From the Department of Biostatistics and Epidemiology, Tulane University
School of Public Health and Tropical Medicine, New Orleans, La (J.H., P.K.W.);
the Welch Center for Prevention, Epidemiology, and Clinical Research (M.J.K.,
L.J.A.) and the Departments of Medicine (M.J.K., L.J.A.) and Epidemiology
(M.J.K., L.J.A., J.C.), the Johns Hopkins Medical Institutions, Baltimore, Md.
One of the first studies to compare BP between African Americans and
whites in a community sample was conducted in Muscogee County, Georgia,
by Comstock.8 In his study, Comstock found that
African Americans had higher BP levels than whites at every age
studied. Many subsequent investigations, including several national
surveys of US residents conducted by the National Center for Health
Statistics, confirmed that African Americans have higher BP levels as
well as a higher prevalence of hypertension than
whites.9 10 11 12 In most studies, the prevalence of
hypertension was about 50% higher in African Americans than in
whites.
Several longitudinal studies have also shown that African Americans
have a higher incidence of hypertension than
whites.1 2 3 4 5 However, this racial difference in
the risk of hypertension may be modified by age. In the NHANES I
Epidemiologic Follow-up Study, the incidence of hypertension in African
Americans was over two times higher than in whites among those aged 25
to 34 years. In contrast, the incidence of hypertension did not differ
between African Americans and whites who were 55 years of age or
older.1 In other studies conducted in young
adults, the incidence of hypertension in African Americans was an
average of two times higher than in
whites.3 4 5
The purpose of the present study was to compare the incidence of
hypertension between African Americans and whites who had similar BPs
at baseline and to identify risk factors for developing
hypertension.
Baseline Data Collection
Nine BP measurements, three at each of the three screening visits, were
obtained at baseline. BP measurements were obtained using the Hawksley
random-zero modification of the standard mercury
sphygmomanometer.16 BP was measured after the
individual had been seated quietly for 5 minutes. The subject was
instructed not to eat or smoke for at least 30 minutes before their BP
measurements. The first and fifth Korotkoff sounds were recorded as
systolic and diastolic pressure, respectively. Body
weight and height were measured at screening visit 1, and BMI
(kg/m2) was calculated as an index of
obesity.17
Follow-up Data Collection
Hypertension at follow-up was defined as diagnosis of hypertension by a
physician during the follow-up period and initiation of
antihypertensive therapy as assessed by questionnaire
and/or2 systolic BP
Statistical Analysis
Baseline Characteristics of African American and White
Participants
Average age, BP, and BMI were similar in the African Americans and
whites because of the study's eligibility criteria. African Americans
had slightly lower physical activity measured by the number of times
per week a person exercised enough to perspire, albeit this difference
was not statistically significant. Ratios of urinary sodium to
creatinine and potassium to creatinine were
significantly lower in the African Americans compared with the whites,
while the corresponding ratio of urinary sodium to potassium was not
significantly different. The racial differences in baseline
characteristics were similar in men and women.
Incidence of Hypertension in African American and White
Participants
African Americans and whites had similar crude odds of developing
hypertension (Table 2
Likewise, changes in BP over the period of follow-up were not
statistically significantly different between African Americans and
whites (gender-adjusted systolic: 1.6 mm Hg in African
Americans versus 1.9 mm Hg in whites, P=.8;
gender-adjusted diastolic: -5.6 mm Hg in African
Americans and -5.8 mm Hg in whites, P=.9). After
further adjustment for other risk factors, these differences remained
not significant.
Relationship of Baseline Characteristics to Risk of
Hypertension
Baseline BP was strongly related to the odds of hypertension in all
groups. For example, a 9.3 mm Hg higher systolic pressure
at baseline was associated with a 2.98-fold greater odds of developing
hypertension in African Americans and a 2.60-fold greater risk in
whites. Likewise, a 4.2 mm Hg higher diastolic
pressure was associated with 2.51 times higher odds of developing
hypertension in African Americans and 2.96 times higher odds in whites.
