The Turkish Journal of Pediatrics
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Hypertension in Children (12–14 Years) – A Case–Control Study in Bursa, Turkey
Nalan Akış1, Kayıhan Pala1, Arzu Meriç-Utku1, Seyithan Bingöl1
Emre Sarandöl2, Hamdi Aytekin1
Departments of 1Public Health, and 2Biochemistry, Uludağ University Faculty of Medicine, Bursa, Turkey
|The aim of this study was to determine the cardiovascular disease risk factors
(risk of overweight/overweight, dyslipidemia, paraoxonase-1 activity, positive
family history, physical inactivity, smoking) that accompany hypertension
and investigate the relationship between hypertension and some of these
This study included 118 hypertensives and 118 age- and sex-matched nonhypertensive
controls aged 12-14 years.
Among controls, 64.4% had no risk factor. Among cases, 34.8% had no risk
factor other than hypertension, and 65.2% had two or more risk factors.
The adjusted odds ratio (OR) (95% confidence interval [CI]) of hypertension
was 5.65 (2.88–11.09) for risk of overweight/overweight. Body mass
index, paraoxonase and arylesterase activities were significantly higher in
hypertensives than those of the control group.
We conclude that it would be useful to routinely evaluate blood pressure and
body weight at schools and, additionally, considering that hypertension alone
is encountered rarely, it would be appropriate to examine the hypertensive
students for other risk factors.
hypertension, overweight, dyslipidemia, paraoxonase-1 activity, children.
|Hypertension is defined as a risk factor for
cardiovascular diseases (CVD) in both adults
and children. The risk of CVD is related to
increment in blood pressure (BP) and presence
of other CVD risk factors. Other cardiovascular
risk factors, such as dyslipidemia, high blood
glucose and obesity, usually accompany
hypertension, and prospective and retrospective
studies reveal that CVD risk factors are rooted
The association between obesity and hypertension
is well known. Physiopathological
mechanisms of hypertension in obesity are
complex, multifactorial and unclear. Many
human and animal studies revealed that the
interaction between hypertension and obesity
is the retention that might be related to
insulin resistance, anatomical changes in the
kidneys, disturbances in vascular functions and
sympathetic nerve system, activation of the
renin-angiotensin system, and changes at the
hypothalamo–hypophyseal–adrenal axis. The
nature of interaction between hypertension
and dyslipidemia is unclear. The combination
of obesity, high BP and dyslipidemia makes
an additional contribution to atherosclerotic
lesions in adolescents.
In recent years, besides the known risk factors
for CVD, studies have been conducted to
investigate paraoxonase-1 (PON-1) activity. It is
claimed that PON-1 activity is related to CVD.
PON-1 is reported to have a protective role in
the atherosclerotic process, by contributing to
the protective effect of high density lipoprotein
(HDL) and preventing the oxidation of low
density lipoprotein (LDL) cholestero. PON-
1 activity varies among healthy individuals.
PON-1 exhibits two common polymorphisms
at amino acids 55 (leucine–methionine change)
and 192 (glutamine–arginine change). Leucine
(L) at position 55 and arginine (R) at position
192 have been associated with increased
cardiovascular risk,. The mechanism by
which these PON-1 polymorphisms increase
susceptibility to CVD is unclear. Both
polymorphisms give rise to different enzyme
activities toward paraoxon, with 192R and
55L alleles being associated with high PON-
1 activity,. The 192 polymorphism results
in two different isoforms that have high
(B) and low (A) activity towards paraoxon.
The population can be subdivided into three
phenotypes: AA (low activity), AB (intermediate
activity) and BB (high activity),. The effect
of the 192 polymorphism is not altered toward
phenylacetate (arylesterase activity). The use
of phenylacetate as substrate is therefore
considered as an index of PON-1 mass.
The prevalence of hypertension shows an
increasing trend among children and adolescents.
Awareness of CVD risk factors that
accompany hypertension is necessary for
The aim of this study was to determine the
CVD risk factors (risk of overweight/overweight,
dyslipidemia, PON-1 activity, positive family
history, physical inactivity, smoking) that
accompany hypertension and investigate the
relationship between hypertension and some
of these risk factors on middle school students
aged 12-14 years.
|Case Presentation |
|The cases in this study were found in a crosssectional
study conducted among middle school
students aged 12–14 years, aiming to determine
hypertension prevalence among them.
This former cross-sectional study was conducted
among 12–14-year-old schoolchildren at Bursa
provincial center between February and June
2006. This study was conducted at 16 middle
schools with 2,478 students. Schools and
students were chosen using stratified random
A questionnaire, including information about
age, sex, family history of CVD, physical
activity, and smoking status, was applied. The
children who smoked at least one cigarette per
week were considered to be at risk of CVD.
