Original article
Is the Association of Diabetes With Uncontrolled Blood
Pressure Stronger in Mexican Americans and Blacks
Than in Whites Among Diagnosed Hypertensive Patients?
Xuefeng Liu1 and Ping Song2
background
Clinical evidence shows that diabetes may provoke uncontrolled blood
pressure (BP) in hypertensive patients. However, racial differences in
the associations of diabetes with uncontrolled BP outcomes among
diagnosed hypertensive patients have not been evaluated.
methods
A total of 6,134 diagnosed hypertensive subjects aged ≥20 years were
collected from the National Health and Nutrition Examination Survey
1999–2008 with a stratified multistage design. Odds ratios (ORs) and
relative ORs of uncontrolled BP and effect differences in continuous BP
for diabetes over race/ethnicity were derived using weighted logistic
regression and linear regression models.
results
Compared with participants who did not have diabetes, non-Hispanic black participants with diabetes had a 138% higher chance
of having uncontrolled BP, Mexican participants with diabetes had
a 60% higher chance of having uncontrolled BP, and non-Hispanic
white participants with diabetes had a 161% higher chances of
having uncontrolled BP. The association of diabetes with uncontrolled BP was lower in Mexican Americans than in non-Hispanic
blacks and whites (Mexican Americans vs. non-Hispanic blacks:
relative OR = 0.55, 95% confidence interval (CI) = 0.37–0.82;
Mexican Americans vs. non-Hispanic whites: relative OR = 0.53,
95% CI = 0.35–0.80) and the association of diabetes with isolated
uncontrolled systolic BP was lower in Mexican Americans than in
non-­Hispanic whites (Mexican Americans vs. non-Hispanic whites:
relative OR = 0.62, 95% CI = 0.40–0.96). Mexican Americans have
a stronger associaton of diabetes with decreased systolic BP and
­diastolic BP than non-Hispanic whites, and a stronger association of
diabetes with decreased diastolic BP than non-Hispanic blacks.
conclusions
The association of diabetes with uncontrolled BP outcomes is lower
despite higher prevalence of diabetes in Mexican Americans than in nonHispanic whites. The stronger association of diabetes with BP outcomes
in whites should be of clinical concern, considering they account for the
majority of the hypertensive population in the United States.
Keywords: blood pressure; diabetes; diagnosed hypertension; hypertension; isolated uncontrolled diastolic blood pressure; isolated
uncontrolled systolic blood pressure; racial disparity; uncontrolled
blood pressure.
doi:10.1093/ajh/hpt109
High blood pressure (BP) or hypertension is a major risk
factor for adverse cardiovascular and renal outcomes.1–5
Approximately 3.8 million premature deaths and 46 million
disability-adjusted life-years worldwide are attributable to
hypertension.6 The treatment of hypertension has been one
of medicine’s major successes of the past decades.7 Although
remarkable advances in therapy have provided the capability
for lowering BP in persons with hypertension, hypertension
continues to be a major public health concern. Lack of BP
control dramatically increases cardiovascular and renal diseases among hypertensive patients.3,8,9
Racial/ethnic background affects cardiovascular risk factors and control rates of hypertension and partly explains
the paradox that the control of hypertension continues to
be inadequate despite advances in effective medications
and therapy. To have overall rates of controlled hypertension increased, major strategies are being directed toward
improving access to medical care in disadvantaged minority
groups because of the racial differences in cardiovascular risk
factors and uncontrolled BP among hypertensive patients.10
Diabetes mellitus (DM) coexists with hypertension and has
been linked to BP control.11–14 The prevalence of DM is commonly higher in blacks and Hispanics than in whites in both
the general population and the specific hypertensive population.10,15,16 Whether blacks and Hispanics with DM are more
likely to have uncontrolled BP than whites with DM has not
been investigated. Many investigators believe the association of DM with uncontrolled BP is stronger in blacks and
Hispanics than in whites. However, this might not be true
for diagnosed hypertensive patients with some treatment.
Correspondence: Xuefeng Liu ([email protected]).
1Department of Biostatistics and Epidemiology, College of Public Health,
East Tennessee State University, Johnson City, Tennessee; 2Department
of Internal Medicine, College of Medicine, University of Oklahoma
Health Sciences Center, Oklahoma City, Oklahoma.
Initially submitted February 6, 2013; date of first revision May 21, 2013;
accepted for publication June 10, 2013; online publication July 17, 2013.
