CONTEXT:

The effects of school-based physical activity (PA) programs on different cardiometabolic risk factors and the most appropriate features of PA programs to achieve maximum effectiveness are unclear.

OBJECTIVE:

To provide a comprehensive synthesis of the effectiveness of school-based PA interventions on cardiometabolic risk factors in children.

DATA SOURCES:

We identified studies from database inception to February 22, 2018.

STUDY SELECTION:

We selected studies that were focused on examining the effect of school-based PA interventions on cardiometabolic risk factors in children.

DATA EXTRACTION:

Random-effects models were used to calculate the pooled effect size (ES) for the included cardiometabolic risk factors (waist circumference [WC], triglycerides, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, systolic blood pressure and diastolic blood pressure (DBP), and fasting insulin and glucose).

RESULTS:

Nineteen randomized controlled trials (which included 11 988 children aged 3–12 years) were included in the meta-analysis. School-based PA programs were associated with a significant small improvement in WC (ES = −0.14; 95% confidence interval [CI]: −0.22 to −0.07; P < .001), DBP (ES = −0.21; 95% CI: −0.42 to −0.01; P = .040), and fasting insulin (ES = −0.12; 95% CI: −0.20 to −0.04; P = .003).

LIMITATIONS:

Authors of few studies described the implementation conditions of their interventions in detail, and compliance rates were lacking in most studies. In addition, results by sex were provided in a small number of studies.

CONCLUSIONS:

School-based PA interventions improve some cardiometabolic risk factors in children, such as WC, DBP, and fasting insulin.

The most recognized cardiometabolic risk factors in children are waist circumference (WC), triglycerides, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), blood pressure (BP), insulin, and glucose.1,2 Additionally, obesity frequently clusters with other cardiometabolic risk factors, including dyslipidemia, elevated BP, and insulin resistance, in some children and adolescents.3 Consistent evidence supports that these individuals are more prone to cardiovascular disease events than those with a single cardiovascular disease risk factor.

Because children spend a majority of their waking hours sitting at school, this setting is appropriate for the implementation of preventive interventions, particularly those that include activities promoting physical activity (PA).4 Thus, most interventions that are focused on improving children’s cardiometabolic risk factors are conducted in the school setting.

Although evidence regarding the benefits of PA on the cardiometabolic risk profile of children is accumulating,5,6 several recent meta-analyses have revealed controversial results regarding the effectiveness of school-based PA interventions on the improvement of the cardiometabolic profile, such as on obesity,7,9 BP,10 or both the BMI and BP.11 Two published meta-analyses synthetized the effectiveness of school-based PAs on some cardiovascular markers,12,13 but a comprehensive review and meta-analysis that includes insulin resistance indicators is lacking. In addition, several studies in which the authors test the effectiveness of school-based PA interventions on cardiometabolic risk factors have been published recently.

This meta-analysis was focused on providing a comprehensive synthesis of the effectiveness of school-based PA interventions on cardiometabolic risk factors in children.

This meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement,14 and we followed the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions.15 This meta-analysis was registered with the PROSPERO International prospective register of systematic reviews database (CRD42018082416).

Studies were identified in 6 databases (Web of Science, Embase, SPORTDiscus, Cochrane Library, Medline [via PubMed], and the Cumulative Index to Nursing and Allied Health Literature) from inception to February 22, 2018. We also manually scanned the reference lists of the published full-text articles and systematic reviews for relevant studies. The search strategy applied was (“school-based” AND (“physical activity” OR exercise) AND (program OR intervention) AND (“blood pressure” OR triglyceride OR lipids OR cholesterol OR “waist circumference” OR “glycaemia” OR “glucose” OR “insulin” OR “cardiometabolic risk factors” OR “metabolic syndrome”) AND child* AND “randomized controlled trial”). Studies were limited to those published in Spanish and English. The included articles were randomized controlled trials (RCTs) in which the authors assessed the effectiveness of school-based PA interventions on the following cardiometabolic risk factors: WC, fasting insulin, fasting glucose, TC, triglycerides, HDL-c, low-density lipoprotein cholesterol (LDL-c), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP).

Two reviewers (D.P.P.-C. and I.C.-R.) independently evaluated the titles and abstracts for eligibility. Duplicate studies and irrelevant titles and abstracts were removed; then the 2 reviewers independently retrieved the potential candidate full-text articles for further evaluation. Disagreements were resolved by consensus between them; if disagreement persisted, a third reviewer solved the conflict (V.M.-V.). When a study published multiple reports, we included the article in which the sample size was largest. The reviewers were not blinded to the authors, journals, or institutions.

The inclusion criteria were as follows: (1) population, healthy preschool-aged children and schoolchildren aged 3 to 12 years; (2) type of study, RCT in which the control group (CG) did not receive any PA intervention; (3) type of intervention, school-based PA program that included additional PA time; and (4) primary outcome, changes in the levels of any of the cardiometabolic risk factors (WC, SBP, DBP, MAP, fasting insulin, fasting glucose, TC, triglycerides, HDL-c, and LDL-c) between the baseline and the end of the PA intervention. No restrictions on the frequency, duration, or type of PA were made. When the studies had several groups in which PA was applied exclusively or in combination with a nutritional intervention, we selected the group in which PA was applied exclusively as the intervention group (IG).