The magnitude of the elevated odds for hypertension related to baseline
BP was similar for African Americans and whites (P values
for test of interaction: 0.65 for systolic and 0.57 for
diastolic pressure). After adjustment for gender, ORs of
hypertension associated with baseline BP remained similar in African
Americans compared with whites. Baseline heart rate was positively
related to the odds of developing hypertension in whites and the total
sample, while baseline BMI was related to the odds of developing
hypertension in African Americans only (Table 3
The results from multivariate logistic regression
models are presented in Table 4
Relationship of Baseline Characteristics to Changes in BP
A BMI higher by 1 SD (3.7 kg/m2) at baseline was
associated with a greater increase in systolic pressure during
follow-up in the African Americans (3.0 mm Hg, P<.01)
and the combined sample (1.3 mm Hg, P<.05). An
increase of 1 SD in BMI during follow-up (1.98
kg/m2) was positively related to change in both
systolic and diastolic pressures among the African
Americans (2.8 and 1.6 mm Hg, both P<.05), whites
(2.7 and 2.1 mm Hg, both P<.001), and the combined
sample (2.9 and 1.9 mm Hg, both P<.001). In
regression models including both BMI at baseline and its change during
follow-up, only change during follow-up was significantly associated
with change in BP. Average BPs measured at baseline and at the
follow-up visit were significantly related to change in BP during
follow-up among all groups. For example, average systolic
pressure higher by 1 SD (9.3 mm Hg) was associated with an
increase in systolic pressure during follow-up of 5.4, 5.9, and
5.7 mm Hg for African Americans, whites, and the combined sample,
respectively (all P<.001). Average diastolic
pressure higher by 1 SD (5.0 mm Hg) was associated with an
increase in diastolic pressure during follow-up of 4.3,
5.0, and 4.7 mm Hg for African Americans, whites, and the
combined sample, respectively (all P<.001). The magnitude
of this relationship did not differ significantly between African
Americans and whites (P=.67 for systolic and
P=.30 for diastolic).
In multivariate linear regression analysis,
age, gender, ethnicity, intervention assignment in TOHP-1, baseline
alcohol consumption, change in BMI during follow-up, and average BP
measured at baseline and at the follow-up visit explained about 31% of
the variation in systolic pressure change and 50% of the
variation in diastolic pressure change during follow-up. In
that model, on average, women had a 3.9 mm Hg greater increase in
systolic pressure than men (P<.01) during
follow-up. Changes in BMI over time were positively related to
corresponding changes in systolic and diastolic
pressures. For example, a 1.98 kg/m2 increase in
BMI was related to a 2.3 mm Hg increase in systolic
pressure (P<.001) and a 1.7 mm Hg increase in
diastolic pressure (P<.001) during follow-up. A
difference of 9.3 mm Hg in the average systolic pressure
measured at baseline and at follow-up visit was related to an increase
of 5.2 mm Hg in systolic pressure (P<.001)
during the 7 years of follow-up, while a 5.0 mm Hg difference in
average diastolic pressure was related to an increase of
4.7 mm Hg in diastolic pressure
(P<.001).
These findings are different from those of several previous studies
that demonstrated an elevated risk of hypertension in African Americans
compared with whites.8 9 10 11 12 20 21 22 23 However, in the
NHANES I Epidemiologic Follow-up Study, the only longitudinal study of
the age-specific incidence of hypertension by race, African Americans
and whites had a similar risk of hypertension after age
55.1 In the present investigation, the study
participants were middle-aged and had a relatively high normal
diastolic pressure when they entered the study. The
distributions of age, BMI, heart rate, and BP at baseline were almost
identical between African American and white participants.
Some studies have suggested that African Americans develop
hypertension at an earlier age than whites.24 25 26
Manatunga and colleagues followed 164 African American and 345 white
children for 2 to 5.5 years.26 They found that
the African American children had a significantly higher mean BP and
rate of increase in BP over time. Earlier puberty and weight gain in
African American children may partly explain the difference in
BP.26 Given the higher overall risk of
hypertension in African Americans compared with whites, the results
from our study are consistent with other
studies1 3 25 26 suggesting that the excess
burden of hypertension in African Americans may be due primarily to a
higher BP level and rise in BP with age in adolescence and young
adulthood. Efforts to prevent high BP and its sequelae in African
Americans need to target groups before they reach middle age.
