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126
PREV ALENCE OF CORONARY ARTERY
DISEASE RISK FACTORS IN SAUDI CHILDREN
HAZZAA M. AL-HAzzAA, PhD; MOHAMMED A. SULAIMAN, MD; KHALID F.
AL-MoBAIREEK, MD; OMAR S. AL-ATIAS, PhD
Two hundred and twenty boys, 7 to 12 years of age, were subjected to a comprehensive medical,
anthropometric, and physiological evaluation to assess the prevalence of coronary artery disease
risk factors. These risk factors include obesity, blood lipids and lipoproteins, blood glucose, blood
pressure, cardiorespiratory fitness, and physical activity level. The results of this study indicate that
there are no significant age-related differences in total cholesterol, triglycerides, LDL-cholesterol,
HDL-C/cholesterol ratio, or blood glucose. No significant hypertension was detected among the
subjects. Using relative body fat, 15.6% of the boys were considered obese. Body fat percent
showed significant inverse relationships with cardiorespiratory fitness, HDL-cholesterol, HDLC/cholesterol ratio, and was related positively to systolic and diastolic blood pressures but not to
total cholesterol. Blood pressure was not related to cholesterol or triglyceride levels. The findings
of this study also showed that 22.9% ofthe boys exceeded cholesterollevel of 5.2 mmol/L, 26.4 %
had triglyceride level above 1.4 mmol/L, 15.4% had a LDL-cholesterollevel above 3.4 mmol/L,
and 4.0% had HDL-cholesterol below .96 mmol/L. We conclude that a considerable percentage of
the tested schoolchildren between the ages of 7 and 12 years have one or more coronary artery
disease risk factors.
ALTHOUGH ATHEROSCLEROSIS and coronary
artery disease (CAD) manifestations do not usually
appear until later adult life, they seem to have their
origins in children.l-4 Data from the Bogalusa Heart
Study indicate that the atherosclerotic process may
begin as early as the first decade of life.5
Furthermore, epidemiological studies of CAD risk
factors in children have reported the existence of one
or more risk factors including hyperlipidemia,
cigarette smoking, inadequate physical activity, and
obesity.6-l0 Children who are obese and have high
levels of blood pressure and abnormal lipid
From the Exercise Physiology Laboratory, Department of Physical
Education (Drs. AI-Hazzaa and Sulaiman), College of Education,
Department of Pediatrics (Dr. AI-Mobaireek), College of
Medicine, and Department of Biochemistry (Dr. AI-Attas),
College of Science, King Saud University, Riyadh, Saudi Arabia.
Address reprint requests and correspondence to Dr. AIHazzaa:
Exercise Physiology Laboratory, Department of Physical
Education, College of Education, P.O. Box 2458, Riyadh 11451,
Saudi Arabia.
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
profiles are likely to exhibit these CAD risk factors as
they grow older .1,4,11,12 Consequently, prevention
and modification of these risk factors have become
the focus of many primary prevention programs
targeted at school-age children.9,13,14
Data on the distribution of CAD risk factor
variables in Saudi children are, undoubtly, lacking.
Therefore, it was the purpose of this study to examine
the prevalence of CAD risk factor variables in a
group of preadolescent Saudi boys.
Materials and Methods
Subjects
Invitations to participate in this study,
accompanied by a complete description of the
procedures, were sent to the parents of each boy in
the second to sixth grades at a nearby primary school
in the city of Riyadh. The children in the school are
considered to come from working, predominantly
middle-class families. Of the 320
CAD RISK FACTORS
boys who received invitation letters, 220 agreed to
participate in the study and gave informed consent.
Each participant underwent a complete physical
examination. Eight boys were considered
adolescents or postadolescents and therefore were
not included in the analysis. The remaining 212 boys
were considered Tanner Stage 115 and were
included in this study. The project was approved by
the Educational Research Center of King Saud
University.
