CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 6, November/December 2010
320
AFRICA
may have played a role in the relatively low number of boys with
a body fat percentage above 20% in the study sample.
The CRP values of some of the children were above normal
concentrations. On interpretation of CRP values, low risk is
defined as a level less than 1 mg/l, average risk is 1.0–3.0 mg/l
and high risk is values of 3–10 mg/l.
18
In this study, when subjects
with markedly increased CRP levels (
>
10 mg/l) were excluded,
a significant association was observed between physical activity
and CRP levels in the girls and between fitness and CRP levels in
the boys. The relevance of such findings in adolescents is useful
because CRP level is proven to predict the development of type
2 diabetes and mortality.
5,30
Future risk can therefore be assessed
in adolescents.
Smoking is a well-known predictor of high serum CRP
levels.
19
Only 5.7% of the children admitted to smoking and
among those who smoked, only one was a girl. Adjustment for
smoking in the correlation analyses did not, however, make any
difference to previously non-significant correlations. In this
low-income setting, children could probably not afford to smoke
regularly.
A larger number of girls in comparison with boys were clas-
sified as over-fat. Only 15 out of a total of 85 boys had a fat
percentage higher than the cut-off of 20%. Out of 134 girls,
only 35 had a fat percentage equal to or below 25%, with 101
girls having fat percentages above this norm.
31
According to
Monyeki
et al
.,
8
obesity is not only common in South African
women, but also in female adolescents. Adolescence is one of
the most vulnerable periods for the development of overweight
and obesity.
2,3
The girls in our study live in a low socio-economic environ-
ment, and it is possible that low physical activity and conse-
quently a low fitness level played a role in the development of
their high body fat percentages. Almost 50% of the girls were
in Tanner stages 4 and 5 and 74% of the girls had a body fat
percentage above 25%, compared to 71% of the boys in Tanner
stages 4 and 5, but only 18% of them had a body fat percentage
above 20%.
With regard to skin folds, the greatest difference between the
group of boys with a body fat percentage above 20% and the
group with a normal body fat percentage was for the abdominal
skin fold. This indicates that fat accumulation in this group of
boys was mainly in the abdominal area.
Tables 3 and 4 show the differences in body composition and
fat distribution between the boys and girls. The girls had greater
skin fold thicknesses than the boys, but smaller WHR, indicat-
ing more abdominal fat distribution in the boys, compared to
more peripheral fat distribution in the girls. This difference in
body composition between the boys and girls is probably the
main reason for the gender differences found in the associations
between body composition and serum CRP levels. It is well-
known that adolescent girls generally have a larger proportion of
body mass as fat, and are more likely to deposit fat subcutane-
ously and on their hips, whereas adolescent boys are more likely
to have more muscle mass and they deposit fat in the abdominal
region, as shown in Tables 4 and 5. Oestrogen levels appear to
underlie many of these gender differences.
32
The release of IL-6 from the visceral adipose tissue may
induce low-grade systemic inflammation in subjects with
increased body fat. This may explain the association between
BMI and CRP levels.
16,19
Although in this study there was no
statistically significant difference between the serum CRP levels
of children with a normal body fat percentage versus those with
a high body fat percentage, serum CRP values correlated posi-
TABLE 4. DESCRIPTIVE STATISTICS FOR BOYSWITH
HIGH BODY FAT PERCENTAGEVERSUS BOYSWITH
NORMAL BODY FAT PERCENTAGE
Body fat %
>
20%
(
n
=
70)
Body fat %
>
20%
(
n
=
15)
Variable
Mean/
number
Standard
deviation/%
Mean/
number
Standard
deviation/%
Age (years)
15.88
1.56
15.65
1.44
Weight (kg)
#
47.96
8.55
53.80 14.46
Height (cm)
161.31
8.66 159.51 10.30
BMI (kg/m
2
)
#
18.32
2.28
20.87
3.69
Waist circumference (cm)
65.11
4.94
69.60
7.12
WHR
0.84
0.06
0.83
0.04
Triceps skin fold (mm)
#
7.74
2.60
14.14
6.28
Sub-scapular skin fold (mm)
#
7.18
1.82
12.20
8.18
Abdominal skin fold (mm)
#
9.50
4.33
21.32 11.01
Fat %
#
16.16
4.21
29.62
4.23
Muscle mass (kg)
40.45
7.49
37.99 10.50
Tanner stage 1* (–)
0
0
0
0
Tanner stage 2*
(14.9
±
0.7, 13–15 years)
6
8.6% 1
6.7%
Tanner stage 3*
(15.0
±
1.2, 13–17 years)
14
20% 4
26.6%
Tanner stage 4*
(16.0
±
1.3, 14–18 years)
44
62.8% 9
60%
Tanner stage 5*
(16.8
±
1.0, 15–18 years)
6
8.6% 1
6.7%
Median
Interquartile
range
Median
Interquartile
range
CRP (mg/l)
0.39 0.15–0.90 0.59 0.20–1.65
Differentiated on account of fat percentage, boys with fat percentages
>
20%
were classified over- fat, according to Lohman.
28
*Tanner stage based on genital development stage (1
=
no development, 5
=
mature)
21
with age, mean
±
SD (range),
#
significant differences between groups.
BMI: body mass index; CRP: serum C-reactive protein concentration; WC:
waist circumference; TSF: triceps skin fold.
TABLE 5. DIFFERENCES BETWEENANTHROPOMETRIC
VARIABLESAND CORRELATION BETWEEN PERCENTAGE
BODY FATANDANTHROPOMETRICVARIABLES IN BOYSAND
GIRLSWITHA HIGH BODY FAT PERCENTAGEVERSUS BOYSAND
GIRLSWITHA NORMAL BODY FAT PERCENTAGE
Correlation coefficient (level of significance) for the correlation between
percentage body fat and skin-fold thickness
Boys
Girls
Variable
Body fat
%
>
20%
(
n
=
70)
Body fat %
>
20%
(
n
=
15)
Body fat
%
>
20%
(
n
=
35)
Body fat %
>
20%
(
n
=
101)
Triceps skin fold (mm)
0.16
(NS)
0.63
(
p
=
0.001)
0.33
(NS)
0.63
(
p
=
0.001)
Sub-scapular (mm)
–0.03
(NS)
0.67
(
p
<
0.0001)
0.25
(NS)
0.67
(
p
<
0.0001)
Abdominal (mm)
0.28
(
p
=
0.04)
0.68
(
p
<
0.0001)
0.37
(
p
=
0.05)
0.68
(
p
<
0.0001)
Percentage difference between groups of boys and girls
Boys with body fat %
>
20% compared with
boys with body fat %
>
20%
Girls with body fat %
>
25% compared with
girls with body fat %
>
25%
Body weight (kg)
12.13%
17.78%
Waist circumference (mm)
6.9%
9.5%
Percentage body fat
83.3%
55.6%