In the present study, most of the participants were employed and
had a relatively high socioeconomic status compared with general
population. Lower socioeconomic status and a lower standard of health
care have been proposed as possible explanations for the excess risk of
hypertension in African Americans. The high socioeconomic status of the
present study population may have also been partially responsible
for the similar incidence of hypertension in the African American and
white participants.
In the present study, women had a higher incidence of hypertension
and greater increase in BP over time than men. These results may
reflect the distribution of age and initial BP in this cohort. Several
studies have demonstrated that men have a higher risk of hypertension
in early adulthood. In contrast, women have a higher risk of
hypertension in later life.1 27
In contrast to many previous studies,28 29 30
baseline BMI was not a strong predictor of the incidence of
hypertension among whites in this study. However, longitudinal change
in BMI was positively associated with an increase in BP over follow-up,
independent of other important risk factors for hypertension. This
finding suggests that gain in body weight over time may be a more
important risk factor for high BP than a participant's initial body
weight at baseline.
Despite the narrow range of baseline BP in this cohort, both
systolic and diastolic pressures at baseline were
significantly related to subsequent risk of hypertension. In addition,
the average BP over follow-up was a significant predictor of subsequent
change in BP. The predictive value of baseline systolic or
diastolic pressure on subsequent hypertension was not only
independent of important risk factors—such as age, gender, race,
alcohol consumption, body mass, heart rate, and intervention assignment
in TOHP-1—but also of each other. The increased risk of hypertension
in those with a higher initial BP warrants greater preventive effort in
this group.
The limitations of the present study were that many of the study
participants were recruited at work sites and thus had a relatively
high socioeconomic status. Study entrance criteria restricted
participants by age and initial BP, resulting in groups with similar
characteristics. However, these similarities allowed for comparison of
the incidence of hypertension in middle-aged African Americans and
whites without confounding by these important factors.
In summary, the present study indicates that middle-aged African
Americans and whites have a similar risk of developing hypertension
given the same age, level of BP, and BMI at baseline.
Received August 25, 1997;
first decision September 22, 1997;
accepted December 23, 1997.
2.
Apostolides AY, Cutter G, Daugherty SA, Detels R,
Kraus J, Wassertheil-Smoller S, Ware J. Three-year incidence of
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Johnson AL, Cornoni JC, Cassel JC, Tyroler HA, Heyden
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6.
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7.
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Brancati FL, Shulman NB, Stamler J. Race and incidence of ESRD: a
prospective study. Circulation. 1994;89:8. Abstract.
8.
Comstock GW. An epidemiologic study of blood pressure
levels in a biracial community in the Southern United States.
Am J Hyg. 1957;65:271–315.[Medline]
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9.
National Center for Health Statistics, Gordon T. Blood
pressure of adults by age and sex, United States, 1960-62. Vital
Health Stat. 1964; series 11: No. 4. US Public Health Service
publication 1000.
10.
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pressure of persons 18-74 years, United States, 1971-72. Vital
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Education, and Welfare (HRA) publication 72-1632.
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Dannenberg AL, Engel A. Blood pressure levels in persons 18-74 years of
age in 1976-80 and trends in blood pressure from 1960-1980 in the
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12.
Burt VL, Whelton PK, Roccella EJ, Brown C, Cutler JA,
Higgins M, Horan MJ, Labarthe D. Prevalence of hypertension in the US
adult population: results from the third National Health and Nutrition
Examination Survey, 1988–1991. Hypertension. 1995;25:305–313.
13.
Satterfield S, Cutler JA, Langford HG, Applegate WB,
Borhani NO, Brittain E, Cohen JD, Kuller LH, Lasser NL, Oberman A,
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pressure of persons with high normal levels: results of the Trials of
Hypertension Prevention, phase 1. JAMA.. 1992;267:1213–1220.
15.
Paffenbarger RS Jr, Wing AL, Hyde RT. Physical activity
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measurements of the same subjects. J Chronic Dis. 1962;15:969–977.[Medline]
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21.
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Cooperative Group. Race, education and prevalence of hypertension.
