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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 5, September/October 2019
260
AFRICA
Boys and girls were separated into lean and overweight/
obese groups using selected measures of adiposity. BMI
<
85th
percentile was classified as lean and BMI ≥ 85th percentile as
overweight/obese. WC, TFM and WHtR were separated into two
groups: ≤ 75th percentile for gender was classified as lean while
>
75th percentile was classified as overweight/obese. A greater WC
conferred a 1.7-times greater risk of developing hypertension (
p
= 0.008) in the cohort. The relative risk of having hypertension
conferred by high BMI, WC, WHtR and TFM was absent in
boys but weak and not significant in girls (Table 5).
Discussion
In this study we showed that the prevalence of overweight
and obesity in 10- to 14-year-old children in the Eastern
Cape was over 10 and 14%, respectively, while the prevalence
of pre-hypertension and hypertension were 12 and 20%,
respectively. Gender-specific analysis showed that the girls were
more obese and also had a higher prevalence of hypertension
and pre-hypertension. Although the relative risk of having
hypertension with increasing adiposity was small, children whose
BMI, WC, TFM and WHtR were higher than the third quartile
had significantly (
p
<
0.05) higher blood pressure than those in
the lower quartiles.
Using all four selected measures of adiposity (BMI, WC,
TFM and WHtR) our study showed that girls were larger and
had a higher prevalence of overweight and obesity. Participants
in this study were 10 to 14 years old, which is a period of much
hormonal activity. Puberty begins in girls from eight to 12 years
old, while in boys it begins from nine to 14 years old. This period
in girls corresponds with an increase in BMI, and changes in body
fat composition and distribution, while in boys it is a period of fat
loss and muscle development,
16
thus explaining the differences in
BMI, WC, TFM and WHtR between boys and girls.
Several studies have shown an association between BMI and
blood pressure.
17,18
A Brazilian study showed that overweight and
obese children had a 3.6-fold greater risk of having higher SBP
and 2.7-times increased risk for higher DBP.
19
Both SBP and
DBP as well as PP were higher in the girls than boys. The growth
spurt of puberty, which is often accompanied by a rise in blood
pressure,
20
occurs earlier in girls than in boys, thus explaining the
higher blood pressure in girls.
The current study showed a difference in the prevalence of
hypertension and pre-hypertension when overweight/obesity
was classified as the fourth quartile of WC, TFM and WHtR.
An increased WC is a known risk for metabolic diseases in
both children
21
and adults. We have previously shown that BMI,
TFM, WC and WHtR correlated similarly with SBP and PP in
females, although these relationships were different in males.
These results further strengthen the suggestion that the 10- to
14-year-old girls involved in the study were mostly pubertal
and therefore increased adiposity contributed to higher blood
pressure in the girls. Furthermore, another study showed that
children who had low BMI but high WC were at great risk of
developing hypertension.
22,18
Our results show that children with WC and HC greater than
the 75th percentile had an increased relative risk (1.7 and 1.5,
respectively) of being hypertensive. This finding was confirmed
by the fact that both pre-hypertension and hypertension were
over 1.5 times more prevalent in 10- to 14-year-old girls
compared to age-matched boys. On the other hand, higher BMI
did not confer a significant risk of higher BP. However when
subjects were separated into quartiles for BMI, WC, TFM and
WHtR, it was noted that SPB, DBP and PP were significantly
higher in boys and girls in the fourth quartile, indicating that
adiposity contributes to blood pressure levels.
Table 5. Relative risk of having hypertension with
high measures of adiposity
Relative risk
Variables
Cohort
Males
Females
BMI
1.04
1.05
1.28
95% CI
0.544–1.975
0.652–1.716
0.974–1.675
p
-value
0.86
0.862
0.090
WC
1.71
1.203
1.328
95% CI
1.284–2.279
0.774–1.870
1.003–1.758
p
-value
0.0008
0.418
0.06
TFM
1.42
0.859
1.384
95% CI
0.891–2.00
0.539–1.370
0.877–1.558
p
-value
0.183
0.542
0.189
WHtR
1.27
1.245
1.26
95% CI
0.766–2.119
0.790–1.961
0.956–1.671
p
-value
0.351
0.385
0.133
BMI: body mass index, WC: waist circumference, TFM: total fat mass, WHtR:
waist-to-height ratio, CI: confidence interval.