The exclusion criteria were as follows: (1) studies developed with children and adolescents in which the results were presented jointly and were not stratified according to age ranges, (2) studies not written in Spanish or English, (3) studies in which the interventions consisted only of a PA educational component, (4) studies that included selected groups of children (such as children who were obese, overweight, or with physical or mental disorders), and (5) studies with inconsistent or insufficient data.

Two authors (D.P.P.-C. and I.C.-R.) independently reviewed each published study and extracted the following data: (1) first author’s name, (2) year of publication, (3) participant characteristics (number, age, and country), (4) study aim, (5) intervention features (type, duration, frequency, and intensity of PA), and (6) the means and SDs of cardiometabolic risks factors in the CG and IG and at the beginning and end of the PA program.

The methodologic quality of the studies was assessed by using the Cochrane Collaboration’s tool for assessment of the risk of bias.16 This tool is used to evaluate the risk of bias according to 6 domains: selection bias (random sequence generation and allocation concealment), performance bias (blinding of participants and personnel), detection bias (blinding of outcome assessment), attrition bias (incomplete outcome data), reporting bias (selecting reporting), and other bias. In this quality assessment tool, each domain can be considered low risk, unclear risk, and high risk of bias.

The effect size (ES) of each study was calculated as the standardized mean differences in the WC, SBP, DBP, MAP, fasting insulin, fasting glucose, TC, triglycerides, HDL-c, and LDL-c by using Cohen’s d index as the ES statistic. The ESs of the cardiometabolic risk factors from pre- to postintervention between groups (PA intervention versus control)17 in each study were calculated and pooled by using a random-effects model (DerSimonian-Laird approach). Finally, the ESs of all included studies were combined to estimate an overall summary ES with a 95% confidence interval (CI) and a random-effects model.

Cohen’s d categories were used to interpret the magnitude of the ES as follows: small, 0 ≤ |d| ≤ 0.5; medium, 0.5 < |d| ≤ 0.8; and large, |d| > 0.8.18 Negative ES values indicate a decrease in the cardiovascular risk factor level in favor of the IG over the CG except for HDL-c, for which a positive ES value indicates an improvement in this cardiometabolic risk factor in favor of the IG over the CG.

Study heterogeneity was assessed by using the I2 statistic, and the following values were used for interpretation: 0% to 40%, might not be important; 30% to 60%, moderate heterogeneity; 50% to 90%, substantial heterogeneity; and 75% to 100%, considerable heterogeneity. The corresponding P values were also taken into account.15 

To analyze the influence of each study on the overall ES, a sensitivity analysis was conducted. For this purpose, each study was deleted from the model, and the pooled analysis was recalculated.

A meta-regression analysis was used to assess the relationship between ES estimates and each of the following variables: age at baseline, duration of intervention sessions, frequency, and total program duration of each study included in the meta-analysis. The PA intensity was reported as a categorical variable, and a subgroup analysis was conducted to assess whether the intensity of the PA sessions influenced the overall ES.

Finally, visual inspection of funnel plots and the Egger’s test were conducted to detect publication bias.19 

The statistical analyses were performed by using the Stata SE software version 14 (Stata Corp, College Station, TX).

In the electronic search, we retrieved 2305 studies, of which 724 were excluded as duplicates. When the titles and abstracts were screened, 88 studies remained as potentially relevant and were reviewed for evaluation of the full text. The different steps in the selection process and the reasons for excluding 69 of the full-text articles are shown in Fig 1. Finally, 19 RCTs were included in this meta-analysis.20,38 

FIGURE 1

Literature search: PRISMA consort diagram. CINAHL, Cumulative Index to Nursing and Allied Health Literature; WOS, Web of Science.

FIGURE 1

Literature search: PRISMA consort diagram. CINAHL, Cumulative Index to Nursing and Allied Health Literature; WOS, Web of Science.

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In Table 1, the study characteristics are summarized, including the number of participants, the country, characteristics of PA interventions, and outcome measures reported in each study. All included studies were published between 1995 and 2018. The total sample included 11 988 children (6048 in the IG and 5940 in the CG) aged 3 to 12 years. All studies were school based and included boys and girls. The participants in 2 articles21,31 were preschool-aged children (3–5 years old; n = 675), and the remaining participants were schoolchildren (6–12 years old; n = 11 313).

