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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 5, September/October 2019
AFRICA
259
appropriate arm-size cuffs and blood pressure was measured at
three-minute intervals using the Omron (Hem 7120) automated
blood pressure machine. The mean of three recordings of systolic
(SBP) and diastolic blood pressure (DBP) and heart rate (HR)
were computed. SBP and DBP were converted to percentiles for
age, gender and height for each child, based on the Paediatric
Task Force standards.
14
Both waist (WC) and hip circumference (HC) were measured
using the World Health Organisation guidelines.
15
Participating
children were requested to stand upright with feet together
and arms hanging freely at the sides. WC was measured at the
smallest circumference of the waistline with a non-stretch tape.
Boys and girls were requested to dress lightly on days of data
collection. HC was measured at the largest circumference around
the greater trochanter of the femur.
15
Height was measured using a stadiometer. Boys and girls were
requested to take off their shoes and to step on the stadiometer
platform with feet together and close to the stadiometer rod. The
movable bar was lowered to just touch the head. Height was read
off to the nearest cm.
Personal data such as height, age and gender were entered
into the Omron body composition monitor (BF511). Then each
child was requested to step onto the electrode pads of the body
composition monitor and hold the arm piece tightly in both
hands, with arms held out at right angles to the body, until the
equipment stopped scanning. The equipment displayed weight,
body mass index (BMI) and total fat mass (TFM). BMI was
converted to percentiles for age and gender.
Statistical analysis
Data were analysed using Stata version 14. Data were checked
for normality, and differences between the means of normally
distributed data were assessed using the
t
-test or ANOVA with
Dunnet’s test, while the Kruskal–Wallis test with Friedman’s
post hoc
test was used for skewed data. Spearman’s correlation
coefficient (
r
) was used to determine the relationships between
blood pressure parameters and selected measures of adiposity.
Adiposity was categorised as lean with BMI
<
85th percentile
or ≤ 75th percentile for WC, HC or TFM for gender, and
overweight/obesity as BMI ≥ 85th percentile or
>
75th percentile
of WC, HC and TFM for gender. Fisher’s exact test was used
to determine the relative risk for hypertension associated with
overweight/obesity as determined for the four selected measures
of adiposity. Statistical significance was set at
p
≤ 0.05.
Results
A total of 540 10- to 14-year-old boys and girls were recruited
into this study. Male and female participants were of similar ages.
Females had significantly (
p
<
0.05) higher BMI, WC, HC, TFM,
waist-to-height ratio (WHtR), SBP and DBP (Table 1). On the
other hand pulse pressure (PP) was similar for males and females.
The prevalence of overweight was 10.9% in the total cohort
and was higher in the girls (13.5%) compared to boys (8.0%). The
prevalence of obesity was 14.0% in the total cohort, 12.8% in the
boys and 15.2% in the girls (Table 2). Similarly, the prevalence of
pre-hypertension and hypertension were higher in girls compared
to boys.
In order to better understand the relationship between
blood pressure and measures of adiposity (BMI, WC, TFM,
WHtR), Spearman’s rank correlations were performed. Pairwise
correlations between SBP, DBP, PP, BMI, WC, TFM and WHtR
were positive in both boys and girls. BMI, WC, TFM and WHtR
correlated modestly with SBP and PP in females (Table 3). Only
BMI had a weak correlation with SBP and PP in males. On
the other hand there was no correlation between DBP and all
measures of adiposity in boys or girls.
In order to determine the effect of selectedmeasures of adiposity
on blood pressure values, boys and girls were classified according to
their adiposity (BMI, WC, TFM, WHtR) quartiles. SBP, DB and
PP [PP = (SBP – DBP)] for each quartile were computed and the
prevalence of hypertension and pre-hypertension in each quartile
was determined. SBP, DBP and PP increased progressively from
the first quartile (lowest adiposity) to the fourth quartile (highest
adiposity). The prevalence of hypertension and pre-hypertension
were highest in the fourth quartile for all measures of adiposity.
The first quartiles for all measures of adiposity had the lowest
levels of SBP, DBP, HR and PP. It also had the lowest prevalence
of hypertension and pre-hypertension (Table 4).
Table 1. Characteristics of the learners by gender
Characteristics
Boys
Girls
Number
250
290
Age (years)
11.9 ± 0.6
11.9 ± 0.5
BMI (kg/m
2
)
18.9 ± 0.2
20.2 ± 0.3*
WC (cm)
65.4 ± 0.7
69.2 ± 0.7**
TFM (%)
22.5 ± 0.01
24.1 ± 0.01**
HC (cm)
80.1 ± 0.6
85.6 ± 0.7**
WHtR
0.44 ± 0.01
0.46 ± 0.00**
SBP (mm Hg)
110.1 ± 0.7
112.7 ± 0.6*
DBP (mm Hg)
70.6 ± 0.5
73.1 ± 0.4*
PP (mm Hg)
39.5 ± 0.5
39.5 ± 0.0.4
Calculated percentages were cohort specific.
BMI: body mass index, WC: waist circumference, TFM: total fat mass, HC: hip
circumference; WHtR: waist-to-height ratio, SBP: systolic blood pressure, DBP:
diastolic blood pressure, PP: pulse pressure.
*
p
<
0.05, **
p
<
0.01.
Table 2. Prevalence of overweight, obesity, pre-hypertension
and hypertension
Variables
Overweight
Obesity Pre-hypertension Hypertension
Total cohort,
n
(%)
59 (10.9)
76 (14.0)
66 (12.2)
112 (20.7)
Boys,
n
(%)
20 (8.0)
32 (12.8)
28 (11.2)
39 (15.6)
Girls,
n
(%)
39 (13.5)
44 (15.2)
45 (15.5)
76 (26.2)
Table 3. Spearman’s rank correlation coefficients between blood
pressure parameters and selected measures of adiposity
Spearman’s rank correlation coefficients
Variables
BMI (kg/m
2
) WC (cm) TFM (%)
WHtR
SBP (mmHg)
Boys
0.24*
0.12
0.10
0.11
Girls
0.39*
0.37*
0.33*
0.27*
DBP (mmHg)
Boys
0.07
0.09
0.07
0.09
Girls
0.08
0.07
0.08
0.06
PP (mmHg)
Boys
0.22
0.05
0.05
0.05
Girls
0.41*
0.38*
0.35*
0.32*
BMI: body mass index, WC: waist circumference, TFM: total fat mass, WHtR:
waist-to-height ratio, SBP: systolic blood pressure; DBP: diastolic blood pres-
sure, PP: pulse pressure. *
p
<
0.05.