Recommendations for Minimal and Optimal Amounts of Physical Activity to Reduce the Risk of Dyslipidemia in Youth
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Background: Physical inactivity has been consistently associated with numerous negative health outcomes that track from childhood into adulthood, making physical activity a special concern in the pediatric population. Dose-response studies are particularly useful when trying to understand the minimal and optimal amounts of physical activity needed to reduce the risk of negative health outcomes. Unfortunately, previous work within youth has relied on self-reported measures of physical activity, and this research does not provide a clear picture of the true relation between physical activity and health. Objectives: Manuscript 1. Describe the dose-response relation between dyslipidemia and moderate-to-vigorous physical activity (MVPA) in youth. Manuscript 2. Quantify the difference between self-reported and objectively measured MVPA in youth. Taken together, the overall objective of this thesis was to examine the dose-response relation between objectively measured MVPA and dyslipidemia in youth and determine how this may affect current Canadian physical activity guidelines. Methods: Both manuscripts used data from the U.S. National Health and Nutrition Examination Survey. Fractional polynomial regression modeling was used to fit the dose-response curves between MVPA and lipid/lipoprotein measurements. Regression analysis as well as a Bland-Altman plot was used to explain the discrepancy between self-reported and objective measures of MVPA. All analyses were completed using SAS statistical software. Results: Manuscript 1. Risks for high-risk HDL-cholesterol and triglyceride values decreased in a curvilinear manner with increasing minutes of MVPA. The greatest reduction in risk occurred within the first 30 min/d of MVPA. The relation between level of MVPA and LDL-cholesterol was unclear. Manuscript 2. The average youth over-reported their MVPA by ~30 min/d. The over-reporting was not mediated by basic demographic factors; however, the difference in reporting was systematic in nature such that inactive youth over-reported to the greatest extent. Conclusions: Manuscript 1. Youth need to accumulate 30 min/d of MVPA to greatly reduce their risk for dyslipidemia. Manuscript 2. Youth tend to over-report their daily MVPA by approximately 30 min/d. Combined, the results from this thesis suggest that physical activity recommendations for cardiovascular health in youth should suggest a minimum of 30 min/d of MVPA and preferred level of 60 min/d.