Andersen LB, Riddoch C, Kriemler S, et al. Br J Sports Med (2011). doi:10.1136/bjsports-2011-090333
Copyright Article author (or their employer) 2011. Produced by BMJ Publishing Group Ltd under licence.
1 of 6
1Department of Exercise
Epidemiology, Center for
Research in Childhood Health,
University of Southern
Denmark, Odense, Denmark
2Department of Sports
Medicine, Norwegian School
of Sport Sciences, Oslo,
3Department for Health,
University of Bath, Bath, UK
4Swiss Tropical and Public
Health Institute, University of
Basel, Basel, Switzerland
5Griffi th University and Mater
Medical Research Institute,
Lars Bo Andersen, Department
of Exercise Epidemiology,
Center for Research in
Childhood Health, University of
Southern Denmark, Campusvej
55, 5230 Odense M, Denmark;
Accepted 20 June 2011
Physical activity and cardiovascular risk
factors in children
Lars Bo Andersen,1,2 Chris Riddoch,3 Susi Kriemler,4 Andrew Hills5
Background A number of recent systematic
reviews have resulted in changes in international
recommendations for children’s participation in physical
activity (PA) for health. The World Health Authority
(WHO) has recently released new recommendations.
The WHO still recommends 60 min of moderate to
vigorous physical activity (MVPA), but also emphasises
that these minutes should be on top of everyday
physical activities. Everyday physical activities total
around 30 min of MVPA in the quintile of the least active
children, which means that the new recommendations
constitute more activity in total compared with earlier
Objective To summarise evidence justifying new PA
recommendation for cardiovascular health in children.
Methods The results of recent systematic reviews are
discussed and supplemented with relevant literature not
included in these reviews. PubMed was searched for the
years 2006–2011 for additional topics not suffi ciently
covered by the reviews.
Results PA was associated with lower blood pressure
and a healthier lipid blood profi le in children. The
association was stronger when a composite risk factor
score was analysed, and the associations between
physical fi tness and cardiovascular disease (CVD)
risk factors were even stronger. Muscle strength and
endurance exercise each had an effect on blood lipids
and insulin sensitivity even if the effect was smaller for
muscle strength than for aerobic exercise. New evidence
suggests possible effects of PA on C-reactive protein.
Conclusion There is accumulating evidence that
PA can have benefi cial effects on the risk factors of
CVD in children. Public health policy to promote PA in
children, especially the most sedentary children, may be
a key element to prevent the onset of CVD later in the
This overview includes a consideration of lit-
erature published since 2005 summarising asso-
ciations between PA and cardiovascular disease
(CVD) risk factors in children. In 2005, Strong et al1
published a comprehensive systematic review of
the effects of physical activity (PA) on seven dif-
ferent health outcomes. The review identifi ed 850
articles, which included CVD risk factors such as
blood lipids, blood pressure and clustered CVD
risk factors. A number of studies reporting asso-
ciations with haemostatic factors and markers of
infl ammation were also included. Based on the
review, Strong et al recommended that children
should accumulate 60 min of moderate to vigor-
ous (MVPA) every day. This recommendation was
primarily based on a judgment of the amount of
PA included in different intervention studies. It is
important to note that none of the intervention
studies reported how active children were beside
the intervention, and despite that recommenda-
tions included information regarding total MVPA.
Moreover, few studies at that time had collected
objective measures of PA.
Since this review, studies have been published
where PA has been assessed objectively. Another
improvement has been to analyse a composite
score of CVD risk factors. These studies gener-
ally report stronger associations because CVD
risk factors tend to cluster in sedentary and obese
children. A further area of development has been
studies analysing the association between PA and
infl ammatory markers.
Previous recommendations for PA in children
have suggested a total of 60 min of MVPA per day.
However, our knowledge of total PA levels of chil-
dren has been limited, primarily because activ-
ity has been assessed by self report – a method
known to carry unacceptable levels of error in
terms of quantifying PA. The emergence of more
precise, objective methods of assessing activity
has greatly enhanced our understanding in this
fi eld. A further issue is that previous recommen-
dations have been based primarily on the results
of generally small intervention studies. However,
interventions generally do not take the PA of
daily living into account. They only quantify the
activity added to everyday living. This may have
caused an underestimation of the total PA neces-
sary to maintain cardiovascular health.
