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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 3, May/June 2019
AFRICA
143
•
ratio of trunk-to-limb skinfolds (SS/TB)
=
(SSCP
+
SPIL)/
(TRCP
+
BCP)
•
ratio of subscapular-to-triceps skinfolds (S/ST)
=
SSCP/
(SSCP
+
TRCP)
As an indicator of lower trunk fat patterning, the ratio of
subscapular-to-supra-iliac skinfolds was used:
•
trunk ratio (SS/SSTB)
=
(SSCP
+
SPIL)/(SSCP
+
SPIL
+
BCP
+
TCP).
2
An average of two systolic and diastolic blood pressure readings
was taken with an electronic monitoring kit, with the child seated
and resting for at least five minutes. The bladder of the Micronta
device contains an electronic infrasonic transducer that monitors
the pulse rate and blood pressure and displays them concurrently
on the screen. The device is a versatile instrument that has been
designed for research and for clinical purposes. In a pilot study,
conducted before the survey, there was a high correlation (
r
=
0.93) between the readings taken with the automated device and
with a conventional mercury sphygmomanometer.
Statistical analyses
Anthropometric and blood pressure data are expressed as
mean
±
standard deviation. The
t
-test was used to compare the
significant differences between genders by age group. Linear
regression was performed to determine the relationship between
blood pressure, sum of four skinfolds and ratios of skinfolds,
both unadjusted and adjusted for age and gender. Logistic
regression was used to estimate the association between over-
fatness and the odd incident of hypertension, unadjusted and
adjusted for age and gender. All data were analysed with a
statistical package for social science (SPSS) version 25. The
statistical difference was set at
p
<
0. 05.
Results
Table 1 shows descriptive statistics for weight, height, body
mass index (BMI), systolic and diastolic blood pressure, triceps,
subscapular, biceps and supra-iliac skinfolds, sum of four
skinfolds, ST, SS and SSTB of Polokwane children aged five to
15 years. All variables showed significant differences between
girls and boys in other age groups except for SS/SSTB (trunk
ratio) and systolic blood pressure in all age groups. Girls showed
a higher sum of four skinfold mean values [29.6 (8.50) –44.1
(19.68)] in all age groups than boys [25.3 (8.36) –34.0 (19.83)],
and the difference was significant (
p
<
0.05). Girls also showed
higher BMI mean values [16.4 (3.1) –17.8 (3.6)] in age groups
eight to 10 and 11–15 years old than boys [15.9 (2.3) –16.9 (3.1)].
Yet again girls exhibited higher diastolic blood pressure [64.0
(9.3)] than boys [63.0 (10.2)] at age group five to seven years
old. Boys showed a non-significantly higher mean systolic blood
pressure value [92.1 (11.3)] than girls [91.4 (10.0)] in age group
five to seven years old.
Table 2 indicates the prevalence of over-fatness and
hypertension among Polokwane children aged five to 15 years.
The prevalence of over-fatness ranged from 7.3–12.3%, with girls
being more over-fat (10.1–12.3%) than boys (7.3–10.3%). There
was a high prevalence of hypertension in girls, ranging from
1.4–33.0%, who were more hypertensive than boys (3.6–21.3%).
Table 3 shows linear regression coefficients for the association
between systolic and diastolic blood pressure with the sum of
four skinfolds, and ratios ST, S/ST and SS/SSTB of Polokwane
children aged five to 15 years. Both systolic and diastolic blood
pressure showed a significant positive (
p
<
0.001) association
with the sum of four skinfolds and all skinfold ratios, unadjusted
and adjusted for age and gender, except for the association
between S/ST and diastolic blood pressure, which showed a
significant association only when unadjusted (beta ranged
between 0.29 and 62.08, 95% CI ranged between 0.26 and 0.33
and 49.00 and 75.17).