Anthropometry
Body weight (kg) and height (em) were measured
using a precalibrated portable scale and a height
measuring rod, respectively. Measurements of the
chest, triceps, and subscapular skin-folds were taken
on the right side, using a Harpenden caliper
according to standard procedures. 16 Body fat
percent was then calculated from skinfold
measurements utilizing a recent regression equation
developed for children.17.18 Skeletal growth was
assessed from the width measurements of the
shoulder, hip, knee, and wrist. Muscular
development was assessed from the circumference
measurements of the upper arm, mid-thigh, and calf
according to standard procedures. 16 In addition,
blood pressure measurements were performed by a
trained physician on the right arm at the level of the
heart while the subject was seated, using a mercury
sphygmomanometer with cuff size appropriate for
upper arm length and circumference. The first
(systolic) and fourth (diastolic) Korotkoffs sounds
were recorded.
Blood Analysis
Within 2 hours following a 12-hour fast, a 5 mL
blood sample was drawn from the antecubital vein
using a butterfly needle. No more than two attempts
to get blood samples were performed on any child.
Blood samples were then coded and rapidly
transported to the laboratory where centrifuging took
place. The serum was transferred into another tube
and was stored in -lOoC until time of analysis. Blood
glucose was analyzed using a glucose analyzer II
(Beckman Instruments, Inc., Brea, California, USA).
Enzymatic colorimetric method was used in the
determination of triglycerides, total cholesterol, and
HDL-cholesterol using a commercially available kit
(Boehringer
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
127
Mannheim GmbH, Diagnostica, Germany). LDLcholesterol was determined using the Friedewald
formula.19 The quality control of the laboratory
measurements, where blood analysis was performed,
was routinely checked.
Daily Physical Activity
Daily physical activity was assessed for each
subject using heart rate telemetry (Vantage XL, Polar
Electronics). The heart rate monitor was attached on
each boy for 8 hours after the school day. Disposable
electrodes were used instead of the original belt that
was supplied by the manufacturer. This device has
been found to be very reliable and valid for recording
heart rates in adults20 and children.21.22 Heart rates
were retrieved after each test and the percentages of
time spent at heart rates above specific indices were
calculated. The children were instructed not to
modify their usual daily physical activity patterns
during testing days.
Cardiorespiratory Fitness
Cardiorespiratory fitness was assessed by
measuring the maximal oxygen uptake during
incremental treadmill test. The exercise tests were
conducted 2 hours after a light meal in a comfortable
laboratory temperature. After familiarization and
warm-up periods, the treadmill speed was increased
until the optimal running speed for each individual
was reached which ranged from 7 to 10 kmlh. The
speed was then kept constant but the treadmill
elevation was raised by 2% every 2 minutes until the
child became exhausted. Th~ children were verbally
encouraged to exercise to maximal efforts. A member
of the testing staff was positioned very close to the
exercising subject for the duration of the test.
Expired air was collected and measured, utilizing
an automated open-circuit system with 30-second
sampling intervals (EOS-Sprint Jaeger, Germany).
Gas analyzers were calibrated before each test with a
known mixture of gases. Oxygen uptake was
considered to be maximal when a plateau was
reached. If a plateau was not reached, additional
criteria were used including a maximal heart rate of
above 90% of expected maximal heart rate and a
respiratory-exchange ratio above 1.0 level. In
addition, the heart rate was
128
AL-HAZZAA ET AL
continuously monitored and recorded during the
exercise test using a CM5 lead, utilizing a singlechannel electrocardiogram monitor and recorder
(Helligi, Germany).
Data Analysis
Data were entered into a computer, and descriptive
statistics were obtained for all variables according to
the five age groups utilizing the SPSS program. A
one-way ANOV A with Scheffe's test was used to
determine the differences between age groups in all
variables. Pearson correlation was performed to test
relationships among CAD risk factors, physical
activity, and cardiorespiratory fitness. The level of
significance was set at 0.05 level.
