CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 5, June 2012
AFRICA
261
from the Ogun State Ministry of Education.
The teachers, pupils and parents were well informed on the
scope and extent of the survey. Consent was obtained from
the parents and pupils. At the time of the survey, there was a
total of 322 schools in Abeokuta (the ratio of public to private
primary schools was 1:1, while the ratio of public to private
secondary schools was 3:1). Using the multistage random-
sampling technique, seven schools comprising two private and
one public primary school, and one private and three public
secondary schools were selected by balloting. The basis for
this selection was because the number of students in the public
primary schools was higher than that in private primary schools,
whereas in the secondary schools the numbers were about equal.
From each of the selected schools, all grades were studied
(primary, grades 1–6; junior and senior secondary, grades 7–12).
On the day of the study, one section of each grade was
selected by balloting. Ballot papers were served to all the
children in the selected section. These ballot papers were blank
except those that were marked with numbers 1 to 15. After all the
students had picked a paper, they were asked to open them and
those with numbers 1 to 15 were selected. Ninety pupils were
selected from each of the seven schools. In all, 630 pupils were
selected but only 570 (90.5%) pupils completed the study. The
other 60 pupils were excluded based on refusal to participate and
evidence of chronic diseases.
Blood pressure was not measured in 147 children aged five
to nine years due to non-availability of an appropriate cuff.
Each student was interviewed to obtain information on the
demographic and socio-economic characteristics of the child’s
family. The families were assigned a socio-economic class using
the modified method recommended by Oyedeji.
16
Trained student nurses took all anthropometric measurements.
Each measurement was taken by the same examiner to minimise
measurement error. The children were weighed using an
electronic scale calibrated in 100-g units (SECA/UNICEF,
Australia). All children were weighed wearing only underwear
and to the nearest 0.1 kg.
The height was measured using a specifically made wooden
stadiometer with a steel tape measure. This was done with the
child standing erect without shoes and with the eyes looking
horizontally and the feet together on a horizontal base. These
measurements were done to the nearest 0.1 cm. BMI was
calculated by dividing the weight (kg) by the square of the height
(m).
Waist circumference was measured midway between the iliac
crest and the lowermost margin of the ribs with bare belly and at
the end of normal expiration, according to the WHO guidelines.
17
Standardisation checks on the weighing scale, height boards and
tape measure were done periodically during the study period.
For blood pressure measurements, the subjects were seated
and rested for five minutes. An appropriately sized cuff, covering
at least two-thirds of the upper right arm with the lower border
not less than 2.5 cm from the cubital fossa, was applied after
restrictive clothing had been removed. Thereafter blood pressure
was measured twice using an automatic blood pressure monitor
(HEM-712C; Omron, China) and the mean was recorded.
BMI is widely used as an index of general obesity although
the cut-off points vary between the 85th and 97th percentiles.
18
In this study, obesity was defined as BMI at or above the 95th
percentile of age- and gender-specific data. A child was regarded
as having central obesity if the WC was
≥
the 75th percentile
for age- and gender-specific data, as proposed by Fernandez
et
al
.
19
Systolic (SBP) and diastolic blood pressures (DBP) were
defined as high when they were
≥
the 90th percentile, according
to the Task Force on High Blood Pressure in Children and
Adolescents.
20
Statistical analysis
Data analysis was by descriptive and inferential statistics,
using the SPSS for Windows software version 13. The means
and standard deviations (SD) of the weight, height, BMI,
WC, and SBP and DBP were calculated according to gender.
Gender differences in anthropometric and blood pressure
values were compared using the independent-samples
t-
test,
while proportions and ratios were compared using the Pearson
Chi-squared (
χ
2
) test. Simple and multiple logistic regression
analyses were carried out on BMI and WC using blood pressure
as the dependent variable. A probability (
p
) value of less than
0.05 was accepted as statistically significant.
Results
A total of 423 subjects with ages ranging from 10 to 19 years
had complete data sets, which were analysed. The mean age
was 13.2
±
2.41 years and 233 (55.1%) were males. The social
distribution shows that 166 (29.1%), 304 (53.3%) and 100
(17.5%) children belonged to the upper, middle and lower socio-
economic classes, respectively. Table 1 shows the means (
±
SD)
of the various anthropometric measures according to gender. All
the anthropometric measures increased with age in both genders.
The mean weight, BMI and WC were significantly higher in the
females (
p
<
0.05,
p
<
0.001,
p
<
0.001, respectively).
The BMI of the study population ranged from 11.59 to
34.14 kg/m
2
with a mean value of 17.1 kg/m
2
. Twenty-one
(5%) children were obese, 16 (76.2%) of them females, which
was statistically significant (
p
=
0.012). WC ranged from 50.5
to 97 cm and 109 (25.8%) children had a WC above the 75th
percentile for the population age and gender. There was a
significantly higher prevalence of central obesity among females
than males (38.4 vs 15.5%,
p
=
0.000). Twenty (95.2%) of the
TABLE 1. ANTHROPOMETRICAND BLOOD
PRESSUREVALUES OF THE STUDY
SUBJECTSACCORDINGTO GENDER
Variable
Total
(
n
=
423)
Male
(
n
=
233)
Female
(
n
=
190)
p
-value
Age (years)
13. 7 (2.4)
13.7 (2.4)
13.8 (2.4)
0.688
Weight (kg)
39.3 (11.2) 38.0 (11.5) 40.7 (10.7) 0.013
Height (cm)
149.7 (13.6) 150.2 (14.8) 149.1(12.1) 0.418
BMI (kg/m
2
)
17.1 (2.7)
16.4 (2.1)
18.0 (3.1)
0.000
WC (cm)
63.8 (8.5)
61.5 (5.9) 66.7 (10.1) 0.000
SBP (mmHg)
106.9 (11.5) 105.9 (10.9) 108.2 (12.2) 0.05
DBP (mmHg)
60.6 (10.4) 59.0 (10.1) 62.7 (10.4) 0.000
BMI
>
2 SD 21 (5.0)
6 (2.6)
15 (7.9)
0.012
WC
>
75th
percentile
109 (25.8)
36 (15.5)
73 (38.4)
0.000
High SBP
11 (2.6)
4 (1.7)
7 (3.7)
0.206
High DBP
14 (3.3)
7 (3.0)
7 (3.7)
0.697
