CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 6, November/December 2010
AFRICA
317
associated with increased blood pressure,
11
plasminogen activator
inhibitor-1 activity, plasma fibrinogen and the thrombin–anti-
thrombin complex,
12
as well as higher fasting plasma insulin and
leptin levels and insulin resistance. These possibly increase the
risk for cardiovascular disease.
13
No South African studies on
body composition and low-grade inflammation in children or
adolescents could be found in the literature.
C-reactive protein (CRP), synthesised in the hepatocytes, is
an acute-phase reactant that responds non-specifically
to infec-
tions, immuno-inflammatory diseases and malignancies.
14
CRP
is also a surrogate marker for interleukin (IL)-6 activity and is
proven to predict the development of type 2 diabetes and mortal-
ity.
15
Levels of CRP are usually low or undetected in healthy
subjects, but they increase up to 100 times during acute illness
or inflammation.
16
In the absence of infection, elevations of CRP
levels, generally below 10 mg/l, are associated with an increased
risk of the development of atherosclerotic cardiovascular disease.
In recent years CRP values, as measured by a high-sensitivity
assay (hs-CRP), have been recognised as a useful and sensitive
predictor of the future risk of myocardial infarction and stroke.
17
Pepys and Hirschfield
14
noted that CRP values cannot be used
diagnostically, but should be interpreted with full knowledge of
all other clinical and pathological results. Upon interpretation
of CRP values, low-risk inflammation is defined as a level less
than 1 mg/l, average risk is 1.0–3.0 mg/l, and high-risk values
are 3–10 mg/l.
18
There is a link between basal inflammation, MS and obesity.
The release of IL-6 from the visceral adipose tissue may induce
low-grade systemic inflammation in subjects with increased
body fat, resulting in clinically raised CRP levels in obese
adults.
14,18
However, the limited number of studies on children
causes uncertainty about the clinical significance of inflamma-
tion in overweight children.
4,5,16,17,19
Body fatness and central body fat distribution are related to
an adverse risk profile in the youth.
17
A higher degree of cardio-
respiratory fitness has been shown to relate to a healthier meta-
bolic profile in children. Isasi
et al.
19
showed in a study in the
USA that CRP levels did not differ between boys and girls and
fitness level was inversely correlated to CRP in the boys. There
are, however, few data about the association between obesity,
physical activity and serum CRP concentrations in black South
African children.
Early assessment of the inflammatory status of South African
children could be useful to decrease CVD risks, particularly in
individuals at intermediate risk, such as overweight or physi-
cally inactive children. The purpose of this study was to assess
the association between serum C-reactive protein and physical
activity, as well as body composition in 193 black high-school
children aged 13 to 18 years from a township in South Africa.
Methods
This study was performed as part of the PLAY study (PhysicaL
Activity in the Young) on the effects of physical activity in chil-
dren. For the purposes of this study, baseline data were used for
cross-sectional analysis.
The PLAY study was approved by the Ethics Committee of
the North West University (Potchefstroom campus). All grade
9 children (13–18 years old) from two secondary schools, situ-
ated in a low-income area in Potchefstroom in the North West
Province of South Africa, were provided with a permission
form to be signed by their parents before inclusion in the study.
Permission was also obtained from the school principals and
consent from the children. In total 193 boys and girls were avail-
able for inclusion.
The children were picked up at the schools and brought to
the University metabolic unit on the study days. They started
at the blood station, where fasting blood samples were taken.
Thereafter body composition (height, weight, waist circumfer-
ence, skin folds, and body volume and density) was measured.
The children then received food and proceeded to the question-
naire stations (demographic, Tanner and PDPAR).
Data regarding age, gender, home language, socio-economic
status, housing, accessibility to water and electricity, smoking
status and general health of the children, as well as educational
level and occupation of the parents/caregivers were obtained
by individual interviews, performed by fieldworkers in each
subject’s language of preference.
Body composition and anthropometry
The subjects were measured and weighed in their under-
wear by trained postgraduate biokinetics students according to
standard ISAK (International Society for the Advancement of
Kinanthropometry) methods.
20
The height (cm) of the subjects
was taken with a vertical stadiometer to the nearest 0.1 cm. Body
weight was measured to the nearest 0.1 kg on an electronic scale
(Precision Health scale, A & D Co, Saitama, Japan). The scale
was calibrated with a 10-kg standardised weight.
Anthropometrical nutritional status was defined by Centers
for Disease Control (CDC)
z
-scores
21
and international body
mass index (BMI)-for-age cut-off points.
22
A flexible steel meas-
uring tape (Lufkin, Cooper Tools, Apex, NC, USA) was used
for measuring waist and hip circumferences to the nearest 0.1
cm and waist:hip ratio (WHR) was calculated by dividing waist
circumference by hip circumference. Skin folds were measured
using a John Bull
®
(British Indicators, London, UK) skin-fold
calliper to the nearest 0.1 mm of the triceps, sub-scapula, medial
calf, abdominal and supra-spinal skin folds. Landmarks were
drawn first where-after post-graduate biokinetics students with a
level 2 anthropometic qualification did the measurements.
The children’s body composition (percentage muscle and fat)
was measured by air-displacement plethysmography (BOD-POD,
Life Measurement Inc, Concord, CA), which was calibrated at the
start of each day’s measurements with a cylinder of standardised
volume. The BOD-POD system uses the principle of whole-body
densitometry to obtain the amount of fat and lean body mass in
the body. For accuracy of measurement, the subjects wore tight-
fitting clothing and a swimming cap, removed all jewellery and
emptied the bladder before testing. Minimal movement of the
subjects within the BOP-POD was ensured. The subjects were
shown how to use the thoracic gas volume tubes and a measure-
ment was taken to compensate for lung volume.
Body volume (litre) was measured with the BOD-POD, using
the ratio between pressure and volume, as explained by Boyle’s
law. The ratio is used to calculate the unknown volume by meas-
uring the pressure directly. The pressure in both chambers reacts
immediately and the difference in pressure represents the relative
volume of air in each chamber.
Body density (Db) was calculated by dividing the body’s