© American Journal of Hypertension, Ltd 2013. All rights reserved.
For Permissions, please email: [email protected]
1328 American Journal of Hypertension 26(11) November 2013
Diabetes and Hypertension Control
In this study, the association of DM with uncontrolled
and/or continuous BP was examined among non-Hispanic
blacks, Mexican Americans, and non-Hispanic whites with
diagnosed hypertension using the continuous National
Health and Nutrition Examination Survey (NHANES)
data from the period 1999–2008. We hypothesized that the
association of DM with uncontrolled BP differed, and the
discrepancy between the prevalence of DM and the association of DM with uncontrolled BP would exist among
diagnosed hypertensive patients in the studied racial populations. Because differences in the uncontrolled rates over
race may be attributed to racial differences in cardiovascular risk factors, our goal was to identify racial disparities in
the relationships of DM with uncontrolled BP outcomes.
These differences would allow the targeting of race-specific
relations to better control BP and thereby reduce the risk of
cardiovascular disease–related morbidities and mortality
among hypertensive patients.
defined as having SBP ≥ 140 mm Hg and DBP < 90 mm Hg in
nondiabetic subjects or having SBP ≥ 130 mm Hg and DBP
< 80 mm Hg in diabetic subjects, and isolated uncontrolled
DBP as having DBP ≥ 90 mm Hg and SBP < 140 mm Hg in
nondiabetic subjects or having DBP ≥ 80 mm Hg and SBP
< 130 mm Hg in diabetic subjects, according to the Seventh
Report of the Joint National Committee on Prevention,
Detection, Evaluation and Treatment of High Blood Pressure
(JNC7).21 We noticed that the American Diabetes Association
published the latest standards of medical care in diabetes in
early 2013 in which the new goals of BP control for people
with diabetes had changed to < 140/80 mm Hg, with the
exception of younger patients for whom 130/80 mm Hg may
be appropriate if it can be achieved without undue treatment
burden. Because NHANES data we used in the study were
collected during the period 1999–2008, we still followed the
JNC7 guidelines on BP control.
Diabetes mellitus
METHODS
Study design and participants
The continuous NHANES program, conducted by the
National Center for Health Statistics in the Centers for
Disease Control and Prevention (CDC), has included a
series of 2-year, cross-sectional, nationally representative
health interview and examination surveys with a complex,
stratified, multistage probability cluster sampling design.
All of the participants gave informed consent, and the study
received approval from the CDC Institutional Review Board.
The detailed measurement procedures and protocols can be
found on the NHANES website (http://www.cdc.gov/nchs/
about/major/nhanes/datalink.htm).
For this study, we combined data (n = 50,844) from
NHANES for the period 1999–2008. Participants aged
< 20 years who were interviewed but not examined
(n = 26,151), who were not non-Hispanic whites, nonHispanic blacks or Mexican Americans (n = 2,369), who
were pregnant women (n = 1,016), and who were not diagnosed as hypertensive patients (n = 15,174) were excluded
from the study. A total of 6,134 participants with diagnosed
hypertension were included in the final sample.
Definitions of BP outcomes
Systolic BP (SBP) and diastolic BP (DBP) were measured
up to 4 times manually by trained physicians using mercury
sphygmomanometers and appropriately sized arm cuffs after
participants rested 5 minutes in a seated position.17–20 The
final SBP and DBP were calculated as the averages of SBP
and DBP measurements for each individual. Participants
were defined to have diagnosed hypertension if 1) they were
currently taking prescribed medications for hypertension
or 2) they self-reported hypertension diagnosed by a doctor
that was further confirmed by elevated BP (average SBP ≥
140 mm Hg or average DBP ≥ 90 mm Hg). Uncontrolled BP
was determined as having SBP ≥ 140 mm Hg or DBP ≥ 90 mm
Hg in nondiabetic persons and SBP ≥ 130 mm Hg or DBP ≥
80 mm Hg in diabetic persons. Isolated uncontrolled SBP was
DM was determined by clinical measurements on glycohemoglobin levels and a positive response to any of the
following questions: “Have you ever been told by a doctor
that you have diabetes?”; “Are you now taking insulin?”; “Are
you now taking diabetes pills to lower your blood sugar?”16,22
Participants were defined to have DM if they were taking
medications for diabetes or had been told by a doctor that
they have diabetes, with the diagnosis further confirmed by
elevated level of glycohemoglobin ≥ 6.5%.
