Associations between physical activity and metabolic risk factors in children and adolescents : The European Youth Heart Study (EYHS)

Sammanfattning: Background: Sedentary lifestyles and concomitant behaviours such as smoking and poor dietary habits are increasingly implied in the rise of non communicable diseases which have become a major cause of morbidity and death not only in high income countries but also in lower income countries. This development makes it increasingly important to study aetiological factors that are linked to features of the metabolic syndrome in children and adolescents. Special consideration should be given to behavioural and lifestyle factors that are more readily adaptable and may have an early advantageous effect on metabolic risk factors. Objectives: To examine the relationship between physical activity, cardiorespiratory fitness and metabolic risk factors in healthy children and adolescents. Research Design: The data used in the analysis was collected as part of the Estonian and Swedish section of the European Youth Heart Study (EYHS). The EYHS is a school based, multi center, cross sectional study designed to examine the nature and the interactions between individual, lifestyle and environmental factors in their relationship to cardiovascular risk. The main variables under investigation were total physical activity and activity intensity levels measured by accelerometry; cardiorespiratory fitness measured by maximal ergometer bike tests; markers of body fat; fasting serum levels of insulin, glucose, triglycerides, total and HDL cholesterol; pubertal and socioeconomic status. Results: A) Total, moderate vigorous and vigorous physical activity were positively associated with cardiorespiratory fitness. B) Lower body fat levels were associated with greater time periods spent at vigorous levels of physical activity. C) Body fat was positively correlated with metabolic risk factors and may act as a mediator in the association between cardiorespiratory fitness with metabolic risk. D) Cardiorespiratory fitness was more strongly correlated to clustered metabolic risk factors than total physical activity and may have mediated the effect of physical activity on metabolic risk. E) The associations between physical activity and insulin resistance were strongest at higher levels of physical activity. F) Children of the lowest socioeconomic status spent more time in sedentary behaviours such as watching TV but were not less physically active than their peers. G) Time periods spent in total physical activity are greater on school days than on weekends and a social gradient is observed in girls. Conclusion: The results presented in this thesis reemphasize the importance of physical activity as an integral part of a health enhancing lifestyle. They show that associations and interactions between physical activity and markers of metabolic risk can be observed at an early age and can provide important insights into the aetiology of metabolic disease patterns.