To encourage truthful answers, children were
reassured that parents and teachers would not
receive the information about their smoking
status. One of the questions was asked to
evaluate the students’ leisure-time physical
activity patterns. State of physical activity
was determined using the questions used
for adults in various Scandinavian studies
and modified by Ucar et al. for the Turkish
population,. Students were classified into
three physical activity groups according to their
answers: (1) Sedentary activity: students who
ride to school, by vehicle, and do activities
that do not require physical effort, such
as watching television, reading a book; (2)
Moderate activity: students who walk or ride
a bicycle to school and do moderate physical
activities; (3) Active: students who do regular
training in school sports teams, and do heavy
A team consisting of three doctors and one
health officer went to schools in the morning. An
Omron 705 IT automatic sphygmomanometer
was used to measure BP. The cuff size was
approximately 140x480 mm. BP of students was
measured from the right arm at heart level three
times with a minimum of five-minute breaks
after allowing them to rest. Average systolic
and diastolic blood pressures (SBP/DBP) were
calculated and recorded. The evaluation was
undertaken according to the report published
by the American Pediatrics Academy ‘National
High Pressure Education Program Working
Group on High Blood Pressure in Children and
Adolescents’ and ‘The Fourth Report on the
Diagnosis, Evaluation and Treatment of High
Blood Pressure in Children and Adolescents’.
According to age, gender and height, SBP
and/or DBP under 90th percentile was defined
as normal, between 90–95th percentile as prehypertension,
between 95th and 99th percentile
as hypertension, and greater than 99th percentile
as malignant hypertension. BPs of students in
the hypertension and malignant hypertension
groups were measured after two weeks with
the same method and average SBP and DBP
were calculated. The second measurement was
applied to all students who were diagnosed
with hypertension and malignant hypertension
on the first measurement. According to those
measurements, SBP and/or DBP between
95th and 99th percentile was accepted as
hypertension and greater than 99th percentile
as malignant hypertension. Those averages
were taken into account while calculating
hypertension and malignant hypertension
prevalence. Weight of students was measured
sensitive to 0.1 kg after removing shoes and
school uniforms, and height sensitive to
0.1 cm with a height-weight measurer. Body
mass index (BMI) was calculated by using
weight (kg)/height2 (m). Evaluation of BMIs
was undertaken according to the percentage
tables and graphs published in 2000 by the
American Centers for Disease Prevention and
Control (CDC): BMI <85th percentile: normal,
85–94th percentile: risk of overweight, and
≥95th percentile: overweight.
At the end of this study, 147 hypertensive
cases were found. The cases and the parents
of these cases were informed about the case–
control study. The study was conducted on
118 (80.3%) cases because 29 families did
not give their permission for the blood test.
As a control group, 118 students with normal
BP who attended the same school and were
matched for age and sex were selected by a
random sample method.
The study was explained to the students and
written permission was obtained from the
parents and children.
Approximately 5 ml venous blood samples were
obtained from the antecubital veins of students
after 12–14 h fasting. Serum triglyceride (TG),
total cholesterol (TC) and HDL-cholesterol
(HDL-C) were measured the same day that
the blood was collected. Serum aliquots for
PON measurements were kept at -80°C and
analyzed within two months.
Serum levels of TC, HDL-C and TG were
determined using enzymatic assays on an
Aeroset autoanalyzer (Abbott Laboratories;
Irving, TX, USA). LDL-cholesterol (LDL-C)
concentrations were calculated according to
Paraoxonase activity was determined as described
by Eckerson et al.. The rate of hydrolysis of
paraoxon was measured by monitoring the
increase in absorbance at 412 nm at 25°C in the
absence (basal activity) and presence of 1 M NaCl
(salt-stimulated activity) for three minutes. The
basal assay mixture included 1.0 mM paraoxon
and 1.0 mM calcium chloride in 0.05 M glycinenatrium
hydroxide buffer, pH 10.5. The amount of
p-nitrophenol generated was calculated from the
molar extinction coefficient at pH 10.5, which was
18 290 M-1 cm-1. PON activity is expressed in
U/L serum. One unit of PON activity is defined
as 1 μmol p-nitrophenol generated per minute
under the above conditions.