Other characteristics
Information on age, sex, race/ethnicity, and education
was self-reported. The family’s poverty income ratio was
calculated by dividing family total income by poverty
threshold, which was a guideline specific to family size as
well as the appropriate year and state, issued each year by
the Department of Health and Human Services. History
of smoking was obtained from household interview
for participants aged ≥ 20 years. Body mass index was
calculated as weight in kilograms divided by the square of
height in meters. Pregnancy was determined in women by
a self-reported questionnaire and a urine pregnancy test.
A participant was defined to have high cholesterol if his or her
serum cholesterol was ≥ 200 mg/dl. The levels of albuminuria
were determined by a urinary albumin/creatinine ratio.
Participants were defined as having microalbuminuria if
the urinary albumin/creatinine ratio was ≥ 30 mg/g and
< 300 mg/g and as having macroalbuminuria if the urinary
albumin/creatinine ratio was ≥ 300 mg/g.23 Urinary albumin
was measured in a solid-phase fluorescent immunoassay
using a Sequoia-Turner fluorometer (Mountain View, CA).
Urinary creatinine was measured colorimetrically by a Jaffé
rate reaction on a Beckman Synchron AS/ASTRA clinical
analyzer (Beckman Instruments, Brea, CA).
Statistical analysis
Stratum, cluster, and weight design techniques for survey
data were considered to incorporate sampling weights into
American Journal of Hypertension 26(11) November 2013 1329
Liu and Song
data analysis. Means or percentages and 95% confidence
intervals (CIs) were calculated to examine differences in
characteristics of participants with diagnosed hypertension over DM status and over racial groups of non-Hispanic
blacks, Mexican Americans, and non-Hispanic whites. Mean
or percentage differences were tested for significance by
using χ2 statistics for categorical variables and Wald tests for
continuous variables. The means or rates of risk factors were
all age-adjusted by direct standardization to the NHANES
1999–2008 population with diagnosed hypertension except
for age-specific factors.
After adjustment for potential confounding factors
(age, sex, education, family poverty income ratio, smoking status, body mass index, serum cholesterol, albuminuria), adjusted odds ratios (ORs) of uncontrolled BP,
isolated uncontrolled SBP, and isolated uncontrolled DBP
were obtained from weighted logistic regression models to
examine the risks of uncontrolled BP, SBP, and DBP associated with DM; regression coefficients of DM on continuous
SBP and DBP were obtained from multiple linear regression models to examine how continuous BP differs over
DM status in individual racial groups. To test the significance of racial differences in the associations of DM with
uncontrolled BP and continuous BP, relative ORs of uncontrolled BP, SBP, and DBP (categorical endpoints) and effect
differences in continuous SBP and DBP for DM were calculated from weighted multiple logistic models and weighted
multiple linear models, respectively, by adding race, DM,
and interaction of race and DM in the models. In this study,
the relative ORs were calculated as the ORs of uncontrolled
BP, SBP, and DBP for DM in 1 racial group divided by the
corresponding ORs in another racial group; effect differences were derived as differences in the effects of DM on
continuous SBP and DBP between racial groups. All the
data analyses were performed on windows 7 PC by using
SAS version 9.2 (SAS Institute, Cary, NC).
RESULTS
The average age of the study population was 60.54 ± 0.33 years. After adjustment for age, 56.27 ± 0.79% of participants were women; 14.64 ± 1.28% were non-Hispanic
blacks, and 3.76 ± 0.56% were Mexican Americans. The overall rates of DM and uncontrolled BP were 24.49 ± 0.78% and
50.82 ± 0.95%, respectively.
Characteristics of the study population by DM and race in
NHANES 1999–2008 is presented in Table 1. We can see that
on the average, persons with DM were older and poorer and
more likely to be in school < 12 years compared with nondiabetic subjects (P < 0.001). The average body mass index,
the prevalence of microalbuminuria and macroalbuminuria,
and the rate of taking antihypertensive drugs were higher
in diabetic subjects than in those without DM (P < 0.001).
However, the rate of alcohol use (P < 0.01), the average of
serum cholesterol levels (P < 0.01), and the prevalence of
high cholesterol (P < 0.001) were lower in diabetic subjects
than in nondiabetic subjects.