Results
Physical characteristics of the subjects by age
groups are presented in Table 1. The mean values for
weight, height, body mass index (BMI), and body
surface area increased from one age group to the
next. The sum of the chest, triceps, and subscapular
skinfolds, as well as body fat percent were
considerably higher in the older subjects compared to
the younger ones. Mean values of the anthropometric
measurements for the present sample are considered
within 1 SD of the average population values.23
However, more than 15% of the subjects had body fat
contents exceeding 25% of body weight. Table 2
presents some selected CAD risk factor variables
grouped by age. There were no significant age-related
differences in total cholesterol, triglycerides, LDLcholesterol, HDL-C/cholesterol ratio, or blood
glucose. HDLcholesterol decreased slightly within
the last two age groups. There were, however,
consistent and significant increments in the systolic
blood pressure. The diastolic blood pressure showed
a small and insignificant increase across age groups.
The increases in systolic and diastolic blood
pressures from age 7.5 to 11.6 years were 14 and 2.6
mm Hg, respectively. No incidence of significant
hypertension was noted (> 95th percentile24). Values
of maximal oxygen uptake (V02 max mLlkg/min), a
measure of cardiorespiratory fitness, showed no
significant differences across age.
Analysis of heart rate telemetry indicated that
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
the most physically active boys were the 11- and 12year-olds. When compared to the other age groups,
they had &pent the highest percentage of their
monitored time at a heart rate above 159 beats/min.
Only 15% of the total sample of boys spent 20
minutes or more at a heart rate above 159 beats/min.
The correlation matrix of the measured variables is
shown in Table 3. Total cholesterol value had no
association with any of the obesity measures (weight,
BMI, body fat percent), cardiorespiratory fitness, or
physical activity. The level of triglycerides was
significantly related to all measures of obesity as well
as cardiorespiratory fitness. However, when the effect
of body fat percent was controlled, the association
between cardiorespiratory fitness and triglycerides
was no longer significant. HDLcholesterol level
showed significant relationships with all measures of
obesity and with physical activity. Both systolic and
diastolic blood pressures correlated significantly with
body weight, BMI, and body fat percent. The systolic
blood pressure was related to physical activity, while
the diastolic blood pressure was related to both
physical activity and cardiorespiratory fitness. The
cardiorespiratory fitness did not relate to diastolic
blood pressure when the effect of body fat was
removed.
An important question that this study attempts
to address is to what extent are these school boys at
risk of CAD? The 95th percentile of Lipid Research
Clinics Population Studies,25 as recommended by
Kwiterovich,26 was used as cut off values. However,
there are different views regarding the recommended
cut off values for cholesterol. The National Institute
of Health Consensus Statement recommends the 90th
percentile as the cut off value for high risk.27 The
American Academy of Pediatrics recommends a cut
off value corresponding to the 75th percentile.28
Table 4 and Figure 1 indicate the prevalence of
CAD risk factors in the present sample. Using the
95th percentile (5.2 mmollL) as the cut off value for
total cholesterol, 23% of the boys were at risk. This
percentage increased to about 50% when the 75th
percentile (4.6 mmollL) was used as a cut off value.
Regarding the levels oftriglycerides, HDLcholesterol,
and LDL-cholesterol, there were 26.4%,4%, and
15.4% ofthe boys at risk, respect.
Table 1.
Physical characteristics of the subjects by age groups (mean :t SD).
