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Diabetes Care 31:e9 2008
DOI: 10.2337/dc07-2165
© 2008 by the American Diabetes Association
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Online Letters: Comments and Responses

Cardiorespiratory Fitness Is Strongly Related to the Metabolic Syndrome in Adolescents

Response to Shaibi, Cruz, and Goran

Ian Janssen, PHD1,2 and Wendy Cramp, BSC1

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

Address correspondence 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

We respectfully disagree with both issues raised by Shaibi, Cruz, and Goran (1). First, we will address the comment that "associations between fitness and activity are weak at best." The review article referenced by Shaibi, Cruz, and Goran was based on observational studies published before 1995, a time at which physical activity was measured almost exclusively by questionnaire. Since 1995, several studies have shown that questionnaire measures of physical activity in youngsters only modestly correlate with direct measures obtained by accelerometry (2,3) and, more importantly, that accelerometry-based measures of physical activity relate to cardiorespiratory fitness (CRF) in the pediatric population (4,5). Furthermore, intervention studies have reported significant improvements in CRF in response to physical activity programs in children and youth (6,7). Thus, while we agree that CRF is in part accounted for by genetics, current evidence also substantiates our claim that CRF is largely influenced by physical activity.

We would also like to comment on the contention that CRF would not have been an independent predictor of the metabolic syndrome had we controlled for adiposity. Recall that one of the five components of the metabolic syndrome as defined in our study was abdominal obesity (e.g., high waist circumference) (8). Because adiposity itself was a component of the outcome measure, from a statistical standpoint it would have been inappropriate to control for part of the outcome measure (adiposity) when examining the relation between the exposure (CRF) and outcome (metabolic syndrome). Thus, while we agree that adiposity, particularly abdominal fat, is a central feature of the metabolic syndrome, we disagree with the flawed rationale of Shaibi, Cruz, and Goran that CRF should not be considered an independent predictor of metabolic syndrome. In fact, we suggest that the effect of physical activity and CRF on adiposity is one of the primary pathways by which these exposures influence the metabolic syndrome.

References

  1. Shaibi GQ, Cruz MC, Goran MI: Cardiorespiratory fitness is strongly related to the metabolic syndrome in adolescents (Letter). Diabetes Care 31: e8, 2008. DOI: 10.2337/dc07-2133[Free Full Text]
  2. Wong SL, Leatherdale ST, Manske SR: Reliability and validity of a school-based physical activity questionnaire. Med Sci Sports Exerc 38: 1593–1600, 2006
  3. Bender JM, Brownson RC, Elliott MB, Haire-Joshu DL: Children's physical activity: using accelerometers to validate a parent proxy record. Med Sci Sports Exerc 37: 1409–1413, 2005
  4. Plasqui G, Westerterp KR: Accelerometry and heart rate as a measure of physical fitness: cross-validation. Med Sci Sports Exerc 38: 1510–1514, 2006
  5. Dencker M, Thorsson O, Karlsson MK, Linden C, Svensson J, Wollmer P, Andersen LB: Daily physical activity and its relation to aerobic fitness in children aged 8–11 years. Eur J Appl Physiol 96: 587–592, 2006[Medline]
  6. Schneider M, Dunton GF, Bassin S, Graham DJ, Eliakim AF, Cooper DM: Impact of a school-based physical activity intervention on fitness and bone in adolescent females. J Phys Act Health 4: 17–29, 2007[Medline]
  7. Carrel AL, Clark RR, Peterson SE, Nemeth BA, Sullivan J, Allen DB: Improvement of fitness, body composition, and insulin sensitivity in overweight children in a school-based exercise program: a randomized, controlled study. Arch Pediatr Adolesc Med 159: 963–968, 2005[Abstract/Free Full Text]
  8. Janssen I, Fortier A, Hudson R, Ross R: Effects of an energy-restrictive diet with or without exercise on abdominal fat, intermuscular fat, and metabolic risk factors in obese women. Diabetes Care 25: 431–438, 2002[Abstract/Free Full Text]

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This Article
Right arrow Extract Freely available
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Right arrow Articles by Janssen, I.
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