Am J Epidemiol. 1977;106:351–361.
22.
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S, Davis CE, Tyroler HA. Gender differences in multiple risk factor
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© 1998 American Heart Association, Inc.
Scientific Contributions
Seven-Year Incidence of Hypertension in a Cohort of Middle-Aged African Americans and Whites
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Abstract—Many studies have suggested
that African Americans have a higher prevalence of hypertension than
whites. The authors conducted a prospective study of hypertension
incidence from 1987-1988 to 1994-1995 in 140 African American and 237
white adults aged 30 to 54 years at baseline. The study participants
were screened for participation in the Trials of Hypertension
Prevention, phase 1, an 18-month lifestyle modification intervention
trial aimed at lowering blood pressure, at the Baltimore Clinical
Center. Baseline age, blood pressure, body mass index, and heart rate
were similar in the two groups. Compared with whites, however, African
Americans had a lower percentage of men, college graduates, and
households with an income 
$40 000 per year. African Americans also
had lower mean urinary sodium to creatinine ratio and
potassium to creatinine ratio, but a similar sodium to
potassium ratio. The incidence of hypertension (blood pressure
160/95 mm Hg and/or taking antihypertensive medication) over 7
years of follow-up was nearly identical: 25.7% in African Americans
and 25.3% in whites. Baseline age, gender, blood pressure, and heart
rate were all associated with the incidence of hypertension. Even after
adjustment for these covariables, the risk of hypertension was not
higher in African Americans compared with whites. These results
indicate that middle-aged African Americans and whites have a similar
risk of developing hypertension given the same age, initial blood
pressure, and body mass index at baseline.
Key Words: blacks • blood pressure • ethnicity • incidence
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
Hypertension is an
important public health challenge in the United States, especially
among African Americans. In general, African Americans are at higher
risk of hypertension and its complications than are other ethnic
groups.1 2 3 4 5 6 7
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Study Participants
The study population consisted of 463 screenees (171 African
Americans and 292 whites) from the Baltimore clinic center of the
TOHP-1. The TOHP-1 was a national, multicenter, randomized, controlled
trial designed to test the short-term feasibility and efficacy of three
lifestyle (weight loss, sodium restriction, and stress management) and
four nutritional supplement (calcium, magnesium, fish oil, and
potassium) interventions aimed at lowering diastolic
pressure in those whose BP was initially in the high normal range (80
to 89 mm Hg).13 14 Most of the study
participants were identified through a work-site screening program
conducted from September 1987 through October 1988. The participants
primarily came from the Social Security Administration and the Health
Care Financing Administration headquarters located in western
Baltimore. Of the 463 screenees, 286 were randomly allocated to the
trial. The major reasons for not randomizing those who were screened
were presence of a mean diastolic BP 
80 mm Hg or a
decision by the participant. The principal eligibility criteria for
study participation in TOHP-1 included age between 30 and 54 years and
no evidence of medically diagnosed hypertension or other
cardiovascular disease, extreme obesity (BMI 36.1
kg/m2), or heavy alcohol use (21 drinks per
week).13 14
Baseline observations were obtained at three screening
visits.13 All data were carefully collected by
specially trained, experienced observers using standardized methods and
a stringent level of quality control. All data collectors passed an
initial series of certification examinations as well as periodic
recertification evaluations. Demographic information, medical history,
and health habit data were collected at screening visit 1.
Physical activity was assessed with the Harvard Alumni Physical
Activity Questionnaire at visit 2, which ascertains both work and
leisure physical activity and the frequency of vigorous exercise
resulting in perspiration each week.15 One
24-hour urine specimen was collected at screening visit 3 for
estimation of sodium, potassium, and creatinine
content.
The follow-up study was conducted between November 1994 and
September 1995. Medical history, especially personal history of
hypertension and use of antihypertensive medication, was evaluated by
questionnaire. Three BP measurements were obtained using the same
method as for the baseline visits. Body weight, height, and waist and
hip girths were also measured at the follow-up visit. 160 mm Hg
and/or3 diastolic BP 95 mm Hg
at the follow-up examination. A mean BP 160/95 mm Hg was used
as the cut point for definition of hypertension in the present
study because the follow-up BP measurements were obtained at only one
visit. Furthermore, the presence of a systolic BP <160
mm Hg was used as an eligibility criterion for inclusion in
TOHP-1.