TABLE 1

Characteristics of Studies Included in the Meta-analysis

Author, Year PublishedCountryNAge at Baseline, y, MeanSchool Grades Included at BaselineType of InterventionProgram DurationOutcome Measures
IGCG
Adab et al,20 2018 United Kingdom IG: 513; CG: 587 6.3 Second grade 30 min of PA per d, in bouts of >5 min with education about PA and nutrition; PA intensity: moderate to vigorous Normal health-related activities except PA and nutrition 12 mo SBP (millimeters of mercury) and DBP (millimeters of mercury) 
Tan et al,21 2017 China IG: 52; CG: 52 5.1 Third grade and preschool 60 min of PA 5 d/wk with a shared PA component as a control; PA intensity: moderate Normal PA habit 10 wk WC (centimeters), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Xu et al,22 2017 China IG: 605; CG: 466 9.2 First to fifth grades 10-min activity breaks twice daily with education about PA; PA intensity: moderate Not reported 12 mo WC (centimeters), TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), insulin (milliunits per liter), glucose (millimoles per liter), and triglycerides (millimoles per liter) 
Nogueira et al,23 2017 Australia IG: 155; CG: 85 10.6 N/A 10 min of aerobic and impact exercises 3 times weekly; PA intensity: vigorous Usual school physical activities 9 mo WC (centimeters) and MAP (millimeters of mercury) 
Muros et al,24 2015 Spain IG: 28; CG: 41 10.6 N/A 60 min of PA twice weekly; PA intensity: vigorous No intervention 6 mo WC (centimeters), TC (milligrams per deciliter), LDL-c (milligrams per deciliter), HDL-c (milligrams per deciliter), triglycerides (milligrams per deciliter), glucose (milligrams per deciliter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Hrafnkelsson et al,25 2014 Iceland IG: 128; CG: 139 7.3 Second grade 30–60 min of PA per d with nutrition education and a shared PA component as a control; PA intensity: moderate to vigorous 2 compulsory 40-min physical education lessons per wk 24 mo TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), insulin (milliunits per liter), glucose (millimoles per liter), triglyceride (millimoles per liter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Martínez-Vizcaíno et al,26 2014 Spain IG: 420; CG: 492 9.4 Fourth and fifth grade 90 min of PA sessions twice on weekdays and 1 150-min PA session on Saturday; PA intensity: moderate to vigorous The regular school schedule (2 h/wk of physical education classes) 9 mo WC (centimeters), LDL-c (milligrams per deciliter), insulin (microunit per milliliter), MAP (millimeters of mercury), and triglycerides and HDL-c (milligrams per deciliter) 
Siegrist et al,27 2013 Germany IG: 425; CG: 297 8.4 Second and third grade 45 min/mo of PA lessons with shared 2–3 physical education lessons as controls; 10 health-related lessons on nutrition, fitness, etc; PA intensity: vigorous The regular school schedule: 2–3 physical education lessons 12 mo WC (centimeters) 
Yin et al,28 2012 United States IG: 195; CG: 205 8.7 Third grade 80 min of PA with 40 min for snacks and teacher-assisted homework 5 d/wk with a shared PA component as a control; PA intensity: vigorous Not reported. 33 mo WC (centimeters), SBP (millimeters of mercury), DBP (millimeters of mercury), and TC/HDL-c ratio 
Thivel et al,29 2011 France IG: 229; CG: 228 6–10 First and second grades 60 min of PA twice weekly with a shared PA component as a control; PA intensity: N/A The regular school schedule (2 h/wk of physical education classes) 6 mo WC (centimeters) 
Jansen et al,30 2011 Netherlands IG: 985; CG: 1163 9.3 Third to eighth grade 40 min of physical education sessions 3 d/wk; sports and play outside school hours; 3 lessons on healthy nutrition; PA intensity: N/A 40-min physical education session 2 d/wk. 10 mo WC (centimeter) 
Puder et al,31 2011 Switzerland IG: 315; CG: 277 5.2 Preschool 45-min sessions of PA 4 d/wk; 22 sessions on healthy nutrition, media use, and sleep; PA intensity: N/A Regular school curriculum: 1 45-min PA lesson per wk. 10 mo WC (centimeters) 
Salcedo Aguilar et al,32 2010 Spain IG: 375; CG: 448 9.4 Fourth and fifth grade 90 min of PA 3 d/wk with a shared PA component as a control; PA intensity: moderate The regular school schedule (3 h/wk of physical education classes) 24 mo SBP (millimeters of mercury), DBP (millimeters of mercury), TC (milligrams per deciliter), and triglycerides (milligrams per deciliter) 
Kriemler et al,33 2010 Switzerland IG: 297; CG: 205 First and fifth grade 45 min, 2 additional physical education per wk with a shared PA component as a control; 3–5 short activity breaks (2–5 min each) during academic lessons; 10-min daily PA homework; PA intensity: moderate to vigorous 45 min, 3 compulsory weekly physical education lessons 12 mo WC (centimeters), SBP (millimeters of mercury), DBP (millimeters of mercury), HDL-c (millimoles per liter), triglycerides (millimoles per liter), and glucose (millimoles per liter) 
Walther et al,34 2009 Germany IG: 106; CG: 68 11.1 Sixth grade 45 min of PA with at least 15 min of endurance training per school d; PA intensity: N/A 45 min, 2 mandatory units of exercise per wk 12 mo TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), triglycerides (millimoles per liter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Reed et al,35 2008 Canada IG: 156; CG: 81 10 Fourth and fifth grade 15 min of PA per d 5 d/wk with a shared PA component as a control; PA intensity: moderate to vigorous 40-min physical education classes 2 d/wk 16 mo SBP (millimeters of mercury), DBP (millimeters of mercury), TC/HDL-c ratio, TC (millimoles per liter), LDL-c (millimoles per liter) 
Manios et al,36 1998 Greece IG: 288; CG: 183 6.5 First grade 45 min of practical physical education 2 d/wk with a shared PA component as a control; 4–6 h of theoretical physical education per y; 13–17 h of health and nutrition education; PA intensity: moderate The regular preschool schedule without health or physical education intervention 36 mo TC (milligrams per deciliter), LDL-c (milligrams per deciliter), HDL-c (milligrams per deciliter), triglycerides (milligrams per deciliter) 
Harrell et al,37 1996 United States IG: 588; CG: 686 9.5 Third and fourth grade Warm-up with 20 min of PA and cooldown 3 d/wk; classes on nutrition and smoking twice weekly; PA intensity: moderate No intervention 8 wk SBP (millimeters of mercury), DBP (millimeters of mercury), and TC (milligrams per deciliter) 
Vandongen et al,38 1995 Australia IG: 158; CG: 145 11 N/A 15 of min PA every school d with 6 30-min classroom PA lessons; PA intensity: moderate to vigorous No nutritional or physical fitness programs 9 mo SBP (millimeters of mercury), DBP (millimeters of mercury), and TC (millimoles per liter) 