Arylesterase activity was determined by using
phenylacetate as the substrate. The reaction
mixture (incubated for 1 minute at 25°C)
contained 1.0 mM phenylacetate and 0.9 mM
calcium chloride in 9.0 mM Tris-HCl buffer, pH
8.0. Enzymatic activity was calculated from the
molar extinction coefficient 1 310 M-1 cm-1. One
unit of arylesterase activity is defined as 1 μmol
phenol generated per minute under the above
conditions and expressed as kU/L serum.
The phenotype distribution of PON was
determined by the double substrate method,
which calculates the ratio of salt-stimulated
PON activity and arylesterase activity13. The
distribution of the ratio of salt-stimulated PON
activity and arylesterase activity is trimodal, and
a tentative assignment of individuals within
three possible phenotypes was made by dividing
the population at antimodes (2.0 and 7.6).
Our within-run precision (n=20) and betweenrun
precision (n=40) values were below
10% for basal- and salt-stimulated PON and
arylesterase activities in this study.
High levels of TC and LDL-C were defined
as those >200 mg/dl and ≥130 mg/dl,
respectively. TG level ≥130 mg/dl was
considered high25 and HDL-C level <35 mg/dl
was considered low.
All of the statistical analyses were carried
out using SPSS v11.0 for Windows statistical
package (SPSS Inc.; Chicago, IL, USA). In this
study, all quantitative variables are expressed
as mean (standard deviation) or median
(interquartile range, 25–75th percentiles) and
qualitative variables are all expressed in terms
of frequency and percentage (n, %). After
the assessment of normality assumption,
Student’s t-test and when necessary Mann–
Whitney U test were used for the comparison
of the means between the normotensive and
hypertensive groups. The Pearson’s chi-square
test was employed to make comparisons of
categorical variables between the groups. The
determination of the association between
HT and CVD risk factors was estimated
by multivariate logistic regression analysis
(Forward LR) with hierarchical models. All
statistical analysis was applied according to
two-sided hypothesis tests, and a p value of
less than 0.05 was regarded as statistically
|Material and Methods |
|This case–control study was conducted between
1 April and 31 May 2006 and was approved by
the Ethics Committee of the Uludağ University
Medical Faculty (2006-5/29).|
|A total of 236 subjects were included in
the study: 118 hypertensives and 118 nonhypertensive
controls. There were 42 (35.6%)
boys and 76 (64.4%) girls in each group.
The average SBP was 132.1 ± 8.4 mmHg
in hypertensives and 111.6 ± 8.0 mmHg in
normotensives (p<0.001; mean difference:
20.5 [95% confidence interval (CI) 18.3–
22.5]). The average DBP was 76.8 ± 6.8 mmHg
for hypertensives and 66.4 ± 6.3 mmHg for
normotensives (p<0.001; mean difference: 10.3
[95% CI 8.6–12.3]).
Body mass index, basal PON-1 and arylesterase
activities were significantly higher in hypertensives
than in the control group (Table I). From the
perspective of categorical variables, some of the
cardiovascular risk factors were significantly
higher among the cases. Risk of overweight/
overweight was more frequently found in
cases (45.7%) than in controls (12.7%). In
the hypertensives, overweight was the most
frequent risk factor (21.2%) followed by high
Two of the hypertensive students were smokers.
There were no smokers in the control group.
Table II presents the prevalence of combinations
of the risk factors in cases and controls.
Hypertension was included as a cardiovascular
risk factor in the analysis for cases and controls.
Among controls, 64.4% had no risk factor.
Among cases, 34.8% had no risk factor other
than hypertension and 65.2% had two or
more risk factors. The proportion of subjects
| ||Table I. Clinical and Biological Data in Normotensive and Hypertensive Subjects|
| ||Table II. Prevalence of Other CVD Risk Factors* in Hypertensive and Normotensive Subjects|
with multiple risk factors (≥2) was higher
in hypertensives than in controls (65.2% vs.
If hypertension was not taken into account,
prevalence of the subjects having at least
one of the risk factors was still higher in the
hypertensives than in the normotensive controls
(65.2% vs. 35.6%, p=0.001).
Phenotype distributions of PON-1 in normotensive
and hypertensive children are shown
in Figure 1. Of the hypertensives, 52.5% were
low activity phenotype, 39.8% were medium
activity phenotype and 7.7% were high activity
phenotype. These values were 55.6%, 40.2%
and 4.2%, respectively, in the control group.
There was no significant difference in the
phenotype distributions of PON-1 between
cases and controls (p>0.05).
| ||Fig. 1. The phenotypic distribution of the hypertension
and normotensive groups [AA (low activity),
AB (medium activity), BB (high activity)].|
Table III presents the odds ratios (ORs) of
hypertension in logistic regression. The
outcome variable was the presence or absence
of hypertension. In the univariate analysis, the
variables significantly associated with high BP were
PON-1 and risk of overweight/overweight.
