CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 5, June 2012
262
AFRICA
few cases of overweight and obese children seen in this study
were from families of a high socio-economic class, in contrast
with what is seen in developed countries.
In our earlier study on the same population,
25
there was a
high prevalence of under-nutrition, which was associated with
a high prevalence of moderate to vigorous physical activity
among these adolescents. This suggests that there is a negative
balance between energy intake and the energy expended in
doing exercise. However, even though the mean BMI in this
study was as low as 17.1 kg/m
2
, as much as 25.8% of the
children had centrally accumulated fat. This is similar to the
findings in the Karimojong children of Uganda
26
and middle-
aged Indians,
27
and is a characteristic feature of populations with
chronic malnutrition. This phenomenon, coupled with adaptation
to western lifestyles, could explain the rise in prevalence of
non-communicable diseases such as hypertension and diabetes
mellitus in these populations.
The prevalence of elevated blood pressure in this study is
similar to the 3.7% obtained earlier by Bugaje
et al.
28
in Zaria,
Nigeria and the 4% obtained by Balogun
et al.
29
in Ile-Ife,
Nigeria. It is lower than the prevalence of 6.69% in India,
30
9.5% in Ilorin,
31
Nigeria, and 12–23% among adolescents in
Quebec, Canada.
32
The upsurge in the prevalence of overweight
and obesity, which varies between populations depending on
their lifestyle, socio-economic status and other environmental
interactions, has been implicated in the differences in prevalence
of high blood pressure at a national and international level.
In this study, general obesity was a good predictor of high
SBP in males, and WC was a good predictor of high SBP and
DBP in males. Surprisingly, despite a higher prevalence of
children who had a BMI above the 90th percentile had a WC
above the 75th percentile (
χ
2
=
55.8,
p
<
0.001).
Both SDP and DBP increased significantly with age (
r
=
0.341,
p
=
0.000;
r
=
0.193,
p
=
0.000, respectively). The mean
DBP was significantly higher in females (62.7 vs 59.0 mmHg,
p
<
0.001). Eleven children (2.6%) had high SBP and another
14 (3.3%) had high DBP. There was no significant gender
difference in the prevalence of high SBP and high DBP (
p
=
0.206,
p
=
0.697, respectively).
The weight, height, BMI and WC had a positive and
statistically significant correlation coefficient with SBP and DBP
(
r
=
0.126–0.421,
p
<
0.05). The correlation coefficient of BMI
with SBP was higher than that of WC with SBP (0.327 vs 0.29).
Similarly, the correlation coefficient of BMI with DBP was
higher than that of WC with DBP (0.189 vs 0.129).
Table 2 show the relationship between general obesity and
blood pressure. There was a significantly higher prevalence of
high SBP among male children with general obesity (
χ
2
=
36.5,
p
<
0.001). Among the children with central obesity, a significantly
higher prevalence of high SBP (
χ
2
=
22.3,
p
< 0.001) and high
DBP (
χ
2
=
4.1,
p
<
0.042) was seen in only the males (Table 3).
In a simple linear regression analysis, BMI and WC explained
10.7 and 8.4%, respectively of the variance in SBP, and 3.6
and 2.7%, respectively of the variance in DBP. Each increment
in BMI increased SBP and DBP by 0.327 and 0.189 mmHg,
respectively, while each increment in WC increased SBP
and DBP by 0.29 and 0.164 mmHg, respectively. When the
effects of BMI and WC on blood pressure were studied in a
multiple logistic regression equation model (Table 4), BMI
was significantly associated with high SBP (OR 0.8, 95% CI:
0.65–0.99,
p
<
0.05).
Discussion
Similar to previous studies from Nigeria,
21-23
the prevalence
of overweight and obesity from this study (using BMI as the
indicator) was low when compared with children in the UK,
3
Canada
4
and the USA.
5
It was also lower than the prevalence
recorded in many North African, Middle Eastern and Latin
American countries
24
and in South Africa,
6
where the prevalence
of overweight and obesity has been rapidly increasing. This
finding supports the fact that overweight and obesity is still an
emerging nutritional problem affecting children in Nigeria. The
TABLE 4. MULTIPLE REGRESSIONS OF BODY MASS
INDEXANDWAIST CIRCUMFERENCEAS RISK
FACTORS FOR HIGH BLOOD PRESSURE*
Beta coefficient Standard error
p
-value
Systolic blood pressure
BMI
–0.223
0.109
0.042
WC
0.029
0.047
0.530
Diastolic blood pressure
BMI
–0.177
0.118
0.136
WC
0.013
0.053
0.316
*Adjusted for age and gender.
TABLE 3. RELATIONSHIP BETWEENWAIST
CIRCUMFERENCEAND BLOOD PRESSURE
Systolic blood pressure,
n (%)
Diastolic blood pressure,
n (%)
WC percentile
Normal
High
Normal
High
Males
≤
75th
197 (100)
0 (0.0)
193 (98)
4 (2.0)
>
75th
32 (88.9)
4 (11.1)* 33 (91.7)
3 (8.3)*
Females
≤
75th
113 (96.6)
4 (3.4)
113 (96.6)
4 (3.4)
>
75th
70 (95.9)
3 (4.1)
70 (95.9)
3 (4.1)
Total
≤
75th
310 (98.7)
4 (1.3)
306 (97.5)
8 (2.5)
>
75th
102 (93.6)
7 (6.4)* 103 (94.5)
6 (5.5)
*
p
<
0.05
TABLE 2. RELATIONSHIP BETWEEN BODY
MASS INDEXAND BLOOD PRESSURE
Systolic blood pressure,
n (%)
Diastolic blood pressure,
n (%)
BMI percentile
Normal
High
Normal
High
Males
≤
90th
225 (99.1)
2 (0.9)
220 (96.9)
7 (3.1)
>
90th
4 (66.7)
2 (33.3)* 6 (100)
0 (0.0)
Females
≤
90th
168 (96)
7 (4.0)
169 (96.6)
6 (3.4)
>
90th
15 (100)
0 (0.0)
183 (96.3)
7 (3.7)
Total
≤
90th
393 (97.8)
9 (2.2)
389 (96.8)
13 (3.2)
>
90th
19 (90.5)
2 (9.5)* 20 (95.2)
1 (4.8)
*
p
<
0.05