Author, Year PublishedCountryNAge at Baseline, y, MeanSchool Grades Included at BaselineType of InterventionProgram DurationOutcome Measures
IGCG
Adab et al,20 2018 United Kingdom IG: 513; CG: 587 6.3 Second grade 30 min of PA per d, in bouts of >5 min with education about PA and nutrition; PA intensity: moderate to vigorous Normal health-related activities except PA and nutrition 12 mo SBP (millimeters of mercury) and DBP (millimeters of mercury) 
Tan et al,21 2017 China IG: 52; CG: 52 5.1 Third grade and preschool 60 min of PA 5 d/wk with a shared PA component as a control; PA intensity: moderate Normal PA habit 10 wk WC (centimeters), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Xu et al,22 2017 China IG: 605; CG: 466 9.2 First to fifth grades 10-min activity breaks twice daily with education about PA; PA intensity: moderate Not reported 12 mo WC (centimeters), TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), insulin (milliunits per liter), glucose (millimoles per liter), and triglycerides (millimoles per liter) 
Nogueira et al,23 2017 Australia IG: 155; CG: 85 10.6 N/A 10 min of aerobic and impact exercises 3 times weekly; PA intensity: vigorous Usual school physical activities 9 mo WC (centimeters) and MAP (millimeters of mercury) 
Muros et al,24 2015 Spain IG: 28; CG: 41 10.6 N/A 60 min of PA twice weekly; PA intensity: vigorous No intervention 6 mo WC (centimeters), TC (milligrams per deciliter), LDL-c (milligrams per deciliter), HDL-c (milligrams per deciliter), triglycerides (milligrams per deciliter), glucose (milligrams per deciliter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Hrafnkelsson et al,25 2014 Iceland IG: 128; CG: 139 7.3 Second grade 30–60 min of PA per d with nutrition education and a shared PA component as a control; PA intensity: moderate to vigorous 2 compulsory 40-min physical education lessons per wk 24 mo TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), insulin (milliunits per liter), glucose (millimoles per liter), triglyceride (millimoles per liter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Martínez-Vizcaíno et al,26 2014 Spain IG: 420; CG: 492 9.4 Fourth and fifth grade 90 min of PA sessions twice on weekdays and 1 150-min PA session on Saturday; PA intensity: moderate to vigorous The regular school schedule (2 h/wk of physical education classes) 9 mo WC (centimeters), LDL-c (milligrams per deciliter), insulin (microunit per milliliter), MAP (millimeters of mercury), and triglycerides and HDL-c (milligrams per deciliter) 
Siegrist et al,27 2013 Germany IG: 425; CG: 297 8.4 Second and third grade 45 min/mo of PA lessons with shared 2–3 physical education lessons as controls; 10 health-related lessons on nutrition, fitness, etc; PA intensity: vigorous The regular school schedule: 2–3 physical education lessons 12 mo WC (centimeters) 
Yin et al,28 2012 United States IG: 195; CG: 205 8.7 Third grade 80 min of PA with 40 min for snacks and teacher-assisted homework 5 d/wk with a shared PA component as a control; PA intensity: vigorous Not reported. 33 mo WC (centimeters), SBP (millimeters of mercury), DBP (millimeters of mercury), and TC/HDL-c ratio 
Thivel et al,29 2011 France IG: 229; CG: 228 6–10 First and second grades 60 min of PA twice weekly with a shared PA component as a control; PA intensity: N/A The regular school schedule (2 h/wk of physical education classes) 6 mo WC (centimeters) 
Jansen et al,30 2011 Netherlands IG: 985; CG: 1163 9.3 Third to eighth grade 40 min of physical education sessions 3 d/wk; sports and play outside school hours; 3 lessons on healthy nutrition; PA intensity: N/A 40-min physical education session 2 d/wk. 10 mo WC (centimeter) 
Puder et al,31 2011 Switzerland IG: 315; CG: 277 5.2 Preschool 45-min sessions of PA 4 d/wk; 22 sessions on healthy nutrition, media use, and sleep; PA intensity: N/A Regular school curriculum: 1 45-min PA lesson per wk. 10 mo WC (centimeters) 
Salcedo Aguilar et al,32 2010 Spain IG: 375; CG: 448 9.4 Fourth and fifth grade 90 min of PA 3 d/wk with a shared PA component as a control; PA intensity: moderate The regular school schedule (3 h/wk of physical education classes) 24 mo SBP (millimeters of mercury), DBP (millimeters of mercury), TC (milligrams per deciliter), and triglycerides (milligrams per deciliter) 
Kriemler et al,33 2010 Switzerland IG: 297; CG: 205 First and fifth grade 45 min, 2 additional physical education per wk with a shared PA component as a control; 3–5 short activity breaks (2–5 min each) during academic lessons; 10-min daily PA homework; PA intensity: moderate to vigorous 45 min, 3 compulsory weekly physical education lessons 12 mo WC (centimeters), SBP (millimeters of mercury), DBP (millimeters of mercury), HDL-c (millimoles per liter), triglycerides (millimoles per liter), and glucose (millimoles per liter) 
Walther et al,34 2009 Germany IG: 106; CG: 68 11.1 Sixth grade 45 min of PA with at least 15 min of endurance training per school d; PA intensity: N/A 45 min, 2 mandatory units of exercise per wk 12 mo TC (millimoles per liter), LDL-c (millimoles per liter), HDL-c (millimoles per liter), triglycerides (millimoles per liter), SBP (millimeters of mercury), and DBP (millimeters of mercury) 
Reed et al,35 2008 Canada IG: 156; CG: 81 10 Fourth and fifth grade 15 min of PA per d 5 d/wk with a shared PA component as a control; PA intensity: moderate to vigorous 40-min physical education classes 2 d/wk 16 mo SBP (millimeters of mercury), DBP (millimeters of mercury), TC/HDL-c ratio, TC (millimoles per liter), LDL-c (millimoles per liter) 
Manios et al,36 1998 Greece IG: 288; CG: 183 6.5 First grade 45 min of practical physical education 2 d/wk with a shared PA component as a control; 4–6 h of theoretical physical education per y; 13–17 h of health and nutrition education; PA intensity: moderate The regular preschool schedule without health or physical education intervention 36 mo TC (milligrams per deciliter), LDL-c (milligrams per deciliter), HDL-c (milligrams per deciliter), triglycerides (milligrams per deciliter) 
Harrell et al,37 1996 United States IG: 588; CG: 686 9.5 Third and fourth grade Warm-up with 20 min of PA and cooldown 3 d/wk; classes on nutrition and smoking twice weekly; PA intensity: moderate No intervention 8 wk SBP (millimeters of mercury), DBP (millimeters of mercury), and TC (milligrams per deciliter) 
Vandongen et al,38 1995 Australia IG: 158; CG: 145 11 N/A 15 of min PA every school d with 6 30-min classroom PA lessons; PA intensity: moderate to vigorous No nutritional or physical fitness programs 9 mo SBP (millimeters of mercury), DBP (millimeters of mercury), and TC (millimoles per liter) 