After including all the variables of univariate
analysis in the multivariate logistic regression
analysis, the adjusted OR (95% CI) of risk of
overweight/overweight for hypertension was
|We found a significant relation between hypertension
and risk of overweight/overweight. The
ratio of the non-hypertensives who had no
other risk factor was only 34.8%. The rest of
the cases had one or more accompanying risk
factors. The ratio of the cases with two or more
cardiovascular risk factors was significantly higher
in hypertensives compared to normotensives.
There are epidemiological studies that indicate
obesity in children and adolescents as an
important risk factor for hypertension, and some
authors showed a positive association between
BMI and BP,. Among obese/overweight
children, hypertension prevalence is significantly
higher than in children and adolescents with
normal weight,. In the FRICELA study6, it was
indicated that hypertension risk in adolescents
with BMI between 25 kg/m2 and 30 kg/m2 is
2.9 times higher compared to adolescents with
BMI <25 kg/m2. The risk is 4.9 times higher for
those with BMI >30 kg/m2 compared to those
with BMI <25 kg/m2. The multivariate OR of
hypertension for risk of overweight/overweight
was 5.65, the highest, in our study.
Previous studies have also shown that, in addition
to the risk of hypertension, obesity further
enhances total cardiovascular risk by increasing
LDL-C levels, reducing HDL-C levels, diminishing
glucose tolerance, and predisposing to the
development of left ventricular hypertrophy,.
In our study, dyslipidemia prevalence, though
not significant, was higher in hypertensives
compared to normotensives.
| ||Table III. Logistic Regression Analysis (Crude and Adjusted ORs of Hypertension)|
Serum PON activity was found to be significantly
higher in hypertensives compared to
normotensives in our study. A significant relation
between PON-1 activity and hypertension was
also observed in univariate analysis. However, the
significance vanished after multivariate logistic
regression analysis. Phenotype distribution was
not significantly different between cases and
controls. There are limited data on serum PON
activity in patients with hypertension, and there
is only one recent study that investigated serum
PON activity in hypertensive adolescents.
In that study, compared with the controls,
the investigators did not find any significant
difference in the enzyme activity in adolescent
patients with essential or obesity-induced
hypertension. In line with our findings, those
authors did not find any significant difference
in the phenotype distributions between the
hypertensive and control groups. However,
in a study that was carried out with adult
hypertensive patients, Uzun et al.31 reported
decreased serum PON-1 activity in white-coat
and sustained hypertension. Those authors
also found increased plasma malondialdehyde
(MDA) levels, an indicator of oxidative stress,
and suggested that decreased serum PON-1
activity might be a contributing factor and/
or a result of increased oxidative stress in
hypertensive subjects, since lipid peroxidation
products are both substrates and inhibitors of
PON-131. However, Barath et al. did not find
any difference in plasma MDA levels between
the patients with essential or obesity-induced
hypertension and the control group. We cannot
find an explanation for the increased serum PON
activity in hypertensive adolescents observed
of the present study is the lack of oxidative
stress parameters. Furthermore, there might be
several factors contributing to the discrepancies
between the studies, such as age, diet, smoking,
and exercise, etc.
In our study, the CVD risk factor rate was higher
among hypertensives. The percentage of cases
who had only hypertension was 34.7%. One or
more of the risk factors such as dyslipidemia,
positive family history, physical inactivity, and
risk of overweight/overweight accompanied
hypertension in the other cases. In parallel
with our findings, Foucan and colleagues3
reported that other CVD risk factors were more
often observed in hypertensives compared to
normotensives, and furthermore, the results did
not change when hypertension was excluded.
In conclusion, the fact that we did not
differentiate between primary and secondary
hypertension can be considered a limitation
of the study. Nevertheless, CVD risk factors
were observed at a higher rate in hypertensives
compared to normotensives. In particular, risk
of overweight/overweight is the most important
risk factor in hypertensives. BP and weight
measurements should be routinely conducted in
schools. We conclude that it would be useful
to routinely evaluate blood pressure and body
weight in schools and, additionally, considering
that hypertension is rarely encountered alone, it
would be appropriate to evaluate the hypertensive
students for other risk factors.
This study was supported by a grant from the
Research Fund of Uludağ University (Project
We thank Dr. Semra Akgöz, Lecturer at
Uludağ University Medical Faculty, Biostatistics
Department, for conducting the statistical
analysis of this study.
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