A further review by Janssen and LeBlanc2
updated the literature on PA and health. However,
due to the large number of studies in the area, they
limited their search to studies that reported out-
comes as dichotomous variables. Limiting studies
in this way effectively excludes most of the more
recent (and larger) studies that have used objective
measures of PA, because these studies have often
treated the outcome variables as continuous vari-
ables. We believe this to be a major limitation of
this review for two reasons. First, the studies util-
ising the more precise measurements of PA have
been omitted. Yet, their greater measurement pre-
cision probably gives their results greater valid-
ity and hence importance. Second, the process of
dichotomising outcome variables reduces power
and hence associations will tend to be weaker.
Furthermore, most of the CVD risk factors show
linear relationships with PA in adults.
The aim of this review is to summarise results
from the previous reviews of Strong et al1 and
Janssen et al,2 and to extend their fi ndings with
(1) studies relating objective measures of PA to
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CVD risk factors,3 (2) recent studies including infl ammatory
markers as outcomes and (3) studies analysing CVD risk using
composite – or ‘clustered’ – CVD risk scores.4
A PubMed search (2005–January 2011) was undertaken for
publications in English related to PA and individual biologi-
cal CVD risk factors in children (excluding obesity, which is
reported in a separate article). PubMed was then searched to
identify review articles. Additional articles were added from
reviews and reference lists from other articles with special
emphasis given to studies relating objective measures of PA
to cardiovascular risk factors. Finally, a search was conducted
to identify studies analysing composite risk factor scores for
CVD risk factors.
A meta-analysis from 2003 indicates no clear association
between PA and blood pressure in normotensive children,5
while there are some indications that prolonged programs can
lower blood pressure in hypertensive children. Some stud-
ies of children with systemic hypertension show a benefi cial
effect of aerobic activity programs of 12–32 week duration on
blood pressure,6–8 but an 8-week strength training program
by itself had no infl uence on blood pressure in hypertensive
children.9 10 The lack of effect of exercise on blood pressure
in this study may be related to the short duration of the train-
ing intervention, because interventions with longer duration
do fi nd a gradual increase in effect.8 Strength training after an
aerobic activity intervention has been shown to prevent the
return of blood pressure to preintervention levels in hyperten-
sive adolescents.11 12
Observational studies have found a dose–response associa-
tion between aerobic fi tness and blood pressure,13 14 but these
studies found no association between self-reported sports par-
ticipation and blood pressure. The inverse association between
aerobic fi tness and blood pressure was stronger in overweight
children.14 Associations between aerobic fi tness and hyper-
tension were moderate in magnitude with ORs for hyperten-
sion of 1.5–3.0 for the least fi t. In the study of Nielsen and
Andersen,14 risk was only elevated in the lowest quintile of
fi tness, but in the study of Andersen,13 an inverse, graded asso-
ciation between fi tness and blood pressure was observed from
a fi tness level below 50 and 45 ml/min/kg in boys and girls,
Experimental studies have almost entirely focused on chil-
dren with hypertension6 7 11 12 or obesity,8 15 16 and most studies
had small sample sizes. The two largest studies included 996
and 67 children, respectively.8 Hansen et al studied both normo-
tensive and hypertensive overweight children. They observed a
reduction in systolic and diastolic blood pressures in the train-
ing subgroups of 6.5 and 4.1 mm Hg, respectively, in the nor-
motensive group, and 4.9 and 3.8 mm Hg, respectively, in the
hypertensive group, after 8 months of training. Most interven-
tion studies have included between 60 and 180 min/week of
prescribed exercise. This equates to 9–30 min/day when aver-
aged over a week. Overall, the results from these intervention
studies were positive with reports of signifi cant reductions in
systolic blood pressure in response to aerobic exercise training,
with effect sizes in excess of 0.80.6–8 11 12 15–17 Three of the inter-
ventions including aerobic training also reported signifi cant
reductions (~6–11%) in diastolic blood pressure.8 11 15 Studies