In this study, non-Hispanic whites were older and had a
higher rate of former smoking than non-Hispanic blacks
and Mexican Americans (P < 0.001). More women than men
1330 American Journal of Hypertension 26(11) November 2013
had diagnosed hypertension in each of the racial groups;
this was especially the case for non-Hispanic blacks. Overall,
Non-Hispanic blacks and Mexican Americans were poorer,
received less education, and had greater mean body mass
index and higher obesity rate than non-Hispanic whites
(P < 0.001). The prevalence of DM, microalbuminuria, and
macroalbuminuria was highest in Mexican Americans and
lowest in non-Hispanic whites.
After adjustment for potential risk factors, hypertensive
participants with DM were more likely to have uncontrolled
BP, isolated uncontrolled SBP, and lower average DBP (last
column in Table 2). Separate analysis showed that DM was
associated with higher odds of uncontrolled BP by 2.38
(95% CI = 1.77–3.18) times in non-Hispanic blacks, 1.60
(95% CI = 1.01–2.52) times in Mexican Americans, and
2.61 (95% CI = 2.02–3.38) times in non-Hispanic whites.
DM was also significantly associated with the increased
odds of isolated uncontrolled SBP in non-Hispanic blacks
(OR = 1.90, 95% CI = 1.27–2.83) and non-Hispanic whites
(OR = 2.14, 95% CI = 1.67–2.74), but not in Mexican
Americans (Table 3). However, compared with nondiabetic
subjects, the average level of DBP was 5.19 mm Hg (95%
CI = −7.35 to −3.03) lower in Mexican Americans with DM
and 2.42 mm Hg (95% CI = −4.37 to −0.46) lower in nonHispanic whites with DM.
Relative ORs of uncontrolled BP, isolated uncontrolled
SBP, and isolated uncontrolled DBP and effect differences
in continuous SBP and DBP were calculated to evaluate
differences in the associations of DM with the BP outcomes
over racial groups (see Table 3). From Table 3, we can see
that the associations of DM with uncontrolled BP, isolated
uncontrolled SBP, and continuous SBP and DBP were
significantly lower in Mexican Americans than in nonHispanic whites (Mexican Americans vs. non-Hispanic
whites: relative OR = 0.53, 95% CI = 0.35–0.80 for
uncontrolled BP; relative OR = 0.62, 95% CI = 0.40–0.96 for
isolated uncontrolled SBP; effect difference = −5.28 mm Hg,
95% CI = −9.77 to −0.78 mm Hg for continuous SBP; effect
difference = −3.36 mm Hg, 95% CI = −6.45 to −0.27 mm
Hg for continuous DBP). Moreover, compared with nonHispanic blacks, Mexican Americans had lower associations
of DM with uncontrolled BP (Mexican Americans vs. nonHispanic blacks: relative OR = 0.55, 95% CI = 0.37–0.82) and
lower average DBP (Mexican Americans vs. non-Hispanic
blacks: effect difference = −3.87 mm Hg, 95% CI = −7.36 to
−0.38 mm Hg).
Discussion
This study examined racial differences in the association
of DM with uncontrolled BP and continuous BP among
participants with diagnosed hypertension in NHANES
1999–2008. DM was reported to be significantly associated
with uncontrolled BP, isolated uncontrolled SBP, and
continuous DBP in the combined study population. Separate
analysis revealed that participants with DM were more likely
to have BP uncontrolled in each group of non-Hispanic
blacks, Mexican Americans and non-Hispanic whites.
The results were consistent with findings from previous
studies.12,13 Uncontrolled BP may cause aneurysm, coronary
2.52 (2.40–2.63)
Family poverty income ratio
30.40 (30.14–30.66)*
30.60 (30.39–30.81)
63.69 (60.93–66.45)
19.72 (18.28–21.16)
37.97 (36.51–39.43)
2.89 (2.80–2.97)
54.83 (52.13–57.52)
56.27 (54.69–57.85)
60.54 (59.88–61.20)
6,134
Total
10.20 (8.06–12.34)
97.17 (96.22–98.12)
Currently taking medications
for hypertension, %
93.89 (92.95–94.82)*
2.51 (1.94–3.08)*
12.86 (11.75–13.98)*
NA
95.19 (94.34–96.04)
7.42 (5.91–8.93)
20.13 (18.06–22.21)
38.03 (35.29–40.78)
50.19 (46.80–53.58)
92.65 (90.89–94.40)
7.89 (5.96–9.82)
23.24 (20.04–26.45)
41.68 (38.40–44.96)
49.03 (45.59–52.46)
94.63 (93.76–95.49)
3.60 (2.89–4.31)*
14.94 (13.85–16.04)*
21.51 (19.69–23.32)*
49.77 (47.47–52.07)
94.60 (93.90–95.30)
4.35 (3.71–4.99)
16.09 (15.07–17.10)
24.49 (22.94–26.04)
49.69 (47.74–51.65)
Data were age adjusted by direct standardization to the diagnosed hypertensive population in National Health and Nutrition Examination Survey (NHANES) 1999–2008 except for agespecific estimates.
