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Cardiorespiratory Fitness Is Strongly Related to the Metabolic Syndrome in Adolescents

¹ School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada
² Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada

Address correspondence and reprint requests to Ian Janssen, PhD, School of Kinesiology and Health Studies, Queen's University, 69 Union St., Kingston, Ontario, Canada, K7L 3N6. E-mail: ian.janssen{at}queensu.ca

Abbreviations: CRF, cardiorespiratory fitness • NCEP, National Cholesterol Education Program • NHANES, National Health and Nutrition Examination Survey

	INTRODUCTION

TOP INTRODUCTION RESEARCH DESIGN AND METHODS-- RESULTS-- CONCLUSIONS-- References

 
The metabolic syndrome is a predecessor of type 2 diabetes and cardiovascular disease (1). In adults, physical activity is important for both preventing and treating metabolic syndrome (2). A limited number of studies have examined the impact of physical activity on metabolic syndrome in youth (3–7). The results from the few existing studies are conflicting, reporting no associations, weak effects, and strong effects of physical activity (3–7). These inconsistencies may reflect that most of these studies measured physical activity using self-report questionnaire measures, which have limited validity and reliability in youth (8,9). While one paper reported that the beneficial effects of physical activity on metabolic syndrome are limited to girls (3), published studies of physical activity and metabolic syndrome in youth have been limited to predominantly Caucasian samples and lack ethnic comparisons. Thus, it is unknown whether the effects of physical activity on metabolic syndrome are consistent in different population groups. The purpose of this study is to 1) examine the relation between objective measures of cardiorespiratory fitness (CRF) (the ability to perform endurance activities) and metabolic syndrome in adolescents and 2) determine whether the relationship is consistent by sex and ethnicity.

	RESEARCH DESIGN AND METHODS—

TOP INTRODUCTION RESEARCH DESIGN AND METHODS-- RESULTS-- CONCLUSIONS-- References

 
The study sample consisted of 1,561 adolescents, aged 12–19 years, who participated in the National Health and Nutrition Examination Survey (NHANES) 1999–2002, which is a nationally representative cross-sectional survey (10). All participants had a complete fasting (12 h) blood sample and measures of waist circumference, blood pressure, and CRF.

Maximal aerobic capacity (VO_2max) was the objective CRF measure obtained in NHANES. VO_2max is a health-related component of physical fitness that relates to the ability of the circulatory and respiratory systems to supply oxygen during sustained physical activity (11). VO_2max was estimated from heart rate measurements obtained during a multistage submaximal test where participants walked or ran on a treadmill to achieve 75–90% of their age-predicted maximal heart rate (12). Estimated VO_2max was regressed on age within each sex, and the residuals were retained to represent age-adjusted values. The sample was then divided into low, moderate, and high CRF tertiles based on the age-adjusted VO_2max values.

In adults, the metabolic syndrome criteria established by the National Cholesterol Education Program (NCEP) is consistently used in research and clinical settings (13). According to the NCEP, metabolic syndrome includes having three or more of the following: high waist circumference (102 cm in men and 88 cm in women), high plasma triglycerides (>1.69 mmol/l), low HDL cholesterol (<1.04 mmol/l in men and <1.29 mmol/l in women), high fasting plasma glucose (5.6 mmol/l), and high blood pressure (130/85 mmHg). There is no universally accepted metabolic syndrome criterion for adolescents. In this study, we used age- and sex-specific metabolic syndrome thresholds for adolescents that were linked to the NCEP adult thresholds using growth curve modeling (14). The growth curves for each metabolic syndrome component pass through the adult thresholds at 20 years such that adolescent thresholds are linked to the adult thresholds noted above. Thus, metabolic syndrome for adolescents was defined as having three or more of the five metabolic syndrome components using the adolescent thresholds.

Statistical analyses were performed using Stata Intercooled 7 (StataCorp) to account for the complex design and weighting of NHANES. The prevalence of metabolic syndrome was compared across CRF tertiles using ² analyses. The odds of having metabolic syndrome and its component risk factors were compared across CRF tertiles using logistic regression analyses. Age, ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other races including multiracial), poverty-to-income ratio (based on family income and size, divided into quartiles), smoking (never, former, or current), carbohydrate consumption (percentage of calories from carbohydrate, with <40% as low, 40–60% as moderate, and >60% as high), and fat consumption (percentage of calories from fat, with <30% as low, 30–40% as moderate, and >40% as high) were included as confounders in the logistic regression analyses.