Age groups
Variables
1
2
4
5
All
41
38
212
8.5
3
4
7
9.5
Number of subjects
42
44
Age (y)
7.5
10.5
11.6
9.5
:t .4
:t .3
:t .3
:t .3
:t.4
:t 1.4
24.6cd
27.31g
29.7
35.OC1
39.2dg
31.0
:t 5.6
:t 6.3
:t 5.8
:t 10.9
:t 10.5
:t 9.5
123.oabcd
129.2alg
132.6bhi
137.4chj
142.9dig
133.0
:t 7.2
:t 5.4
:t 5.4
:t 7.4
:t 7.3
:t 9.3
16.1d
16.3g
16.9
18.5
19.1dg
17.3
:t 2.5
:t 2.9
:t 2.9
:t 3.8
:t 3.5
0.92cd
0.99g
1.05i
1.15<
:t .12
:t .12
:t .10
:t .18
22.1d
24.5g
23.9i
32.6
:t 13.7
:t 14.0
:t 14.7
:t 25.2
Body fat ('Yo)
14.Od
15.68
14.9i
18.1
:t 6.6
:t 6.6
:t 8.9
LBM (kg)
:t 6.4
21.1
!>cd
:t 3.3
23.01g
25.3hhi
28.6ctl1
:t 3.6
:t 3.4
:t 4.7
:t 4.4
1.24dg
i
:t .16
38.6dg
i
:t 27.0
21.3dg
i
:t 11.1
30.2dg
i
:t 4.6
Weight (kg)
Height (cm)
BMI (kglm2)
BSA (m2)
SSF(mm)
BMI
1.07
:t .18
28.0
:t 20.2
16.7
:t 8.4
25.6
:t 5.0
= body mass index; BSA = body surface area; SSF = sum of skinfolds (chest, triceps and subscapular); LBM = lean body mass.
Significant difference at 0.05 level:
Table 2.
al *2;
hI *3;
<1 *4;
dl *5;
c2*3;
12*4; g2*5;
h3*4;
i3*5;
j4*5.
Selected coronary artery disease risk factor variables by age groups (mean :t SD).
Age groups
Variables
Age (y)
Total cholesterol
(mmollL)
Triglycerides
(mmollL)
HDL-cholesterol
(mmoI/L)
LD L-cholesterol
(mmollL)
HDL-C/cholesterol
('Yo)
Blood glucose
(mmol/L)
Systolic blood pressure
(mm Hg)
Diastolic blood pressure
(mm Hg)
V02 max'
(mLlkglmin)
Time HR > 159 beats/min
(min)"
Percent of total time
('Yo)
1
2
3
4
5
All
7.5
8.5
9.5
10.5
11.6
9.5
:t.4
:t .3
:t .3
:t .3
:t.4
:t \.4
4.69
:t .73
1.24
:t .56
1.42
:t .36
2.70
:t .74
30.8
:t 8.5
3.74
:t .51
93.6cd
:t 9.8
59.2
:t 7.5
49.1
:t 6.6
8.9
:t 9.6
1.87
:t 2.0
4.75
:t .89
1.19
:t .51
1.45
:t .30
2.73
:t .90
31.5
:t 8.7
3.65
:t .28
99.8g
:t 9.2
58.4
:t 7.5
46.9
:t 5.9
6.8
:t 7.8
1.41
:t 1.6
4.64
:t .97
1.16
:t .45
1.45
:t .30
2.59
:t .87
32.3
:t 8.5
3.75
:t .44
97.4i
:t 10.8
57.8
:t 7.2
47.7
:t 4.8
8.7
:t 8.1
1.81
:t1.7
4.34
:t .79
1.25
:t .68
1.31
:t .25
2.44
:t .75
30.8
:t 7.0
3.49
:t .67
102.7c
:t 10.6
6\.4
:t 7.1
48.9
:t 6.0
7.7
:t 9.6
1.61
:t 2.0
4.76
:t .63
1.18
:t .68
1.32
:t .26
2.88
:t .66
28.2
:t 5.9
3.56
:t .46
107.5dgi
:t 9.6
61.8
:t 6.3
47.8
:t 6.8
15.4
:t 17.3
3.22
:t 3.6
4.63
:t .82
1.20
:t .57
1.39
:t .30
2.66
:t .79
30.8
:t 7.9
3.64
:t .49
99.9
:t 10.9
59.6
:t 7.3
48.4
:t 6.0
9.6
:t 10.5
1.98
:t 2.1
· Maximal oxygen uptake, a measure of cardiorespiratory fitness.
.. Measure of daily physical activity level; HR = heart rate.
