blood pressure control in older adults. Given that older adults have greater access to medical care and medication through Medicare, the factors that contribute to differences in blood pressure control may differ than those that matter in younger populations. One factor that has been shown to account for other racial disparities in health and health care is SES and in particular, differences in income and education (6). In our study, income and education had little impact on the racial differences in blood pressure control, suggesting that socioeconomic factors account for little of the racial differences in blood pressure control we found in older adults.
Other factors must account for observed differences in blood pressure control by race.
Bosworth and colleagues found that lack of medication adherence, medication side effects, and alternative health beliefs about hypertension were more prevalent in African Americans than whites and proposed these factors as a possible explanation for racial differences in blood pressure control (13). Differences in medication adherence may also be a factor. In a study addressing hypertensive medication compliance among elderly Medicaid enrollees, Monane and colleagues (16) found that older age and being white was associated with better medication adherence. Similarly, other studies have found poorer medication adherence among African Americans (17). Although not a proxy for medication adherence, we were able to control for antihypertensive medications that our participants said they were currently using, and this did not account for the racial gap in blood pressure control after adjusting for SES.
Other studies have examined the degree to which racial differences in health outcomes are related to inequalities in access to health care. While looking for racial differences in CVD indicators in older adults, Rooks and colleagues (2) suggested that racial differences in health care access and quality of care were associated with a higher prevalence of hypertension in black men. Although all participants in our study were Medicare eligible, this does not mean that enrollees have equal access to health care (18,19). Older black adults are more likely to experience psychosocial and structural barriers to health care access, such as lack of knowledge about available services, increased distance to health care facilities, and residence in segregated neighborhoods (20,21).
Finally, our exploratory analysis suggested an improvement in blood pressure control rates over time, which is possibly related to more aggressive treatment of high blood pressure in older adults in more recent years (22). Our data suggest that older non-Hispanic whites may have benefitted substantially more from improved blood pressure control than older African Americans. The slight drop in control rates in the last cycle may be due to a change in blood pressure assessment, when the CHAP study switched from a mercury sphygmomanometer to a digital device, which tends to produce slightly higher blood pressure readings (23). These findings remain inconclusive but suggest the need for a more systematic investigation of this issue in future studies of blood pressure control among older adults.
This study was not without limitations. It was a cross-sectional analysis of African Americans and whites in Chicago. Our samples were defined on self-reported data on awareness of hypertension and hypertension treatment. Although it may be seen as a limitation, this is the standard method used by other national studies of blood pressure, allowing for comparison across studies. An important strength of our analysis is that it involves a large population of older African Americans and non-Hispanic whites, with a reasonably wide spectrum of SES within each racial group. Due to these characteristics, we feel that our results can be generalized to similar urban populations in the United States.
Hypertension and CVD are important causes of morbidity and mortality in the elderly population. Our results indicate that racial disparities in blood pressure levels and hypertension control rates among older African Americans and non-Hispanic whites are likely an important contributor to disparities in CVD in the elderly population. They further suggest that these disparities place a particular burden on health care insurance programs such as Medicare. As socioeconomic factors did not seem to account for differences in blood pressure control, a focus on prevention and control strategies earlier in life may be needed to reduce disparities in later life, when elevated blood pressure may lead to more frequent serious medical complications, such as stroke and CHD.
FUNDING
This research was supported by grants from the National Institute on Aging (AG 11101, AG 032247, and AG 033172).
CONFLICT OF INTEREST
The authors have no conflicts of interest to report.
Acknowledgments
The authors thank Ms. Michelle Bos, Ms. Holly Hadden, Mr. Flavio Lamorticella, and Ms. Jennifer Tarpey for coordination of data collection; Mr. George Dombrowski for data management; and Mr. Zhaotai Cui for statistical programming.
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