| 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 these research does not provide a clear picture of the true relation between physical activity and health. In addition, setting appropriate benchmarks or cut-off points for health-related steps are necessary to guide physical activity surveillance, intervention, and evaluation. However, there is currently no consensus on steps cut-off points for children and adolescents.ObjectivesResearch 1. Describe the dose-response relation between moderate-to-vigorous physical activity (MVPA) and cardiometabolic health in children and youth.Research 2. Establish preliminary criterion-referenced standards for physical activity using steps/day related to cardiometabolic health in children and adolescents, and evaluate previously available steps/day cut-off points.Taken together, the overall objective of this dissertation was to examine the dose-response relation between objectively measured physical activity and cardiometabolic health in youth and determine how this may affect current American physical activity and walking.MethodsBoth research 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 overweight/obesity, hypertension, hyperlipidemia, and metabolic syndrome. Receiver operating characteristic (ROC) was used to identify and evaluate steps/day cut-off values in reference to childhood weight status, blood pressure status, lipid profile status, and metabolic risk status. ResultsResearch 1.①The likelihood of having overweight/obesity decreased in a curvilinear manner with increasing minutes of MVPA. At 15,30,45 and 60 min/d of MVPA the risk ratios for overweight/obesity were 0.46,0.2,0.13, and 0.1, respectively, in comparison to 1 minute of MVPA;②The likelihood of having hypertension decreased in a curvilinear manner with increasing minutes of MVPA. At 15,30,45 and 60 min/d of MVPA the risk ratios for hypertension were 0.65,0.49, 0.42, and 0.37, respectively, in comparison to 1 minute of MVPA;③Risks for high-risk high density lipoprotein cholesterol (HDL-C) and triglyceride (TG) values decreased in a curvilinear manner with increasing minutes of MVPA. At 15,30,45 and 60 min/d of MVPA the risk ratios for high-risk HDL-C were 0.3,0.25,0.24, and 0.22, respectively, in comparison to 1 minute of MVPA. And, at 15,30,45 and 60 min/d of MVPA the risk ratios for high-risk TG were 0.42,0.23,0.17, and 0.11, respectively, in comparison to 1 minute of MVPA. The relation between level of MVPA and LDL-cholesterol was unclear.④The likelihood of having metabolic syndromes decreased in a curvilinear manner with increasing minutes of MVPA. At 15,30,45 and 60 min/d of MVPA the risk ratios for hypertension were 0.68,0.45, 0.34, and 0.23, respectively, in comparison to 1 minute of MVPA.Research 2.①The mean (SD) steps/day for boys, girls, and sexes combined in U.S were 12780 (3348),11202 (2908), and 11981 (3410), respectively.②Depending on the currently steps/day cut-off points, approximately 28-68% of children and youth did not meet the recommended number of steps/day.③Based on weight status, the selected cut points for steps/day for children were 12500 steps/day for girls and 13000 steps/day for boys, for adolescents were 12000 steps/day for girls and 10500 steps/day for boys. And based on blood pressure status, the selected cut points for steps/day for children were 12000 steps/day for girls and 12500 steps/day for boys, for adolescents were 10000 steps/day for girls and 12000 steps/day for boys. Based on HDL-C status, the selected cut points for steps/day for children were 8500 steps/day for girls and 10000 steps/day for boys. Based on TG status, the selected cut points for steps/day for adolescents were 9500 steps/day for girls and 10500 steps/day for boys. Based on metabolic syndrome risk factor status, the selected cut points for steps/day for adolescents were 11000 steps/day for girls and 10000 steps/day for boys.④Sensitivity was high and specificity was low for current steps/day cut-off points evaluated. The ROC analysis indicated that lowering the steps/day cut-ff points for boys and girls may increase accuracy.ConclusionsResearch 1. A modest dose-response relation was observed between MVPA and overweight/obesity, hypertension, hyperlipidemia, and metabolic syndromes. These results support the public health recommendation that children and youth accumulate at least 60 minutes of MVPA daily. However, because children and adolescents can achieve significant cardiovascular health benefits with even modest amounts of MVPA, physical activity guidelines for youth may need to recognize that getting youngsters to engage in less than the currently recommend≥60 min/day of MVPA is beneficial. This is an important message given that 65 percent of children and youth in this study did not even accumulate 30 min of MVPA on the average day. A minimal MVPA target of 30 min/day may act as a stepping stone for currently sedentary children, who upon reaching this stepping stone, could be encouraged to strive for the recommend≥60 min/day.Research 2. This study demonstrates that a large percentage of children and youth from U.S national representative sample do not meet current steps/day based physical activity recommendations. Children should walk 13000 steps/day for boy and 12500 steps/day for girls, adolescents should walk 12000 steps/day for boy and 10500 steps/day for girls, if they want to achieve good cardiometaboic health and decrease the health risk. Currently steps/day cut-off points is not suitable for children and youth in U.S., TL and DK cut-off point is too high for American children and adolescents.
|
PDF Full Text Request