that used training modalities other than aerobic exercise, such
as muscular resistance exercise, were less conclusive with small
to modest effect sizes being observed.2
In conclusion, these data suggest that a PA/exercise inter-
vention with a duration of at least 30 min, a frequency of 3
times/week and intensity suffi cient to improve aerobic fi tness
can be effective in reducing blood pressure in children with
In observational studies, associations between PA and total
cholesterol, high-density lipoprotein cholesterol (HDL-C),
low-density lipoprotein cholesterol (LDL-C) and triglyceride
levels are generally weak.18 Nevertheless, associations suggest
an overall benefi cial effect of PA on HDL-C and triglyceride
levels, but no consistent effect on total cholesterol or LDL-C
Dobbins et al19 published a Cochrane review in 2009 includ-
ing seven school-based randomised controlled trials (RCTs)
that included a measure of lipids as outcome measure in
response to a PA intervention. This review identifi ed seven
studies.20–26 Two further studies have been published since this
review.27 28 Overall, studies including clinical or school-based
trials (randomised and non-randomised) show a weak benefi -
cial effect on HDL-C and triglyceride levels, but no effect on
total cholesterol or LDL-C levels.29–31 School-based interven-
tions have generally not been effective in improving lipid and
lipoprotein levels, but many of these interventions have also
failed to increase PA or fi tness.24 32 In a recent 2-year school-
based intervention, which did increase physical fi tness, ben-
efi cial effects were also found on triglyceride (13% decrease)
and the ratio of total:HDL cholesterol (6% decrease).27 Similar
benefi cial changes in blood lipids were observed in a Swiss
school-based intervention.28 Benefi cial effects are usually seen
when the intervention is substantive enough to change aerobic
The review of Janssen and LeBlanc2 was limited to studies
with dichotomous outcomes. As discussed earlier, most obser-
vational studies report linear associations rather than risk of
hypercholesterolaemia. This is in contrast to blood pressure,
where the existence of hypertension as a dichotomised variable
is commonly used. Some of the observational studies contra-
dict fi ndings of the intervention studies that commonly report
that HDL rather than total cholesterol is associated with PA
or fi tness. Data from the European Youth Heart Study suggest
weak but highly signifi cant associations between objectively
measured PA and total cholesterol and triglyceride, but no
association with HDL.18 In the same project, triglyceride and
HDL have also been reported to be associated with indicators
of muscle fi tness such as handgrip strength, situps, muscular
endurance and a composite score of these tests.34
Intervention studies conducted outside school tend to
only include children with hypercholesterolaemia or obe-
sity. Janssen and LeBlanc2 included six RCTs and two non-
randomised interventions. Results from these studies are
mixed. The fi ve studies that were based on aerobic exercise
alone observed signifi cant improvements in at least one lipid/
lipoprotein variable. The interventions that were based on
resistance training35 and circuit training15 reported small and/
or insignifi cant changes for all of the lipid/lipoprotein variables
examined, and the effect sizes within these studies tended to
be quite small.
It appears that a minimum of 40 min of moderate activity
per day, 5 days per week for at least 4 months is required to
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PA and MetS, particularly in 15-year-old girls.49 They sug-
gested that the relationship was strongest because the 15-year-
old girls had the lowest levels of PA. Other studies from the
European Youth Heart Study measured PA levels with acceler-
ometry in 1730–2800 children aged 9 and 15 years and used a
z-score classifi cation for MetS.18 41 They found a graded asso-
ciation in MetS z-score through all PA percentiles. Of note,
accelerometry data suggested that MVPA had to be about 90
min/day to effectively reduce the risk of MetS.
Rizzo et al49 analysed a composite CVD risk factor score
against quartiles of fi tness and found strong associations in
both boys and girls. Further examination of these later studies
revealed a clear dose–response relation. A recent follow-up of
Copenhagen Schoolchild Intervention Study by Andersen et al
showed that the association between fi tness and MetS became
much stronger in the same children from 6 to 9 years of age.
