CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Ian Janssen, PhD* and
Courtney J. Jolliffe, MSc
* School of Kinesiology and Health Studies, Queen’s University, Kingston, Ontario, Canada K7L 3N6 (Email: ian.janssen{at}queensu.ca).
We appreciate the letter by Drs. Lobelo and Ruiz that was written in response to our recent article in which we developed age-specific metabolic syndrome (MetS) criteria for adolescents age 12 to 20 years (1). As correctly pointed out in their letter, and as indicated in our article (2), the prevalence of some of the MetS components have changed in the period between the third (1988 to 1994) and continuous (1999 to 2002) National Health and Nutrition Examination Surveys (NHANES). Although we combined these data sets in our article, this was not problematic given that the adolescent MetS component cut-points that we developed were not tied to a given percentile (i.e., the 95th percentile). Rather, the adolescent MetS component cut-points were tied to the percentile that corresponds to the adult health-based cut-point at 20 years of age. Although this percentile may be different in the older and new NHANES surveys, because the curves are linked to the adult cut-points, the resultant adolescent cut-points would likely end up being the same no matter what database or combination of databases was used.
As physical activity scientists who work within a school of kinesiology and health studies, it is only intuitive that we fully support and agree with the position of Drs. Lobelo and Ruiz that cardiorespiratory fitness (CRF) is a strong and independent determinant of MetS and cardiovascular risk in people of all ages. In fact, our laboratory will be presenting work this June at the International Conference on Physical Activity and Obesity in Children that indicates that the prevalence of MetS in adolescent NHANES 1999 to 2002 participants decreased from 24.3% to 5.0% to 0.1% across low, moderate, and high CRF tertiles. However, we do not agree with the position of Lobelo and Ruiz that CRF should be used as one of the criteria to explore the accuracy of MetS as a risk stratification tool. Within the causal chain, CRF precedes the MetS (CRF is the exposure and MetS is the outcome). When validating criteria for defining a risk factor, such as MetS, it should be based on whether or not that risk factor (or exposure) predicts the outcome(s) it is a risk factor for, and not how it relates to other variables that are downstream in the causal chain. Thus, we believe that the validation of the MetS criteria developed in our study should be based on the ability of MetS to predict cardiometabolic outcomes, which in youth may consist of intermediate outcomes such as atherosclerotic lesions and endothelial dysfunction.
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References
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- 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 2007;49:891-898.[Abstract/Free Full Text]
- Ogden CL, Flegal KM, Carroll, MD, Johnson CL. Prevalence and trends in overweight among US children and adolescents, 1999–2000 JAMA 2002;288:1728-1732.[Abstract/Free Full Text]
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