Significant difference at 0.05 level:
a1 *2;
b1 *3;
c1 *4;
d1*5;
e2*3;
12*4;
g2*5;
h3*4;
i3*5;
j4*5.
Table 3. Intercorrelations between various anthropometric, physiologic and coronary artery disease risk factors.
Variables
1
2
3
4
5
6
7
8
9
10
11
12
Body weight
Body height
.76"
Body mass index
.91"
.91"
Body fat percent
.83**
.45**
Physical activity.
-.04
.07
V02maxb
-.39** -.12
.87**
-.09
-.12
-.52" -.55'.
.23
Total cholesterol
.01
-.01
.01
.05
Triglycerides
.16'
-.02
.22**
.28** -.20
HD L-cholesterol
-.21" -.15'
LDL-cholesterol
HD L-C/cholesterol
.04
.05
-.20" -.13
.16
-.03
-.37**
.14'
-.20** -.24'.
.29**
.12
.19**
.17'
.01
.05
.07
.04
.87'
-.11
-.18'
-.22**
.09
.11
-.54** -.24**
.69**
.73**
.13
.10
-.06
-.13
-.16'
.06
.11
-.16
.09
-.18'
Systolic blood pressure
.56"
.56"
.46.'
Diastolic blood pressure
.43**
.30**
.41**
.46** -.27'
-.21
.43** -.30" -.29'
-.15'
.62**
· Measured as the percent of time spent at heart rate above 159 beats/min.
b Maximal oxygen uptake (mUkg/min).
, P "" 0.05.
** P "" 0.01.
Table 4. Prevalence of coronary artery disease risk factors in Saudi children.
Risk factors
Criteria
Total cholesterol
;;" 5.2 mmol/La
;;" 4.8 mmollLb
;;" 4.6 mmollLc
No. of subjects above criteria
%
46
22.9
82
40.8
100
49.7
Triglycerides
;;" 1.4 mmollLa
53
26.4
HDL-cholesterol
,,;; .96mmollL.
8
4.0
LDL-cholesterol
;;" 3.4 mmollL.
31
15.4
Systolic blood pressure (mm Hg)
;;" 95th percentiled
0
0
;;" 90th percentiled
9
4.2
;;" 95th percentiled
0
0
Diastolic blood pressure (mm Hg)
;;" 90th percentiled
Body fat percent
V02 max
9
4.2
;;"25%e
33
;;"20%e
45
15.6
21.
2
12.
7
,,;; 42 mL/kg/minf
8
·
95th percentile from Lipid Research Clinics Population Studies Data Book,25 as recommended by Kwiterovich.26
b 90th percentile, as recommended by the National Institute of Health.27
c 75th percentile, as recommended by the American Academy of Pediatrics. 28
d Age adjusted 95th and 90th percentiles from the Report of the Second Task Force on Blood Pressure Control in Children,
1987.24
e Cut off values for the definition of obesity. 17
f Cut off value for cardiorespiratory fitness.29
Journal of the Saudi Heart Association, Vol. 5,
CAD RISK FACfORS
131
30
26.4
25
20
15
10
5
o
TC
TG
HDL
LDL CRF
08
Figure 1. Prevalence of CAD risk factors in Saudi children
(percent of total group above cut off values). TC = total
cholesterol; TG = triglycerides; HDL = HDL-cholesterol; LDL
= LDL-cholesterol; CRF = cardiorespiratory fitness; OB =
obesity.
tively. Utilizing the 95th percentile of the Report of
the Second Task Force on Blood Pressure Control in
Children,24 none of the children was found to be at
risk for systolic and diastolic blood pressures.
However, a total of 9 boys (4.2%) were at risk when
the 90th percentile was used. Analysis of body fat
content revealed that 15.6% of the subjects exceeded
the cut off values for obesity which was set at 25%
of body fat. 17 Finally, the cut off value for
cardiorespiratory fitness was set at < 42
mL/kg/min,29 resulting in 12.7% of the boys below
this cut off value.