N/A, not available.

The interventions consisted of PA during academic lessons or break-time activities.20,22,23,35 In 1 study, PA sessions were combined with short activity breaks,33 whereas the other programs included only PA sessions.21,24,32,34,36,38 The duration of these PA sessions ranged between 10 and 150 minutes. The program durations ranged from 8 weeks to 3 years, and the frequencies ranged between 2 sessions per day and 1 session monthly. The intensity of the PA sessions was not reported in 4 of the 19 studies29,31,34; the intensity was moderate in 5 of the remaining studies,21,22,32,36,37 vigorous in 4 studies,23,24,27,28 and moderate to vigorous in 6 studies.20,25,26,33,35,38 

The type of exercises developed in the PA programs included aerobic and mostly noncompetitive activities, such as running, jumping, rope skipping, dancing, climbing, and ball games, to improve aerobic capacity, coordination, flexibility, strength, and speed. One PA program23 was based on capoeira (a martial art in which fighting, dance, rhythm, and movement are combined). All PA sessions started with a warm-up and finished with a cooldown.

The outcomes were the most recognized cardiometabolic risk factors, including the following: (1) WC, which was reported in 11 studies21,24,26,31,33; (2) BP-related measures (SBP and DBP), which were reported in 11 studies* (although MAP was reported in only 2 studies,23,26 and therefore, a pooled ES was not calculated for MAP); (3) blood lipid–related outcomes, which included HDL-c in 6 studies,22,24,25,33,34,36 triglycerides in 7 studies,22,24,25,32,34,36 LDL-c also in 7 studies,22,24,26,34,36 and TC in 9 studies22,24,25,32,34,38; and (4) fasting glucose, which was reported in 4 studies,22,24,25,33 and fasting insulin, which was reported in 3 studies.22,25,26 

