Cardiorespiratory fitness and cardiovascular disease risk factors in children and adolescents

Cardiovascular disease (CVD) events occur most frequently during or after the fifth decade of life, however, there is evidence indicating that the precursors of CVD has its origin already in the first or second decade of life. Low levels of physical activity and cardiorespiratory fitness are major modifiable determinants for the development of CVD in adults. The overall aim of the present thesis was to study the associations between physical activity, cardiorespiratory fitness, fatness and CVD risk factors in children and adolescents from the Estonian and Swedish part of the European Youth Heart Study. Physical activity was measured by accelerometry, and cardiorespiratory fitness was estimated by a maximal ergometer bike test. Total and central body fat were derived from the sum of five skinfold thicknesses and waist circumference, respectively. Additional measured outcomes included fasting insulin, glucose, triglycerides, high density lipoprotein cholesterol, total plasma homocysteine (tHcy), and blood pressure. Genotyping for the methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism was done by DNA sequencing. The main outcome was that cardiorespiratory fitness was negatively associated with clustering of CVD risk factors in children. Moreover, the results suggested that there is a cardiorespiratory fitness level for having a low metabolic risk. The results also indicated that the deleterious consequences ascribed to high levels of total and central fatness could be counteracted by having high levels of cardiorespiratory fitness. On the other hand, the levels of tHcy in children and adolescents were not influenced by the levels of physical activity, cardiorespiratory fitness, and body fat even after controlling for presence of the MTHFR 677C>T genotype, the main influence on tHcy levels in these individuals. To improve fitness and reduce fatness in children, moderate and vigorous intensity physical activity may have a greater impact than lower physical activity intensity levels. The data call for the development and testing of preventive strategies, especially for those children with low cardiorespiratory fitness. Longitudinal and interventional studies are needed in order to clarify if changes in physical activity and cardiorespiratory fitness may favourably influence the levels of CVD risk factors already in these ages, and in a long perspective of time