*P < 0.001, **P < 0.01 for overall differences of means or percentages of characteristics across diabetes or racial group.
26.29 (24.06–28.53)
Macroalbuminuria, %
NA
Microalbuminuria, %
Albuminuria
Diabetes
52.97 (50.81–55.12)*
39.66 (36.36–42.97)
30.73 (30.33–31.13)
65.65 (62.49–68.81)*
19.11 (17.41–20.82)
39.79 (37.98–41.61)*
3.04 (2.93–3.14)*
51.79 (48.38–55.21)*
54.85 (53.06–56.64)*
61.57 (60.76–62.37)*
3,416
Non-Hispanic whites
194.04 (190.69–197.39) 204.99 (203.25–206.73)** 203.20 (199.75–206,64) 200.66 (197.42–203.90) 202.29 (200.30–204.28) 202.24 (200.55–203.93)
31.70 (31.36–32.05)
60.31 (55.88–64.74)
17.18 (15.20–19.16)
31.66 (28.26–35.06)
2.09 (1.89–2.29)
78.51 (75.46–81.57)
55.98 (52.80–59.16)
56.53 (55.13–57.93)
951
Mexicans
High cholesterol, %
29.76 (29.51–30.01)*
33.44 (32.97–33.92)
53.82 (50.07–57.58)
24.79 (22.24–27.34)
29.53 (27.32–31.74)
2.28 (2.15–2.42)
66.19 (62.68–69.70)
63.27 (60.90–65.65)
56.34 (55.41–57.27)
1,767
Non-Hispanic blacks
Mean, mg/dl
Serum cholesterol
Body mass index,
kg/m2
66.29 (63.29–69.29)**
19.61 (17.99–21.24)
37.35 (35.52–39.19)
3.01 (2.92–3.10)*
51.87 (49.15–54.58)*
56.82 (54.82–58.81)
59.84 (59.12–60.57)*
4,155
Nondiabetic
55.96 (52.17–59.75)
19.26 (17.09–21.44)
Current smoking, %
Alcohol use, %
39.08 (36.31–41.86)
Former smoking, %
Smoking
63.40 (59.53–67.28)
High school or below, %
Education
Female, %
55.21 (52.46–57.96)
62.69 (61.74–63.64)
Age, y
Sex
1,753
Diabetic
Count
Characteristics
Mean or percentage (95% confidence interval)
Table 1. Age-adjusted characteristics of subjects with diagnosed hypertension by diabetes and race in NHANES 1999–2008
Diabetes and Hypertension Control
American Journal of Hypertension 26(11) November 2013 1331
Liu and Song
Table 2. Adjusted odds ratios of uncontrolled blood pressure and regression coefficients on blood pressure for diabetes by race in
diagnosed hypertensive subjects in NHANES 1999–2008
Odds ratios or regression coefficients (95% confidence intervals)
BP outcomes
Non-Hispanic blacks
Mexican Americans
Non-Hispanic whites
(n = 1,767)
(n = 951)
(n = 3,416)
All (n = 6,134)
Adjusted odds ratios of uncontrolled BP
Uncontrolled BP, yes vs. no
2.38 (1.77–3.18)*
1.60 (1.01–2.52)***
2.61 (2.02–3.38)*
2.55 (2.09–3.10)*
Isolated uncontrolled SBP, yes vs. no
1.90 (1.27–2.83)**
1.53 (0.91–2.58)
2.14 (1.67–2.74)*
2.10 (1.71–2.57)*
Isolated uncontrolled DBP, yes vs. no
1.93 (0.93–4.00)
2.48 (0.99–6.22)
1.88 (0.78–4.52)
1.87 (0.98–3.55)
0.12 (−2.34 to 2.57)
0.09 (−1.72 to 1.90)
Regression coefficients on continuous BP
Continuous SBP, mm Hg
−0.62 (−3.98 to 2.73) −4.42 (−9.24 to 0.40)
Continuous DBP, mm Hg
−2.16 (−4.62 to 0.29) −5.19 (−7.35 to −3.03)* −2.42 (−4.37 to −0.46)*** −2.40 (−3.84 to −0.96)**
Data were adjusted for survey cycle, age, sex, education, family poverty income ratio, smoking status, alcohol use, body mass index, serum
cholesterol, albuminuria.