Data for adherence (understanding this one as attendance rate) was not reported in the majority of the studies. In the studies in which the authors reported adherence, it was >80% in 5 studies21,24,31,32,38 and ranged from 60% to 70% in 3 studies.20,26,28 Dropouts were reported in only 12 studies: drop-out values of <10% were presented in 2 studies,31,34 drop-out values between 10% and 20% were presented in 6 studies,22,24,30,33,35,36 and 4 drop-out values of >20% were presented in 4 studies.20,25,28,29 

The assessment of the risk of bias is displayed in Supplemental Fig 6. By domain, 63.2% and 68.4% of the included RCTs had shortcomings in the random sequence generation and allocation concealment, respectively; 21.1% of the included RCTs had an unclear risk of bias in the blinding of participants and personnel; in the outcome assessment domains, 89.5% and 84.2% of the included RCTs, respectively, obtained a low risk of bias in the incomplete outcome data and selective outcome reporting domains; and finally, 89.5% of the included RCTs obtained an unclear risk of bias in the other bias domain.

School-based PA interventions were associated with a significant decrease in WC (ES = −0.14; 95% CI: −0.22 to −0.07; P < .001; Fig 2), DBP (ES = −0.21; 95% CI: −0.42 to −0.01; P = .040; Fig 3), and fasting insulin (ES = −0.12; 95% CI: −0.20 to −0.04; P = .003; Fig 4).

FIGURE 2

Pooled ES (Cohen’s d) estimated for WC.

FIGURE 2

Pooled ES (Cohen’s d) estimated for WC.

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FIGURE 3

Pooled ES (Cohen’s d) estimated for BP-related outcomes.

FIGURE 3

Pooled ES (Cohen’s d) estimated for BP-related outcomes.

Close modal
FIGURE 4

Pooled ES (Cohen’s d) estimated for fasting glucose and insulin.

FIGURE 4

Pooled ES (Cohen’s d) estimated for fasting glucose and insulin.

Close modal

School-based PA interventions did not improve the fasting glucose (ES = −0.60; 95% CI: −1.28 to 0.08; P = .085; Fig 4), SBP (ES = −0.14; 95% CI: −0.31 to 0.03; P = .105; Fig 3), and lipid profiles for HDL-c (ES = 0.09; 95% CI: −0.05 to 0.23; P = .146), LDL-c (ES = −0.23; 95% CI: −0.52 to 0.07; P = .128), triglycerides (ES = 0.02; 95% CI: −0.11 to 0.15; P = .769), and TC (ES = −0.03; 95% CI: −0.37 to 0.31; P = .858; Fig 5).

FIGURE 5

Pooled ES (Cohen’s d) estimated for blood lipid–related outcomes.

FIGURE 5

Pooled ES (Cohen’s d) estimated for blood lipid–related outcomes.

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A meta-regression analysis was conducted to test the relationship between the pooled ES of each cardiometabolic risk factor and each of the following variables: the age at baseline, duration of PA sessions, frequency of PA sessions, and total duration of the program. The results of these meta-regression analyses are shown in Table 2.

TABLE 2

Meta-Regressions Coefficients

WCSBPDBPHDL-cLDL-cTriglyceridesTCGlucoseInsulin
Age .040a −.067a −.038a .086a .161a .042 .183a −.484a .047 
Duration of program .005a .004 .006 −.013a −.027a .008a −.015a .061a .004 
Frequency .023 .009 .005 .062 .298a .025 .348a .260a .045 
Duration of session .0001 .002 .002 .0008 .002 .0009 −.008a .023a .0008 
WCSBPDBPHDL-cLDL-cTriglyceridesTCGlucoseInsulin
Age .040a −.067a −.038a .086a .161a .042 .183a −.484a .047 
Duration of program .005a .004 .006 −.013a −.027a .008a −.015a .061a .004 
Frequency .023 .009 .005 .062 .298a .025 .348a .260a .045 
Duration of session .0001 .002 .002 .0008 .002 .0009 −.008a .023a .0008 

Values are β.

a

Statistical significance P < .05.

Subgroup analyses by the PA intensity category were performed only for the WC, SBP, and DBP variables because insufficient studies were available in each PA intensity category to conduct these analyses for the remainder of the variables.

No significant ES was observed when the relationship between the school-based PA interventions and BP was examined by the PA intensity category. In the case of WC, a significant effect was found in the moderate-to-vigorous (ES = −0.144 [95% CI: −0.25 to −0.04; P = .007]; I2 = 0% [P = .558]) and vigorous (ES = −0.129 [95% CI: −0.25 to −0.01; P = .032]; I2 = 35.3% [P = .201]) categories but not in the moderate PA intensity category.