Incidence of hypertension was expressed as the proportion of
hypertensives in all study participants seen at follow-up. The racial
differences in the incidence of hypertension or its risk factors were
examined using 
2 or Student's t
tests. Logistic regression analysis was used to compare the
risk of hypertension between African Americans and whites after
adjustment for other risk factors. Univariate and
multivariate logistic regression analyses also
were used to explore the relationship between baseline characteristics
and risk of hypertension. Linear regression analysis was used
to examine the relationship between these baseline characteristics and
changes in BP level over follow-up. Study participants who were taking
antihypertensive medications at the follow-up visit were excluded from
the linear regression analysis because their BP level before
initiation of antihypertensive medication was not available. OR or
regression coefficients associated with a difference of 1 SD in
continuous independent variables were reported. Assignment to
sodium reduction or weight loss interventions in TOHP-1 was associated
with the risk of hypertension during follow-up. Therefore, intervention
assignment in TOHP-1 was included as a covariable in all
multivariate analyses. To avoid possible bias
due to regression toward the mean, the average of BP measured at
baseline and at follow-up was used to predict change in
BP.18 All analyses were performed using
SAS software.19
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Of the 463 African American and white TOHP-1 screenees, 377
(81.4%) participated in the follow-up study. Among the 86
nonrespondents, 1 was deceased, 3 were seriously ill, and the remaining
82 refused to participate. Nonrespondents and respondents had similar
baseline characteristics including race, gender, socioeconomic status
(education and employment), health habits (cigarette smoking, alcohol
consumption, and physical activity), body weight, heart rate, and BP.
However, nonrespondents were an average of 1.5 years younger than the
respondents (P=.02).
Table 1
shows baseline
characteristics of the study participants by race. Because the
proportion of male participants was significantly lower in African
Americans than in whites, all analyses were adjusted for sex.
African Americans were less educated and had lower household incomes
than whites, although all study participants had a relatively high
socioeconomic status. Compared with the whites, more African Americans
were employed full-time. The proportion of study participants who were
married, were current cigarette smokers, drank alcohol, or were
allocated to sodium or weight reduction interventions in TOHP-1 was not
statistically significantly different between African Americans and
whites.
View this table:
[in a new window]
Table 1. Baseline Characteristics of Study Participants by
Race, Baltimore, 1987–19951
The average period of follow-up was 7.1 years (ranging from 6.3 to
7.9 years) and was similar in the African American and white
participants. At the follow-up visit, 36 African Americans and 60
whites reported a history of hypertension since their screening
examination in 1987-1988 and were taking antihypertensive medication or
met the BP criteria for diagnosis of hypertension. The overall
incidence of hypertension was 25.7% for African Americans and 25.3%
for whites. ). After adjustment
for gender, the OR was reduced from 1.02 to 0.62, but this was still
not significantly different from 1. After further adjustment for age,
income, alcohol consumption, intervention assignment in TOHP-1, BMI,
heart rate, and BP at baseline, the OR changed very little. The ORs
adjusted for urinary sodium and potassium are not listed in Table 2
because they were calculated using a smaller sample size. The OR
adjusted for gender and ratio of urinary sodium to
creatinine was 0.68 (95% CI, 0.37 to 1.25), and the OR
adjusted for gender and ratio of urinary potassium to
creatinine was 0.68 (95% CI, 0.37 to 1.27),
respectively.
View this table:
[in a new window]
Table 2. OR of Hypertension in African Americans Compared
With Whites in 377 Study Participants, Baltimore, 1987–1995
Univariate ORs of hypertension associated with
baseline characteristics, overall and by race, are presented in
Table 3. Age was associated with an
increased odds of developing hypertension in the total sample as well
as in whites. Age was not significantly associated with the odds of
hypertension in African Americans, and a test for interaction between
age and race in the odds of hypertension was not significant
(P=.11). Female gender was a significant predictor of
hypertension in both races.
