CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 6, November/December 2010
AFRICA
309
Editorial
Associations of serum C-reactive protein with physical
activity, fitness and fatness in South African adolescents
Globally the prevalence of overweight is increasing signifi-
cantly, not only in economically developed regions, but also
in developing countries. In South Africa, the prevalence of
combined overweight and obesity among high-school children
increased from 21.2% in 2002
1
to 25% in 2008,
2
with 35% of
high-school girls being overweight or obese.
2
The metabolic syndrome (MS) is a cluster of biological
markers that together predict the development of cardiovascular
disease and type 2 diabetes. These markers are hypertension,
insulin resistance, central adiposity, hypertriglyceridaemia and
decreased high-density lipoprotein cholesterol (HDL-C). The
MS is now increasingly emerging among children and adoles-
cents.
3
Low-grade systemic inflammation is proposed as a
significant component of the MS.
4
C-reactive protein (CRP) is secreted by the liver and adipose
tissue in response to infections and inflammatory conditions.
5
Levels of CRP decrease during the early convalescent phase and
are usually low in healthy subjects. In the absence of infection,
low-grade inflammation characterised by serum CRP levels of
between 1 and 10 mg/l are associated with an increased risk of
the development of cardiovascular disease.
6
Serum CRP concen-
trations in this range can be detected using high-sensitivity
methods and are generally referred to as high-sensitivity CRP
(hsCRP).
6
Although the MS has been described in paediatric populations
from many different countries, limited evidence on the MS and
risk for cardiovascular disease among South African children is
available.
7-9
Studies on blood lipid levels of South African chil-
dren without familial hyperlipidaemia are scarce, but published
data indicate very little evidence of hypertriglyceridaemia
and decreased HDL-C among black South African children.
8
However, South African studies indicate a positive association
between overweight in children and increased blood pressure,
9
plasminogen activator inhibitor-1 activity, plasma fibrinogen
and the thrombin–anti-thrombin complex,
10
as well as higher
fasting plasma insulin possibly increasing the risk for future
cardiovascular disease.
7,9
Increased adiposity has been associated with higher serum
CRP concentrations in US children aged three to 16 years
from the National Health and Nutrition Examination survey
(NHANES) 1999–2004.
11
In a review of research linking obesity
and low-grade inflammation in children, a significant posi-
tive correlation between body mass index (BMI) and CRP was
confirmed.
12
Ruiz
et al
.
13
found a significant positive association
between body fat, derived from five skin folds, and serum CRP
in Swedish children, aged nine to 10 years.
Other variables describing body composition were investi-
gated with regard to their power to predict low-grade inflam-
mation in Caucasian adolescents. Although waist circumference
and waist:height ratio showed a significant, positive predictive
power to detect elevated serum CRP, BMI was the best predictor
of elevated serum CRP levels in these adolescents.
14
Abdominal
obesity in children was also associated with higher serum CRP
concentrations in Norwegian children, nine and 15 years old. In
the same study, serum CRP was positively associated with blood
pressure, blood glucose, insulin and triglyceride concentrations.
15
In a study of asymptomatic European adolescents, serum hsCRP
was also associated with risk for cardiovascular disease. No
lifestyle factors showed an association with cardiovascular risk
in this study.
16
These results confirm the value of elevated serum
hsCRP as an early marker for cardiovascular disease in older
children and adolescents.
15,16
Ridker
17
reviewed large-scale prospective studies that showed
hsCRP is an independent predictor of future cardiovascular
events, as well as of hypertension and type 2 diabetes mellitus.
Studies in animal models suggest, however, that hsCRP may not
promote atherosclerosis directly, but only serve as a marker of
vascular inflammation.
18
Recently Ridker reviewed the evidence
from retrospective as well as primary-prevention trials and
found that hsCRP was the strongest predictor of risk of vascu-
lar events.
19
A meta-analysis of 54 prospective cohort studies
identified and confirmed CRP as an independent risk marker for
cardiovascular disease.
20
A cross-sectional study in Swedish children nine to 10 years
old showed a significant negative association between cardio-
vascular fitness, measured by ergometer bike test, and CRP. No
association between physical activity measured by accelerome-
try and CRP could be found, although physical activity was posi-
tively associated with cardiovascular fitness. After controlling
for body fat, serum CRP was no longer negatively associated
with cardiovascular fitness. The influence of fatness on serum
CRP in these children was greater than the influence of fitness.
The results suggest that the beneficial effects of physical
activity on low-grade inflammation may be mediated through
the association with cardiovascular fitness, but that excessive
fatness may decrease the beneficial effects of physical activity
in children.
13
Interventions resulting in about a 5% weight loss in
obese children resulted in a decrease in serum CRP concentra-
tions.
12
Apparently, overweight and obesity in children have a
stronger association with serum CRP than physical activity, but
physical activity may help to prevent excessive body fat accu-
mulation in children and may even result in moderate fat loss in
obese children.
Most studies of body composition, physical activity and low-
grade inflammation in children have been done in Caucasian
populations. Longitudinal studies in larger cohorts of different
age groups and ethnic backgrounds are needed. Further research
is also necessary to assess the changes and effects of other
