Doctoral Dissertations

Date of Award

5-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Exercise Science

Major Professor

Eugene C. Fitzhugh

Committee Members

Edward T. Howley, Dixie L. Thompson, David R. Bassett, Lisa Jahns

Abstract

The purpose of this study was to evaluate the current prevalence of the metabolic syndrome with an emphasis on examining the relationship between leisure time physical activity (LTPA) and the metabolic syndrome in a nationally representative sample of the United States (U.S.) adult population within the 1999-2004 National Health and Nutrition Examination Survey (NHANES). The sample for this study included adults (N=5620), 20 years and older, who attended a mobile examination center (MEC) examination in the NHANES 1999-2004. The American Heart Association and National Heart, Lung, and Blood Institute (AHA/NHLBI) AHA/NHLBI definition was used to define the metabolic syndrome based on the results of a preliminary pilot study found in Appendix A. A metabolic syndrome risk score (MSRS), ranging from 0 to 5 was created to sum cardiovascular (CV) risk factors. Accumulating a MSRS ≥ 3 designated a metabolic syndrome diagnosis, a dependent variable within this study. Physical activity (PA) was measured in two ways; a six-level measure of MET·minutes per week, comprised of PA frequency, intensity, and duration and a three-level variable (no leisure-time physical activity (LTPA), insufficient LTPA, and an LTPA level equivalent to meeting the CDC/ACSM PA recommendation) associated with the current Centers for Disease Control and American College of Sports Medicine public health PA recommendation (CDC/ACSM). SUDAAN statistical software was used to estimate age-adjusted prevalence and logistic and multi-logistic odds risk ratios.

The overall age-adjusted prevalence of the metabolic syndrome among the U.S. adult population was 36.3%. A significant difference was found for metabolic syndrome prevalence between those meeting the current public health PA recommendation (29.0%) and those reporting no LTPA (40.0%). Adults who acquired between 736.55 and 1360.15 MET·min·wk-1 of LTPA were found to be 35% (OR 0.65; 95% Cl 0.48-0.88) less likely to meet the AHA/NHLBI metabolic syndrome diagnosis criteria compared to those reporting no LTPA. A similar inverse association was found for an increasing the MSRS (OR 0.69; 95% Cl 0.56-0.85). The strength of this inverse association increased (OR 0.55; 95% Cl 0.42-0.71) when weekly LTPA MET·minutes reached >1360.15 MET·min·wk-1. This inverse association was also found for an MSRS (OR 0.58; 95% Cl 0.48- 0.70) at this level of LTPA.

These findings estimate one in three U. S. adults have the metabolic syndrome. This study consistently showed an inverse association between LTPA and metabolic syndrome risk. Furthermore, there appeared to be a stronger inverse association between metabolic syndrome and LTPA when LTPA volume was increased. However, this additional decrease in risk associated with increasing volumes of LTPA may likely revolve around improvements in body composition. Improvements in body composition associated with varying frequencies, intensities, and duration of PA may improve other components defining the metabolic syndrome (i.e. hypertension, obesity.) While this study is cross-sectional and causality cannot be inferred due to the nature of self-reported data, our findings do illustrate a strong inverse association for LTPA and the metabolic syndrome. Researchers can feel confident that if LTPA is measured using all three components (frequency, intensity, and duration) necessary to calculate MET·min·wk-1, that relationships with the metabolic syndrome and its individual defining criteria will be detected. These results support the need for future longitudinal studies and randomized control trials examining PA volume and metabolic syndrome risk.

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