Table 4 shows the odds ratio and 95% CI for the association
of over-fatness and high blood pressure among Polokwane
children aged five to 15 years. There was a significant positive (
p
Table 1.The descriptive statistics of weight, height, BMI, systolic and
diastolic blood pressure, triceps, subscapular, biceps and supra-iliac
skinfolds, the sum of four skinfolds, ST, S/ST and SS/SSTB of Polokwane
private school children aged five to 15 years (
n
=
1 665)
Variable
5–7 years
8–10 years
11–15 years
Boys
mean
(SD)
Girls
mean
(SD)
Boys
mean
(SD)
Girls
mean
(SD)
Boys
mean
(SD)
Girls
mean
(SD)
Number
192
216
339
327
315
276
Triceps (cm)
8.8
(2.85)*
9.8
(2.85)*
9.9
(4.62)**
11.5
(4.37)**
11.1
(5.59)**
13.0
(5.14)**
Subscapular
(cm)
5.8
(1.82)**
6.6
(1.90)**
6.8
(3.52)**
8.51
(4.39)**
7.8
(4.58)**
10.3
(5.35)**
Biceps (cm)
4.4
(1.39)**
5.3
(1.85)**
4.9
(2.28)**
6.8
(3.41)**
5.2
(2.79)**
8.2
(3.97)**
Supra-iliac
(cm)
6.2
(3.09)**
7.9
(3.12)**
8.1
(5.73)**
10.0
(5.50)**
9.9
(7.79)**
12.6
(6.63)**
Sum of four
skinfolds (cm)
25.3
(8.36)**
29.6
(8.50)**
29.7
(15.47)**
36.8
(16.47)**
34.0
(19.83)**
44.1
(19.68)**
ST
0.7
(0.13)
0.7
(0.15)
0.7
(0.14)*
0.7
(0.16)*
0.7
(0.15)**
0.8
(0.17)**
S/ST
0.4
(0.05)
0.4
(0.05)
0.4
(0.05)*
0.4
(0.05)*
0.4
(0.05)**
0.4
(0.05)**
SS/SSTB
0.5
(0.04)
0.5
(0.05)
0.5
(0.05)
0.5
(0.05)
0.5
(0.05)
0.5
(0.05)
Weight (kg)
23.3
(3.9)
22.4
(3.7)
29.8
(6.1)*
31.3
(7.9)*
38.6
(9.1)**
42.3
(10.8)**
Height (m)
125.3
(6.1)
124.2
(7.1)
136.5
(8.0)
137.5
(8.0)
150.3
(8.2)**
153.5
(8.3) **
BMI (kg/m
2
)
14.8
(1.6)
14.5
(1.7)
15.9
(2.3)*
16.4
(3.1)*
16.9
(3.1)*
17.8
(3.6) *
Systolic BP
(mmHg)
92.1
(11.3)
91.4
(10.0)
100.4
(11.1)
101.4
(12.7)
107.2
(13.1)
110.3
(13.8)
Diastolic BP
(mmHg)
63.0
(10.2)**
64.0
(9.3)**
68.5
(9.4)
68.3
(9.2)
70.6
(11.0)
72.8
(11..5)
*
p
<
0.05; **
p
<
0.001; SD
=
standard deviation; S/T
=
ratio of subscapular-to-
triceps skinfolds, S/ST
=
ratio of subscapular-to-subscapular
+
triceps skinfolds;
SSTB
=
ratio of trunk-to-limb skinfolds (subscapular
+
supra-iliac
+
biceps
+
triceps); SS
=
trunk ratio (subscapular
+
supra-iliac).
Table 2.The prevalence of over-fatness, high systolic and
diastolic blood pressure and hypertension among Polokwane
private school children aged five to 15 years
Variable
5
–
7 years
8
–
10 years
11
–
15 years
Boys
n
=
192
% (
n
)
Girls
n
=
216
% (
n
)
Boys
n
=
339
% (
n
)
Girls
n
=
327
% (
n
)
Boys
n
=
315
% (
n
)
Girls
n
=
276
% (
n
)
Over-fatness
7.3
(14)
10.2
(22)
10.3
(35)
10.1
(33)
9.8
(31)
12.3
(34)
High systolic BP 4.2
(8)
2.3
(5)
11.2
(38)
18.0
(59)
30.8
(97)
40.9
(113)
High diastolic BP 21.9
(42)
24.1
(52)
36.6
(124)
36.4
(119)
47.3
(149)
57.2
(158)
Hypertension
3.6
(7)
1.4
(3)
7.4
(25)
14.1
(46)
21.3
(67)
33.0
(91)