Abbreviations: BP, blood pressure; DBP, diastolic blood pressure; NHANES, National Health and Nutrition Examination Survey; SBP, systolic
blood pressure.
*P < 0.001, **P < 0.01, ***P < 0.05 for the risks of uncontrolled BP, SBP, and DBP and regression coefficients on continuous SBP and DBP
associated with diabetes mellitus by race.
Table 3. Relative odds ratios of uncontrolled blood pressure and effect differences in continuous blood pressure for diabetes between racial
groups of diagnosed hypertensive subjects in NHANES 1999–2008
Relative odds ratios or effect differences (95% confidence intervals)
BP outcomes
Non-Hispanic blacks vs.
Mexican Americans vs.
Mexican Americans vs.
Non-Hispanic whites
Non-Hispanic whites
Non-Hispanic blacks
Relative odds ratios of uncontrolled BP
Uncontrolled BP, yes vs. no
0.96 (0.69–1.34)a
0.53 (0.35–0.80)*
0.55 (0.37–0.82)*
Isolated uncontrolled SBP, yes vs. no
0.85 (0.58–1.24)
0.62 (0.40–0.96)**
0.72 (0.44–1.18)
Isolated uncontrolled DBP, yes vs. no
1.05 (0.37–3.00)
0.46 (0.14–1.53)
0.42 (0.10–1.68)
Effect differences in continuous BP
Continuous SBP, mm Hg
−1.89 (−5.50 to 1.72)
−5.28 (−9.77 to −0.78)**
−4.00 (−8.65 to 0.66)
Continuous DBP, mm Hg
0.51 (−2.44 to 3.45)
−3.36 (−6.45 to −0.27)**
−3.87 (−7.36 to −0.38)**
Data were adjusted for survey cycle, age, sex, education, family poverty income ratio, smoking status, alcohol use, body mass index, serum
cholesterol, albuminuria.
Abbreviations: BP, blood pressure; DBP, diastolic blood pressure; NHANES, National Health and Nutrition Examination Survey; SBP, systolic
blood pressure.
aThe estimate was calculated by the odds ratio of uncontrolled BP for diabetes vs. nondiabetes in non-Hispanic blacks, divided by the corresponding odds ratio of uncontrolled BP for diabetes vs. nondiabetes in non-Hispanic whites.
*P < 0.01, **P < 0.05 for the relative risks of uncontrolled BP, SBP, and DBP and the differences in effects on continuous SBP and DBP for
diabetes mellitus between racial groups.
heart disease, kidney failure, and other life-threatening
complications,24,25 and high SBP is a major health threat,
especially for older Americans.25,26 The role of DM in
uncontrolled BP and high SBP among hypertensive patients
may be anticipated by the following observations. Diabetic
vascular dysfunction predisposes this patient population to
atherosclerosis (narrowing and hardening of the arteries),
which raises the likelihood of having uncontrolled high BP
and increase the risks of adverse cardiovascular events if not
treated.27
Although DM was significantly associated with uncontrolled hypertension in each racial group, the associations
1332 American Journal of Hypertension 26(11) November 2013
were stronger in non-Hispanic blacks and whites than in
Mexican Americans. Mexican Americans were 1.6–1.7 times
more likely to develop DM than non-Hispanic whites.23
Among participants with diagnosed hypertension in our
study, the prevalence of DM in Mexican Americans was
almost 2 times that in non-Hispanic whites. However, a
previous study reported that Mexican Americans with DM
were more likely to be both diagnosed and treated than
non-Hispanic whites.23 We observed that the rates of taking diabetic pills to lower levels of blood sugar were higher
in diabetic Mexican Americans (70.27%) than in diabetic
non-Hispanic blacks and whites (64.23% and 57.07%,
Diabetes and Hypertension Control
respectively), whereas use of antihypertensive medications
is similar in the three racial groups (92.65% in Mexican
Americans, 95.19% in non-Hispanic blacks, and 94.63%
in non-Hispanic whites). These results may partly explain
the observation that despite the higher prevalence of DM
in Mexican Americans, the association of DM with uncontrolled BP in Mexican Americans was not as strong as in
non-Hispanic blacks and whites. The higher associations
of DM with uncontrolled BP in non-Hispanic blacks and
whites revealed that more aggressive treatments for DM and
high BP needed to be considered to weaken the associations
between DM and uncontrolled BP to further reduce high BP
in both groups of hypertensives with DM.