The OR between upper and lower quintiles increased from
2 to 35 in this age span, and metabolic syndrome seemed to
develop after the age of 6 years. Janssen and LeBlanc reported
four studies that used direct measures of cardiorespiratory
fi tness.2 42 44 50 51 All reported strong and signifi cant relations
with MetS. The summary OR for the least fi t group relative to
the most fi t group in the four studies that measured fi tness was
6.79 (95% CI: 5.11 to 9.03). Several studies show improvement
in elements of the MetS in association with PA in obese and
non-obese children,15 35 52–55 but the amount of activity neces-
sary to prevent or treat the MetS is not specifi ed.
CVD risk factors and muscle fi tness
Few studies have examined the association of the muscular
endurance and strength with CVD risk factors among chil-
dren and adolescents.56–58 Two of these studies included
measurement of maximal strength only, and the associations
are only analysed with individual CVD risk factors and not
clustered metabolic risk.56 58 García-Artero et al57 measured
muscle endurance, explosive strength and maximal strength
and included a lipid-metabolic risk score in their analyses.
However, they did not directly measure cardiorespiratory fi t-
ness, and they could therefore not analyse whether there was
an association independent of aerobic fi tness. Only one study
has evaluated the association of both single and combined
muscle strength measurements with MetS risk independent of
aerobic fi tness.34 In this study, muscle fi tness was negatively
associated with clustered metabolic risk, independent of car-
diorespiratory fi tness, but the association was weaker than for
cardiorespiratory fi tness.
Other cardiovascular variables
Thomas and Williams and Thomas et al have conducted two
comprehensive reviews of studies of the effect of exercise on
C-reactive protein (CRP), interleukin 6 (IL-6) and fi brinogen.59 60
CRP is an acute-phase reactant that increases signifi cantly
in response to trauma and infl ammation. CRP is a sensitive
marker of infl ammation, and there is evidence of its causal
role in infl ammation.61 Age, sex, body mass index, adiposity,
physical inactivity, physical fi tness and smoking are associated
with CRP levels.62 There is evidence to suggest that regular PA
protects against disease associated with chronic low-grade sys-
temic infl ammation and decrease the level of CRP.63 The mech-
anisms responsible for the association between reduced CRP
and increased PA are unknown, partly because PA is related
to several confounders that are independently associated with
CRP concentration. Many researchers claim that PA mainly
achieve improvement in lipid and lipoprotein levels, primar-
ily increased HDL-C and decreased triglyceride levels.1 This
implies the need for a sustained amount of MVPA on a regu-
lar basis in order to induce and maintain a benefi cial effect.
Observational studies indicate a graded association between
amount of PA and blood lipid levels.
Clustered CVD risk
Metabolic syndrome (MetS) was fi rst described in adults,
but retrospective evaluation of paediatric data suggests that
MetS characteristics exist in 3–14% of the general population
of children and in 13–37% of obese children.36 Clustering of
CVD risk factors is based on the fact that CVD risk factors
are not independently distributed in the population but clus-
ter in some individuals. Although there appears to be consen-
sus regarding the risk factors for MetS in adults, there is no
consensus for the defi nition in children and adolescents. The
reason for the lack of consensus lies in the fact that children
do not routinely exhibit CVD; thus, it is diffi cult to relate the
criteria to a health outcome. The condition is therefore defi ned
as clustered CVD risk by some authors, while others still use
MetS, even if defi nitions differ between authors. In addition,
in early stages of insulin resistance, fasting blood glucose is
not elevated, because the resistance is compensated by a large
increase in insulin production. Fasting glucose is therefore a
problematic component of the MetS in children. A number of
suggestions for defi ning cutoff points for MetS in children have
been published.37–39 Alternatively, composite scores based on
the sum of percentile ranking and sum of sex- and age-specifi c
z-scores have also been used.18 40–42 The different CVD risk
factors usually included in the defi nitions are waist circumfer-
ence (or BMI), triglycerides, blood pressure, fasting glucose and
reduced HDL-C level. It would make sense to include physical
fi tness as part of the score, as it is diffi cult to fi nd a rationale for
including measures of fatness but not fi tness, considering that
both these conditions are strongly associated with clustering
of other CVD risk factors such as insulin resistance, blood lip-
ids and blood pressure.
Studies relating self-reported PA to MetS are inconclusive.