Discussion
It must be stated unequivocally that the present
sample was self-selected and thus generalization of
the results concerning CAD risk factors must be
interpreted cautiously. However, it was recognized
from the beginning of the project that in this
multifactorial study, a randomized sample of
schoolchildren in the city of Riyadh was clearly
prohibitive in terms of financial and logistic
perspectives.
The prevalence of obesity in this study was
considerably high. The percentage of boys who had
body fats exceeding 25% of body weight was
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
15.6(%). Obesity is recognized as a predisposing
factor for cardiovascular disease, particularly via its
role in the development of other risk factors.
Gortmaker and co-workers3o estimated the
prevalence of obesity to be at 22.6% for boys between
12 to 17 years. Lohman,17 using 25% fat for boys 6
to 11 years, found that the prevalence of obesity
ranged from 5% to 22%. Furthermore, a number of
studies found that body fat in children and
adolescents is associated with elevated levels of CAD
risk factors.30,3l
Results of V02 values are well within the range of
values reported in the literature.32 Cardiorespiratory
fitness, as measured by V02 max, has been found to
be related to lower CAD risk factors in boys.8,10 In
the present study, the percent of body fat is
significantly related to V02 max. Low levels of
physical activity have been associated with higher
levels of cardiovascular disease risk factors in
adults.33-35 The majority of the schoolchildren in our
sample were not physically active enough to promote
cardiorespiratory fitness.36 About 85% of the sample
in this study could not sustain a daily heart rate level
above 159 beats/min for 20 minutes or longer.
Although comparison of absolute values of
cholesterol between different studies is not without
limitation,37 it is interesting to note that the mean
total cholesterol level reported in this study is similar
to those levels reported for several European and
American children.7,9,3l,38-40 However, the values
of total cholesterol were high when compared to other
studies.6,25,4l Resnicow and co-workers42 reported
mean values for black American children as similar to
ours, but their values for white American children
were higher than the mean values reported in our
study. In contrast to the above-mentioned studies, Tell
and Vellar8 reported higher val'!es of cholesterol than
this study.
A feasible, ideal mean level of total cholesterol of
4.58 mmol/L has been suggested,28 and this is lower
than the mean level observed in this study. In fact,
nearly 50% of the subjects exceeded this level. With
this high mean value in childhood, as seen in this
study, it would be difficult to create an ideal total
cholesterol level in adulthood such as in the third,
fourth, and fifth decade of life. The 50th and 95th
percentile levels for blood cholesterol
132
AL-HAZZAA ET AL
have been found to increase by 0.6, 1.0, and 1.8
mmollL, respectively. 2
Comparison of our cholesterol values with those
reported from 15 countries43 revealed that the
percentage of our subjects above the level of 4.65
mmollL was similar to those percentages reported
from Germany, The Netherlands, Kuwait, and
Norway. However, much lower percentages were
reported by the same study for children from Nigeria
(9%), Italy (10%), Greece (10%), Japan (13%), and
the United States (16%). Furthermore, the percentage
of our boys who exceeded the cut off value of 5.2
mmollL (22.9%) was similar to those percentages
reported previously,?,29,43 But Gilliam et al6
reported that only 10.5% of their sample of active
children had cholesterol values above 5.2 mmollL.
Fasting triglyceride levels were notably high when
compared to other published values for
children.6,8,25,29 Triglyceride levels have been
shown to increase with age to reach a value of 1.20
mmollL by age 18 years.7 Our data did not show
significant differences between age groups. The
percentage of boys in this study who exceeded the cut
off value for triglycerides seems considerably high
when compared to other reported figures.6,7,29
Values for HDL-cholesterol in this study were similar
to other published data for children.8,25,38,39 The
mean values for LDLcholesterol were comparable to
those found in the Lipid Research Clinics Population
Studies.25
The blood pressure level is influenced by various
factors, including the physiological and emotional
state of the child. None of the boys in our sample was
physically active prior to blood pressure
measurement. Blood sampling was performed in a
later visit to the school in order not to influence the
blood pressure measurements. Results of our blood
pressure values were similar to some studies29,38 but
lower than others. 7 ,8,39,41,44
In conclusion, the findings of this study indicate
that a considerable percentage of the tested
schoolchildren, between the ages of 7 and 12
years, exhibited one or more CAD risk factor(s).
