Physical activity, sedentary behaviour, physical fitness and inflammatory biomarkers in children and adolescentes. Actividad física, hábitos sedentarios, condición física, y biomarcadores inflamatorios en niños y adolescentes

Abstract

Cardiovascular diseases (CVD) are the main cause of mortality in the world(1). Episodes of CVD are found mainly during or after the fifth decade of life. However there are evidences indicating that precursors of CVD have their origins during childhood and adolescence(2,3). In fact, it has been shown that levels of CVD during childhood are predictors of CVD risk during adulthood(4-7). Between the main conventional CVD risk factors we found, obesity, hypertension, insulin resistance and dyslipidemia(8). A better understanding of the mechanism that affect risk factors for CVD during childhood and adolescence would contribute to the development of effective prevention programs, a better counseling and a shift towards correct public health policies. In the last decades, numerous studies have found the existence of new CVD risk factors, among which are the inflammatory biomarkers(9). The overall objective of the present doctoral thesis was to study the influence of the physical activity, sedentary behaviour and physical fitness levels as well as the neck circumference on emerging CVD risk factors in children and adolescents. To address these aims 3 studies were conducted from data gathered in the UP&DOWN study. Study I was conducted in a population of 481 participants (229 children; 252 adolescents) from the UP&DOWN study. Study II was performed with 503 participants (230 children; 273 adolescents) from the UP&DOWN study. In the study III 2198 participants were included, (1179 children; 1019 adolescents) belonging to the UP&DOWN study. The main findings of this Doctoral Thesis were: i) Physical activity and sedentary behaviour levels were inversely and positively associated, respectively, with levels of inflammatory biomarkers in children and adolescents; however, when physical fitness levels were taken into account, almost all associations disappeared. ii) Physical fitness, mainly cardiorespiratory fitness and upper body muscular fitness, were inversely associated with inflammatory biomarkers in children and adolescents independently of body mass index. iii) Neck circumference was positively associated with other anthropometric and body composition indexes, as well as with independent cardiovascular risk factors grouped in children and adolescents. The results of this doctoral thesis have helped broaden the knowledge about the relationship between physical activity levels, sedentary behaviour, physical fitness and neck circumference with emerging cardiovascular risk factors in children and adolescents. The results suggest that a regular practice of physical activity in order to improve physical fitness levels, as well as a shorter time invested in sedentary behaviour, could contribute to an improvement in the inflammatory profile and reduce the risk of CVD in children and adolescents. In addition, cut-off values to classify children and adolescents as normal weight and overweight/obese have been identified, based on prediction equations using body mass index, waist circumference and body fat percentage.