High heterogeneity was observed for all variables except for fasting insulin (I2 = 0%; P = .602) and HDL-c (I2 = 48.2%; P = .085). Neither the Egger’s test nor the funnel plot revealed asymmetry, indicating an absence of publication bias (Supplemental Fig 7). In the sensitivity analysis, when each study was removed from the model, the results remained consistent across all exclusions except for glucose, which revealed significant reductions after removal of the study by Kriemler et al33; similarly, significant reductions in SBP were observed when the studies by Salcedo Aguilar et al32 and Adab et al20 were removed. For HDL-c, removing the studies by Manios et al36 and Hrafnkelsson et al25 revealed significant increases in the pooled ES. Regarding DBP, the removal of 6 studies resulted in significant decreases.21,24,25,33,35,37 

Our systematic review and meta-analysis suggest that school-based PA interventions are effective for improving WC, DBP, and fasting insulin in children. Although the magnitude of the effect seems to be small, it may be important for primary prevention strategies. All of these markers are components of metabolic syndrome (MetS), and authors of several longitudinal studies have reported that this cluster of cardiometabolic risk factors in infancy is a predictor of cardiovascular disease in adulthood.39,41 Moreover, according to Rose’s42 prevention theory, most cases of cardiometabolic diseases in adulthood will occur not in those at high risk but instead in those who have only some risk; thus, simply reducing the mean levels of the component variables of MetS is expected to greatly reduce the incidence of cardiovascular disease.

Although school-based PA interventions improved only 3 of the 9 cardiometabolic risk factors analyzed, the improvements in WC, DBP, and fasting insulin should not be underestimated. After translating these research findings into a measurable improvement in clinical outcomes,43 the school-based PA programs decreased the WC by 1.31 cm, the DBP by 1.68 mm Hg, and the fasting insulin level by 0.46 mU/L in the children.

The MetS definition includes WC as an adiposity marker instead of the BMI because abdominal obesity is considered a better predictor of cardiovascular disease risk factors in children than BMI.44 Our study revealed that school-based PA interventions achieved a decrease of 1.31 cm in the WC of the children. In adults, authors of a meta-analysis concluded that an increase of 1 cm in the WC was related to a 2% increase in the risk of future cardiovascular disease45; thus, a decrease in the WC of 1.31 cm in children is important for reducing the cardiometabolic risk profile. Furthermore, WC is an independent predictor of insulin resistance, plasma lipids, and BP.46,48 

On the basis of our results, our meta-analysis supports the finding that school-based PA programs slightly improve insulin levels (ES = −0.12; P = .003; 0.46 mU/L). However, in a smaller proportion, this finding is in accordance with a previous meta-analysis in which a moderate ES (−0.48) was reported that would equate to a decrease of 11.4 U/mL in fasting insulin.49 These findings revealed the usefulness of PA for reducing insulin levels; as a consequence, this decrease could also influence the prevention of MetS and type 2 diabetes in the future.49,50 Although school-based PA interventions revealed a trend toward better fasting glucose values, this association was not significant. This discrepancy may have occurred because the pancreatic β cells are still able to maintain normal glucose levels in the early stages of the insulin resistance process at the expense of overproduction of insulin; although not significant, the improvement in fasting glucose could also be due to an insufficient intensity of PA because a previous study revealed that fasting glucose was related to the total activity but not to light or moderate-to-vigorous PA.51 

A Cochrane review52 revealed that school-based PA interventions did not significantly improve SBP, although a positive and significant effect was found on DBP in children. Similarly, our pooled estimates revealed a significant reduction of 1.68 mm Hg in DBP but not in SBP. Although, the SBP pattern was similar to that of the DBP, the changes in SBP were not significant. This small ES on BP could have occurred because most of the subjects involved in these studies were children with normal BP levels, and thus, small reductions should be expected in this population. Differential effects on SBP and DBP have been repeatedly reported52,53 and may be a consequence of neurohumoral, vascular, and structural adaptations in response to PA.54 

Despite these results for SBP, authors of a previous meta-analysis in adults concluded that each 2-mm Hg decline in DBP could decrease the probability of suffering from a cardiovascular event by 12%.55 Considering this finding and the fact that BP levels in children are associated with a high risk of hypertension in adulthood,56 improvements in DBP in children are important for the prevention of cardiovascular diseases.

Regarding blood lipids, the authors of the same Cochrane review52 concluded that school-based PA interventions had a positive effect on the improvement of blood cholesterol in children, although our results did not confirm this finding. The current study revealed positive results for HDL-c, LDL-c, and TC, although these results did not reach statistical significance. A possible reason for this discrepancy is that the studies included in the Cochrane review also involved interventions promoting healthy eating, and it was unclear whether the improvement in blood cholesterol was a result of increased PA, changes in diet, or both. In our meta-analysis, only 3 of the 9 studies in which TC was reported included a nutritional education component.25,36,37 

Although HDL-c is most sensitive to PA, generally, changes in blood lipids depend on the PA time, volume, and intensity.57 Nevertheless, few differences were found between the durations of the interventions in which positive and negative blood lipid results were reported. This result was also found for the PA intensity. Of all of the included studies, only Muros et al24 showed an improvement in all blood lipid markers (HDL-c, LDL-c, triglycerides, and TC), and this PA program was the only one developed with vigorous intensity.

Our meta-analysis did not provide conclusive evidence about age, which had a significant relationship with all variables except triglycerides and insulin; nevertheless, the direction of this change is somewhat inconsistent. In this sense, the same inconclusive results were shown for the features of PA interventions; although we identified several characteristics of PA interventions in the meta-regression analyses that influenced cardiovascular risk factors, the direction of these relationships was not homogeneous, possibly because few studies included the reasons that linked their results with the characteristics of the intervention.