Acknowledgments
This study was supported by the Research Center, College
of Education, King Saud University. The
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
assistance of J. Algroni, M. Yosri, S. Tawfeeq, and F.
Rahmi during data collection and A. Elian during
data analysis are acknowledged.
References
1. Kannel W, Dawber T. Atherosclerosis as a pediatric
problem. J Pediatr 1972;80:544-54.
2. Summary and recommendations of the conference on blood
lipid levels in children: optimal levels for early prevention of
coronary artery disease. Prev Med 1983;12:728-40.
3. Velican D, Velican C. Studyoffibrousplaquesoccurring in the
coronary arteries of children. Atherosclerosis 1979;33:20115.
4. Voller R, Strong W. Pediatric aspects of atherosclerosis.
Am Heart J 1981;101(6):815-36.
5. Berenson G, Foster T, Frank G, et al. Cardiovascular
disease risk factor variables at the preschool age: the
Bogalusa Heart Study. Circulation 1978;57:603-12.
6. Gilliam T, Katch V, Thorland W, et al. Prevalence of
coronary heart disease risk factors in active children, 7 to
12 years of age. Med Sci Sports Exerc 1977;9:21-5.
7. Lauer R, Connor W, Leaverton P, et al. Coronary heart
disease risk factors in school children: the Muscatine
Study. J Pediatr 1975;86: 697-706.
8. Tell G, Vellar O. Physical fitness, physical activity, and
cardiovascular disease risk factors in adolescents: the
Oslo Youth Study. Prev Med 1988;17:12-24.
9. Tell G, Tuomilehto J, Epstein F, et al. Studies of
atherosclerosis determinants and precursors during childhood
and adolescence. Bull WHO 1986;64(4):595605.
10. Thorland W, Gilliam T. Comparison of serum lipids between
habitually high and low active pre-adolescent males. Med Sci
Sports Exerc 1981;13:316-21.
11. Webber L, Baugh J, Cresonta J, et al. Transition of
cardiovascular risk factors from adolescence to young
adulthood: the Bogalusa post high school study. Circulation
(suppI2) 1983:111-60.
12. Webber L, Srinivasan S, Wattigney W, et al. Tracking of
serum lipids and lip,oproteins from childhood to adulthood.
Am J Epidemioll991;133(9):884-99.
13. Walter H, Hofman A, Vaughan R, et al. Modification of
risk factors for coronary heart disease. N Engl J Med
1988;318: 1093-100.
14. Williams C, Arnold C, Wynder E. Primary prevention of
chronic disease beginning in childhood: the know your
body program: design of study. Prev Med 1977;6:344-57.
15. Tanner J. Growth at adolescence. Oxford: Blackwell
Scientific Publications, 1962.
16. Lohman T, Roche A, Martorell R. Anthropometric
standarization reference manual. Champaign, Illinois:
Human Kinetics, 1989.
17. Lohman TG. Assessment of body composition in
children. Pediatr Exerc Sci 1989;1:19-30.
18. Slaughter M, Lohman T, Boileau R, et al. Skinfold
equations for estimation of body fatness in children and
youth. Hum Bioi 1988;60(5):709-23.
CAD RISK FACTORS
19. Friedewald W, Levy R, Fredrickson D. Estimation ofthe
concentration of low-density lipoprotein cholesterol in
plasma, without use of the preparative ultracentrifuge. Clin
Chern 1972;18:499-502.
20. Leger L, Thivierge M. Heart rate monitors: validity, stability
and functionality. Physician Sports Med 1988; 16(5): 143-51.
21. Treiber F, Musante L, Hartdagan S, et al. Validation of heart
rate monitor with children in laboratory and field settings.