DM is significantly associated with isolated uncontrolled
SBP in non-Hispanic blacks and non-Hispanic whites, but
not in Mexican Americans. Isolated systolic hypertension
is the most common form of high BP for middle-aged and
elderly Americans.28 If left uncontrolled, isolated systolic
hypertension can lead to congestive heart failure, stroke,
or heart attack.26,28–30 The finding from our study that DM
was more associated with isolated uncontrolled SBP in nonHispanic blacks and whites than in Mexican Americans provides evidence that physicians/health-care workers should
be aware of different criteria for targeted SBP control and
more aggressive treatment may be used for patients with
DM to reduce the risks of adverse outcomes associated with
high SBP among white and black individuals with diagnosed
hypertension.
DM was significantly associated with lower average
DBP among diagnosed hypertensive subjects in Mexican
Americans and non-Hispanic whites, as well as the combined population. The result confirmed the indication from
a previous study that DBP was lower in diabetic hypertensive persons than in nondiabetic hypertensive persons.31
This paradox may be attributed to profound effects of DM
on the arterial stiffness in hypertensive patients. A previous
study has shown that DM increases the risk of irreversible
arterial stiffness and hypertension and DM together have
synergistic effects on the development of arterial stiffness.32
When arterial stiffness occurs, the cushioning function of
arteries is impaired, leading to a lower DBP. Another study
has reported that low socioeconomic status may contribute
to greater arterial stiffness.33 In our study, the association
of DM with lower average DBP was stronger in Mexican
Americans than in non-Hispanic blacks and whites. A possible pathway to explain this is that the lower socioeconomic
status in Mexican Americans may induce more severe arterial stiffness associated with DM, which in turn leads to
the further abnormally lower DBP in the diabetic Mexican
Americans.
There were several limitations in this study. First, there
was no detailed drug information for hypertension in the
NHANES survey. Even though we controlled for the confounding impact of taking medications for hypertension,
we could not obtain information for the duration of hypertension and treatment and type and dose of the drug use,
and these factors could influence our results. Second, there
was no assurance that all physicians were aware of the recommended guidelines for hypertension control in diabetic
patients (130/80 mm Hg) during the survey period. This
possibility may confound racial differences in the associations of DM with uncontrolled BP. Finally, diagnosed hypertension in this study was defined based on self-reported
hypertension told by a doctor, average SBP and DBP measurements, and the use of prescribed antihypertensive medications. Our definition of hypertension excluded hypertensive
persons with BP successfully controlled by physical activity,
weight control, and other nonpharmacological techniques.
In summary, although the prevalence of DM was significantly higher in non-Hispanic blacks and Mexican
Americans than in non-Hispanic whites, the association of
DM with uncontrolled BP outcomes was similar between
non-Hispanic blacks and whites and was lower in Mexican
Americans than in non-Hispanic whites. Because non-Hispanic whites account for the majority of the hypertensive
population in the United States, the stronger association of
DM with BP outcomes in non-Hispanic whites compared
with Mexican Americans reveals that in clinics, health providers need more efforts to weaken the association of DM
with uncontrolled BP outcomes by further improving care
for DM and BP in non-Hispanic whites while maintaining
quality work in non-Hispanic blacks and Mexican Americans
to significantly lower the rates of uncontrolled hyper­tension
and reduce the risk of adverse cardiovascular and renal
outcomes in patients with diagnosed hypertension.
ACKNOWLEDGMENT
We are grateful to Dr Kem in Department of Internal
Medicine, the University of Oklahoma Health Sciences
Center for his helpful review and insightful discussion.
This work was supported in part by grant 11SDG5560036
from the American Heart Association and grant HR12-061
from Oklahoma Center for the Advancement of Science and
Technology.
DISCLOSURE
The authors declared no conflicts of interest.
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