The subgroup analysis, which was based on the PA intensity, revealed maintenance of the effect on the decrease in WC with both moderate-to-vigorous and vigorous intensity but not with moderate intensity. Authors of a previous meta-analysis concluded that high moderate-to-vigorous PA was associated with better cardiometabolic risk factors in children and adolescents.58 

Evidence suggests that both PA and cardiorespiratory fitness (CRF) are independently related to the individual and the composite scores of cardiometabolic risk factors in children.6 In fact, authors of a recent study concluded that CRF was a marker of cardiovascular health in children and adolescents.59 Thus, children with poorer CRF have a higher risk of cardiovascular disease.60 We did not include CRF as a cardiovascular marker because the authors of a recent meta-analysis had concluded that school-based PA interventions improved CRF in children61; similar to our results, that study revealed that a high PA intensity was most effective at increasing the CRF and that the duration of the PA program and the duration and the frequency of the PA sessions did not influence the effect of the school-based PA programs.

Therefore, school-based PA interventions could play important roles in identifying and preventing cardiovascular disease risks in children, which could potentially influence the cardiovascular risk burden in adulthood as well as influence cardiovascular events.

Finally, in view of our results, the modest positive effects of school PA programs on children’s fasting insulin levels, WC, and BP have great importance for the health of schoolchildren because (1) the levels of these cardiometabolic parameters at early ages are predictors of cardiometabolic risk and events in adulthood; (2) general PA interventions at early ages are free of adverse consequences; (3) PA programs positively influence the whole cardiometabolic profile as opposed to approaches in which children are targeted on the basis of a single elevated factor (such as LDL-c or BP); and (4) although both population and high-risk strategies are important, according to Rose’s42 theory, population-based prevention strategies involving inexpensive and safe interventions can also be considerably more effective than high-risk approaches that include a limited number of individuals. Thus, although additional high-quality studies are necessary, the above considerations allow for us to recommend implementing PA that includes exercises at moderate-to-vigorous or vigorous intensity in the school setting.

This meta-analysis has some limitations that should be acknowledged. Some of these limitations, such as limited or incoherent information from studies, high heterogeneity, and risk of bias evaluations, are inherent to meta-analyses, and thus, conclusions should be interpreted after considering these limiting factors. Other weaknesses that are particularly important in our systematic review and meta-analysis are the following: (1) authors of few studies described in detail the implementation conditions of their interventions, and thus, the generalizability of these studies and the robustness of the results were limited; (2) the compliance rates were lacking in most studies, which were essential indicators of the feasibility of the interventions; (3) in most of the included RCTs, results were provided at the end of the intervention, but the long-term effects of the interventions and whether the improvements persisted over time were not included in our review; and (4) because of the scarcity of studies in which results by sex were provided, a subgroup analysis by sex was not possible. Lastly, estimating the pooled effect of school-based PA interventions on a cardiometabolic composite score would have been interesting because this analysis might have resulted in more accurate and comprehensive information about the real effects of school-based PA programs on cardiometabolic health; however, this analysis was not possible because a cardiovascular composite score was presented in only 1 study.33 

With our meta-analysis, we suggest that school-based PA interventions improve some cardiometabolic risk factors, such as WC, DBP, and fasting insulin, in children. High-intensity PA (moderate-to-vigorous or vigorous intensity) is the only strategy that has proven to be effective in reducing the WC. In general, other characteristics of PA interventions do not appear to have a significant influence on cardiometabolic risk factors.

BP

blood pressure

CG

control group

CI

confidence interval

CRF

cardiorespiratory fitness

DBP

diastolic blood pressure

ES

effect size

HDL-c

high-density lipoprotein cholesterol

IG

intervention group

LDL-c

low-density lipoprotein cholesterol

MAP

mean arterial pressure

MetS

metabolic syndrome

PA

physical activity

PRISMA

Preferred Reporting Items for Systematic Reviews and Meta-Analyses

RCT

randomized controlled trial

SBP

systolic blood pressure

TC

total cholesterol

WC

waist circumference

Dr Martínez-Vizcaíno was the principal investigator and guarantor, conceptualized and designed the study, was one of the main coordinators of the study, and reviewed and revised the manuscript; Ms Pozuelo-Carrascosa was one of the main coordinators of the study, designed the study, drafted the initial manuscript, and revised the manuscript; Dr Cavero-Redondo helped conduct the study, provided statistical and epidemiological support, helped write the manuscript, and revised the manuscript; Mr Herráiz-Adillo and Drs Sánchez-López and Díez-Fernández helped conduct the study and reviewed and revised the manuscript; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

This meta-analysis has been registered with the PROSPERO International prospective register of systematic reviews (https://www.crd.york.ac.uk/prospero/) (identifier CRD42018082416).

*

Refs 20, 21, 24, 25, 28, 3235, 37, and 38.

FUNDING: Ms Pozuelo-Carrascosa is supported by a grant from the Spanish Ministry of Education, Culture, and Sport (FPU14/01370). Dr Cavero-Redondo is supported by a grant from the Universidad de Castilla-La Mancha (FPU13/01582).

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Competing Interests

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

Supplementary data