Med Sci Sports Exerc 1989;21(3):338-42.
22. Tsanakas J, Bannister 0, Boom A, et al. The sports tester, a
device for monitoring the free running test. Arch Dis Child
1986;61:912-4.
23. AI-HazzaaHM. Anthropometric measurements of Saudi
boys aged 6-14 years. Ann Hum Bioi 1990;17(1):33-40.
24. Report of the Second Task Force on Blood Pressure
Control in Children-1987. Pediatrics 1987;79(1):1-25.
25. Lipid Research Clinics Population Studies Data Book.
National Institute of Health: Government Printing
Office; 1980, Publication No. 80-1527.
26. Kwiterovich P. Biochemical, clinical, epidemiologic, genetic,
and pathologic data in pediatric age group relevant to the
cholesterol hypothesis. Pediatrics 1986;78:349-62.
27. Lowering blood cholesterol to prevent heart disease.
JAMA 1985;253:2080-6.
28. American Academy of Pediatrics, Committee on
Nutrition. Indications for cholesterol testing in children.
Pediatrics 1989;83:141-2.
29. Wilmore J, McNamara J. Prevalence of coronary heart
disease risk factors in boys, 8 to 12 years of age. J Pediatr
1974;84(4):527-33.
30. Gortmaker S, Dietz W, Sobol A, et al. Increasing
pediatric obesity in the United States. Am J Dis Child
1987;141:535-40.
31. Williams D, Going S, Lohman T, et al. Body fatness and risk
for elevated blood pressure, total cholesterol, and serum
lipoprotein ratios in children and adolescents. Am J Public
Health 1992;82(3):358-63.
32. Krahenbuhl GS, Skinner JS, Kohrt WM. Developmental
aspects of maximal aerobic power in children. Exerc Sport
Sci Rev 1985;13:503-38.
Journal of the Saudi Heart Association, Vol. 5, No.3, 1993
133
33. American Heart Association Position Statement. Statement on
exercise-benefits and recommendations for physical activity
programs for all Americans. Circulation 1992;86(1):340-4.
34. Paffenbarger R, Hyde R. Exercise in the prevention of
coronary heart disease. Prev Med 1984;13:3-22.
35. Powell K, Thompson P, Casperson C, et al. Physical
activity and the incidence of coronary heart disease.
Annu Rev Public Health 1987;8:281-7.
36. American College of Sports Medicine. Opinion
statement on physical fitness in children and youth. Med
Sci Sports Exerc 1988;20(4)422-3.
37. Blank D, Hoeg J, Kroll M, et al. The method of
determination must be considered in interpreting blood
cholesterol levels. JAMA 1986;25:2867-70.
38. Armstrong N, Balding J, Gentle P, et al. Estimation of
coronary risk factors in British schoolchildren: a
preliminary report. Br J Sports Med 1990;24(1):61-6.
39. Armstrong N, Williams J, Balding P, et al. Cardiopulmonary
fitness, physical activity patterns, and selected coronary risk
factor variables in 11- to 16-yearolds. Pediatr Exerc Sci
1991;3:219-28.
40. Kromhout D, Obermann-De Boer G, Coulander C. Major
CHD risk indicators in Dutch schoolchildren aged 10-14
years: the Zutphen schoolchildren study. Prev Med
1981;10:195-210.
41. Kafatos A, Panagiotakopoulos G, Bastakis N, et al.
Cardiovascular risk factor status of Greek adolescents in
Athens. Prev Med 1981;10:173-86.
42. Resnicow K, Morley-Kotchen J, Wynder E. Plasma cholesterol
levels of 6585 children in the United States: results of the
know your body screening in five states. Pediatrics
1989;84(6):969-76.
43. Wynder E, Williams C, Laakso K, et al. Screening for risk
factors for chronic disease in children from fifteen countries.
Prev Med 1981,10:121-32.
44. Hofman A, Walter H, Connelly P, et al. Blood pressure and
physical fitness in children. Hypertension 1987;9(2):188-91.