View this table:
[in a new window]
Table 3. OR (95% CI) of Hypertension Associated With 1 SD
Difference in Baseline Characteristics Among African American and
White Study Participants, Univariate Logistic Regression
Analysis, Baltimore, 1987–1995 
). However, racial
differences in the relationship of heart rate and BMI to the odds of
developing hypertension did not achieve statistical significance. .
Analyses were conducted in the total sample because no
significant interaction was detected between the effect of race and
baseline characteristics on the odds of hypertension. In model 1, where
baseline BP was not included, age and baseline heart rate were related
to an increased odds of hypertension. Men had lower odds of developing
hypertension than women. Baseline BP was introduced to model 2. In this
model, age and heart rate were no longer significantly associated with
odds of hypertension, but baseline systolic and
diastolic pressures independently predicted odds of
hypertension. Systolic pressure higher by 1 SD (9.3
mm Hg) was related to a 79% increase in the odds of hypertension,
whereas diastolic pressure higher by 1 SD (4.2 mm Hg)
was associated with a 2.19-fold increase in the odds of
hypertension.
View this table:
[in a new window]
Table 4. OR of Hypertension Associated With 1 SD Difference
in Baseline Characteristics Among 377 Study Participants, Multiple
Logistic Regression Analysis, Baltimore, 1987–19881
Over the 7 years of follow-up, systolic pressure increased
by an average of 2.6 mm Hg, but diastolic pressure
decreased by 5.1 mm Hg in the 110 African American and 183 white
participants who were not taking antihypertensive medications. A
5.8-year older age was significantly associated with a greater increase
in systolic pressure during follow-up in whites (2.7
mm Hg, P<.01) and in the combined group (1.7 mm Hg,
P<.05). Women had a significantly greater increase in
systolic pressure than men during follow-up in African
Americans (5.1 mm Hg, P<.05), whites (6.4
mm Hg, P<.01), and the combined group (5.7 mm Hg,
P<.001). Graduation from a 4-year college was inversely
associated with an increase in systolic pressure in the African
Americans (-5.4 mm Hg, P<.05) but not in the whites
(0.27 mm Hg, P=.9). A test for interaction between
race and education on systolic pressure was of borderline
statistical significance (P=.06). Higher household income
was inversely associated with an increase in systolic pressure
over time in all groups, but this was significant only in the combined
group (-3.5 mm Hg, P<.05). However, neither
education nor income was significantly related to change in
systolic pressure over time after adjustment for gender (data
not shown).
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
In the present study, middle-aged African Americans did not
have a higher incidence of hypertension over a 7-year
follow-up period compared with whites with a similar age,
initial BP, and BMI. Mean change in BP over time was also not
significantly different in the two ethnic groups. Furthermore, the
magnitude of increases in the odds of hypertension associated with
baseline BP level was similar in African Americans compared with
whites.
Selected Abbreviations and Acronyms
BP
=
blood pressure
CI
=
confidence interval
OR
=
odds ratio
TOHP-1
=
Trials of Hypertension Prevention, phase 1
Acknowledgments
This study was supported by an American Heart
Association–Maryland Affiliate Grand-in-Aid (MDBG1195) and partially
by Outpatient General Research Center grant 5M01RR00722 from the
National Institutes of Health. Dr He was supported by training grant
5T32HL07024-21 from NIH National Heart, Lung, and Blood Institute. The
authors would like to thank study coordinator Dolores Kaidy and
research technicians Sharon Capelli, Shirley George, Charles Harris,
Vicki Harris, Estelle Levitas, Selma Schlenhoff, and Bobbie Weiss at
the Johns Hopkins Pro-Health Research Office for their excellent
technical assistance during this project.
Footnotes
Reprint requests to Jiang He, MD, PhD, Department of Biostatistics and Epidemiology, Tulane University School of Public Health and Tropical Medicine, 1430 Tulane Ave SL18, New Orleans, LA 70112-2699.
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
1.
Cornoni-Huntley J, LaCroix AZ, Havlik RJ. Race and
sex differentials in the impact of hypertension in the United States:
the National Health and Nutrition Examination Survey I Epidemiologic
Follow-up Study. Arch Intern Med. 1989;149:780–788.
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