The high prevalence of overweight and obesity among children and adolescents and low proportion of youth meeting national physical activity guidelines are major public health concerns. The influence of fatness on the development of atherosclerosis and cardiovascular disease (CVD) risk factors, including elevated blood pressure and elevated C-reactive protein (CRP), have been well documented. The influence of physical activity on these same CVD risk factors is less understood, though physical activity is considered a cornerstone in the prevention and treatment of obesity and CVD risk factors. Although the independent relationships between physical activity and fatness on CVD risk factors have been examined, the combined association of fatness and physical activity with these risk factors is not well understood in children and adolescents. Therefore, the purpose of this dissertation was to examine the combined association (interaction) of fatness and physical activity with blood pressure and CRP in two large nationally represented samples of children and adolescents, one from the United States (National Health and Nutrition Examination Survey) and the other from the United Kingdom (East of England Healthy Hearts Study). The analysis from the United States included both blood pressure and CRP, while the analysis from the United Kingdom focused only on blood pressure. In each sample, subjects were classified by fatness (normal weight, overweight, obese) via body mass index and physical activity level (least active, low active, active) via questionnaire or accelerometry. Analyses were conducted for the total sample and for age and sex categories when appropriate. Main effects and the combined association (interaction) of fatness and physical activity were examined by analysis of covariance and multiple linear regression. Logistic regression was performed to determine the influence of age, sex, fatness, and physical activity on having high-normal blood pressure or high blood pressure. Overall, fatness was consistently shown to have a positive relationship with blood pressure and CRP in both samples. Physical activity was inversely related with blood pressure and CRP consistently in girls, but not in boys. No combined association between fatness and physical activity with blood pressure was evident in the United Kingdom sample. However, there was a combined association between fatness and physical activity with blood pressure in the United States sample. Again, this relationship was seen consistently in girls, but not evident in boys. There was also a combined association between fatness and physical activity with CRP in the United States sample. This interaction was seen in both boys and girls. The results of this study indicate that fatness has a strong influence on blood pressure and CRP. The combined association between fatness and physical activity with blood pressure and CRP is novel and highlights the importance of both factors when working to improve the overall cardiovascular health of children and adolescents. This relationship has been observed with aerobic fitness but the results of this study highlight that physical activity, both moderate and vigorous intensity, is beneficial.
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