Pan and Pratt43 used the PA section of the NHANES 1999–2002
questionnaire and found no signifi cant relationship between
PA and MetS in 4450 adolescents aged 12–19 years. Andersen
et al44 also reported no association between self-reported PA
and MetS in 305 children participating in the Danish Youth
and Sport Study. Conversely, Moore et al,45 using the Youth
Risk Behavior Surveillance, found that those children report-
ing low PA had three times the risk of MetS compared with
children with high PA levels. McMurray et al46, also using a
validated questionnaire, found that children who developed
MetS as adolescents had 22% lower PA scores than those chil-
dren who did not develop MetS. Kelishadi et al,47 also using a
PA questionnaire in 4811 adolescents aged 6–18 years, found a
small difference in the overall rate of MetS between tertiles of
PA. Children with low PA levels were 1.6–1.8 times more likely
to have MetS. In the review of Janssen and LeBlanc,2 the sum-
mary OR for the least active group relative to the most active
group was 1.68 for self-reported PA (95% CI: 1.22 to 2.31).
The fi ndings of a relationship between PA and MetS have
been more consistent when accelerometry was used to esti-
mate PA. Brage et al48 determined the relationship between
accelerometer-measured PA and MetS z-score in 389 Danish
children. They found a graded negative association between
PA levels and MetS z-score. A study of 529 Swedish children
aged 9 and 15 years also found an inverse relationship between
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affects health through its relation to fatness. However, if PA
causes changes in fat tissue, which produces cytokines affect-
ing CRP, PA remains the primary cause of the change.
Studies reporting the association between PA and CRP
concentration in young people are relatively scant, with
much of the research concentrating on overweight and obese
Observational studies have shown associations between PA
and CRP.64 65 Other studies using self-reported PA have failed
to fi nd an association with CRP.66–69 When physical fi tness
is analysed, studies fi nd much stronger associations to CRP.
Andersen et al found an association between cardiorespiratory
fi tness and CRP of –0.49 in 9-year-old children. They further
found an 11.3 times higher risk for CVD risk factors to cluster
in the upper quartile of CRP compared with the lower quartile.
The reason why PA shows a weaker association with CRP
than fi tness could be that only high-intensity aerobic exercise
may have an effect. Alternatively, it could be the fact that PA is
assessed with higher levels of error.
Most intervention studies only include obese children, and
many of them have small sample size. Interventions including
PA or PA and diet lasting 4–6 months have found reduction in
CRP in obese adolescents.55 70 71 Change in CRP was indepen-
dent of weight. Conversely, Nassis et al72 found no reduction
in CRP in a study of obese girls although cardiorespiratory fi t-
ness increased by 18.8%. Lack of effect on CRP was also found
in two studies of obese children by Barbeau et al73 and Kelly
et al,74 but the latter study only included nine subjects, and the
small sample size may have caused a statistical type 2 error.
The role of exercise on other infl ammatory markers is
controversial. Hotamisligil et al75 observed that adipose tis-
sue from obese mice was producing tumour necrosis factor
α (TNFα), a proinfl ammatory marker, and this cytokine was
responsible for insulin resistance. This observation changed
our view on adipose tissue, and it has become apparent that
obesity is linked to a state of chronic infl ammation. Obesity
results not only in the secretion of TNFα, but induces the
release of many cytokines including resistin, IL-1 and IL-6.
Given this proinfl ammatory response and the observation
that systemic IL-6 concentrations are elevated in obesity, it
is generally thought that elevations in IL-6 have a negative
effect on metabolism.76 However, it is now proven that mus-
cle cells also act as an endocrine organ, and among other sub-
stances produce IL-6 during contraction.77 Myokines, which
are cytokines produced by the muscle cells, may be involved
in mediating the health benefi cial effects of exercise and play
important roles in the protection against diseases associated
with low-grade infl ammation, insulin resistance, hyperlipi-
daemia such as CVDs, type 2 diabetes and cancer. IL-6 pro-
duced by the muscle enhances glucose uptake in the muscle
cells, glucose production from the liver and lipolysis in the
adipose tissue. Training studies have shown that adaptation
to training reduces IL-6 response in plasma. However, even
if plasma-IL-6 appears to be downregulated by training, the
muscular expression of the IL-6 receptor appears to be upreg-
ulated.77 How these observations apply to children is not
known. Furthermore, it is diffi cult to evaluate the role of IL-6
in observational studies, because the acute response to exer-
cise disappears fast, and fasting blood samples may therefore
not be suitable.78 Most intervention studies are conducted in
obese children. A decrease in IL-6 has been found in obese
children after an exercise intervention,70 but it has also been
seen in normal weight children.71 Currently, there is no con-
sensus of the effect of PA on infl ammation in children.