	RESULTS—

TOP INTRODUCTION RESEARCH DESIGN AND METHODS-- RESULTS-- CONCLUSIONS-- References

 
The prevalence of metabolic syndrome was 7.6% in the entire sample. The prevalence of metabolic syndrome decreased across low, moderate, and high CRF tertiles within both male (24.3, 5.0, and 0.1%, respectively) and female (17.3, 5.9, and 0.9%) subjects and also within the non-Hispanic white (30.0, 6.0, and 0.5%, respectively), non-Hispanic black (21.3, 5.0, and 0.5%), and Hispanic (14.4, 6.5, and 0.9%) ethnic groups.

In comparison with the low CRF tertile (referent group, odds ratio [OR] 1.00), the likelihood of having any of the individual metabolic syndrome components was significantly lower in the high CRF tertile (P < 0.05). The ORs (95% CIs) for metabolic syndrome components in the high CRF tertile were as follows: 0.02 (0.01–0.05) for high waist circumference, 0.18 (0.11–0.28) for low HDL cholesterol, 0.24 (0.13–0.42) for high triglycerides, 0.51 (0.27–0.96) for high plasma glucose, and 0.17 (0.09–0.32) for high blood pressure. As shown in Table 1, the ORs for metabolic syndrome decreased in a gradient manner when moving from low to moderate to high CRF tertiles. These results were consistent within all sex and ethnic groups (Table 1). Given the small number of subjects (n = 72), analyses were not performed within the "other" race group.

	CONCLUSIONS—

TOP INTRODUCTION RESEARCH DESIGN AND METHODS-- RESULTS-- CONCLUSIONS-- References

The strengths of this study include the large and representative study sample (10), the use of age-appropriate adolescent metabolic syndrome criteria that are linked to health-based adult criteria (14), and the use of an objective CRF measure, which is largely determined by physical activity participation in recent weeks and months (11). The use of strong measures may help explain the strength of the relations observed in this study. Most previous studies in this topic have relied on questionnaire measures of physical activity, the imprecision of which may have biased the results toward a null effect.

The findings presented in this report provide compelling evidence that moderate and high CRF levels are associated with a significantly lower metabolic syndrome prevalence in adolescents. Therefore, interventions aimed at combating metabolic syndrome in this age-group may want to focus on improving CRF.

	Footnotes

 
Published ahead of print at http://care.diabetesjournals.org on 29 May 2007. DOI: 10.2337/dc07-0734.

A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C Section 1734 solely to indicate this fact.

Received for publication April 16, 2007. Accepted for publication May 18, 2007.

	References

TOP INTRODUCTION RESEARCH DESIGN AND METHODS-- RESULTS-- CONCLUSIONS-- References

 

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6. Ruiz JR, Ortega FB, Rizzo NS, Villa I, Hurtig-Wennlof A, Oja L, Sjostrom M: High cardiovascular fitness is associated with low metabolic risk score in children: the European Youth Heart Study. Pediatr Res 61:350–355, 2007[Medline]
   
7. Kelishadi R, Razaghi EM, Gouya MM, Razaghi EM, Delavari A, Majdzadeh R, Heshmat R, Motaghian M, Barekati H, Mahmoud-Arabi MS, Riazi MM; CASPIAN Study Group: Association of physical activity and the metabolic syndrome in children and adolescents: CASPIAN Study. Horm Res 67:46–52, 2007[Medline]
   
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11. U.S. Department of Health and Human Services: Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Department of Health and Human Services, 1996
    
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14. Jolliffe CJ, Janssen I: Development of age-specific adolescent metabolic syndrome criteria that are linked to the Adult Treatment Panel III and International Diabetes Federation criteria. J Am Coll Cardiol 49:891–898, 2007[Abstract/Free Full Text]
    
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This Article Extract Full Text (PDF) All Versions of this Article: dc07-0734v1 30/8/2143    most recent Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Janssen, I. Articles by Cramp, W. C. Search for Related Content PubMed PubMed Citation Articles by Janssen, I. Articles by Cramp, W. C. Social Bookmarking                What's this?