Table 4. Components of blood pressure in the four quartiles of BMI,WC,
TFM andWHtR
Parameters
1st
quartile
2nd
quartile
3rd
quartile
4th
quartile
p-value
BMI
SBP (mmHg) 107.1 ± 1.5 110.4 ± 0.5 113.9 ± 1.0** 117.3 ± 1.1**
##
0.0001
DBP (mmHg) 69.1 ± 1.1 71.8 ± 0.4 73.4 ± 0.8* 73.3 ± 0.9*
0.03
HR (beats/min) 87.9 ± 1.9 87.3 ± 0.7 84.9 ± 1.6
89.3 ± 1.3
0.14
PP (mmHg)
38.1 ± 1.3 38.7 ± 0.4 40.4 ± 0.9
##
44.1 ± 0.9
##
0.0001
HT,
n
(%)
3 (8.8)
59 (16.1)
14 (23.7)
13 (16.5)
preHT,
n
(%)
9 (26.5) 125 (34.2)
23 (39.0)
34 (44.7)
TFM
SBP (mmHg) 108.8 ± 0.9 110.2 ± 0.9 112.2 ± 0.9** 114.9 ± 0.8**
##
0.0001
DBP (mmHg) 70.6 ± 0.7 71.7 ± 0.7 72.4 ± 0.9
73.0 ± 0.6
0.14
HR (beats/min) 87.5 ± 1.1 86.1 ± 1.1 88.5 ± 1.2
87.7 ± 1.0
0.50
PP (mmHg)
38.2 ± 0.7 38.5 ± 0.7 39.8 ± 0.7 42.0 ± 0.7**
##
0.0001
HT,
n
(%)
17 (12.8) 20 (14.8)
23 (11.8)
28 (20.1)
preHT,
n
(%)
37 (27.8) 46 (34.1)
48 (24.6)
58 (43.6)
WC
SBP (mmHg) 108.1 ± 0.8 109.8 ± 0.9 112.3 ± 1.1** 115.8 ± 0.7**
##
0.0001
DBP (mmHg) 70.9 ± 0.6 71.2 ± 0.7 71.7 ± 0.7* 73.7 ± 0.6*
0.05
HR (beats/min) 86.8 ± 1.1 87.6 ± 1.1 87.1 ± 1.2
89.3 ± 1.3
0.78
PP (mmHg)
37.2 ± 0.6 38.6 ± 0.7 40.7 ± 0.9
##
42.1 ± 0.6
##
0.001
HT,
n
(%)
25 (16.7) 27 (18.9)
19 (20.4)
46 (29.7)
preHT,
n
(%)
49 (32.9) 44 (30.8)
31 (33.3)
69 (44.5)
WHtR
SBP (mmHg) 109.0 ± 0.9 111.1 ± 0.9 110.6 ± 0.9 115.4 ± 0.8***
##$$$
0.0001
DBP (mmHg) 71.0 ± 0.7 72.3 ± 0.7 71.0 ± 0.6
73.3 ± 0.6*
$
0.05
HR (beats/min) 86.9 ± 1.1 87.1 ± 1.2 88.1 ± 1.1
87.3 ± 1.0
0.75
PP (mmHg)
37.9 ± 0.6 38.8 ± 0.7 39.6 ± 0.7 42.1±0.7***
###$
0.0001
HT,
n
(%)
19 (14.1) 26 (19.3)
28 (20.6)
40 (30.1)
preHT,
n
(%)
37 (27.4)
54 (40)
42 (30.9)
59 (44.4)
BMI: body mass index, WC: waist circumference, TFM: total fat mass, WHtR:
waist-to-height ratio, HT: hypertension; preHT: pre-hypertension, SBP: systolic
blood pressure; DBP: diastolic blood pressure, HR: heart rate, PP: pulse pressure.
*Compared to first quartile (*
p
<
0.05, **
p
<
0.01, ***
p
<
0.001),
#
compared to
second quartile (
#
p
<
0.05,
##
p
<
0.01,
###
p
<
0.001) and
$
comparing quartile 4 to
quartile 3 (
$
p
<
0.05,
$$
p
<
0.01;
$$$
p
<
0.001).