Cardiovascular fi tness (aerobic fi tness)
Correlational studies indicate low-to-moderate positive rela-
tionships between PA and both maximal and submaximal
indicators of aerobic fi tness. The strength of the association
depends on how accurately PA and to some degree aerobic fi t-
ness are assessed. Dencker and Andersen3 reviewed studies
using objectively measured PA in children. The objective data
from these studies strongly suggest that the amount of PA in
childhood is weakly associated with aerobic fi tness with r val-
ues of 0.25–0.40.
Experimental training studies with children aged 8 years and
older indicate improvements in aerobic fi tness.24 28 30 32 79–81
Some intervention studies have used high-intensity aerobic
sports, but it is interesting that differences in fi tness were also
found in relation to everyday activities such as cycling to school,
and the differences seem not to be caused by selection.82–85
Programs involving continuous vigorous activity for >30 min at
least 3 days per week result in an approximately 10% increase
in fi tness (3–4 ml/kg/min). However, cycling to school, which
is a PA repeated twice a day, results in 8–9% change in aerobic
PA recommendations in relation to metabolic health in chil-
dren have changed since the fi rst recommendation was for-
mulated by the American College of Sports Medicine in
1988.86 PA was focused on aerobic exercise performed at an
intensity suffi cient to increase aerobic fi tness. This has gradu-
ally changed, and emphasis is now placed on both aerobic
and resistance exercise. The change in recommendations is
based on the evidence of an independent association between
muscle fi tness and metabolic disorders. Another change was
related to the quantity of recommended exercise. Since the
recommendations published in the late 1990s by Biddle et al,87
most authorities have recommended 60 min of at least mod-
erate-intensity PA accumulated most days as the main goal.
WHO’s latest Global Guidelines recommend that 60 min of
at least moderate intensity should be accumulated on top of
activities of daily living.88 Studies using accelerometry have
shown that even the most sedentary children accumulate to
around 30–40 min of MVPA per day.18 This change is there-
fore a major increase in recommended PA level in children.
The change is logical, because earlier evidence was based pri-
marily on intervention studies and self-reported PA in obser-
vational studies. Intervention studies describe the content of
the intervention, but there is usually no knowledge of what
PA participants participated in outside the intervention. Two
factors have increased our understanding in this area. These
are a better quantifi cation of PA by accelerometry and a more
accurate defi nition of metabolic outcomes. The introduction
of a composite CVD risk factor score based on continuous
z-scores has improved associations between exposure and
outcome, which makes it possible to better quantify the
amount and type of PA children need to improve health.
Development of methods to assess PA objectively can still
be improved. There is still no consensus on how to assess PA
in children and adolescents reliably regarding the appropriate
time period representative for overall PA and the infl ation fac-
tor that should be used to account for the behavioural variation
of PA in youth. Other limitations of accelerometry are related
to the lack of ability to quantify cycling and swimming. These
limitations may soon be overcome, because much research
is focused on combining different measures such as acceler-
ometry, heart rate, cycle computers and global positioning
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system. Metabolic outcome measures can also be improved.
Dichotomisation of metabolic variables has mainly been used
to help physicians decide when drug treatment was justifi ed,
but treatment of children with metabolic disorders will prob-
ably mainly be based on lifestyle changes in the future except
for children having specifi c genetic problems such as familiar
hypercholesterolaemia. Therefore, it makes sense to use con-
tinuous scores to defi ne metabolic health. Despite all these
limitations, we believe that the current 2010 WHO recom-
mendation is based on solid evidence.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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published online July 26, 2011Br J Sports Med
Lars Bo Andersen, Chris Riddoch, Susi Kriemler, et al.
factors in children
Physical activity and cardiovascular risk
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