Fitness, fatness, and coronary heart disease risk in adolescents: the Northern Ireland Young Hearts Project

Purpose: The purpose of this study was to examine the independence and rela tive strengths of association between coronary heart disease (CHD) risk sta tus and both body fatness and cardiorespiratory (C-R) fitness in 12- and 15 -yr-old adolescents, Methods: The study cohort consisted of 1015 schoolchil dren aged 12 and 15 yr (251 12-yr-old boys, 258 17-yr-old girls, 252 15-yr- old boys, and 251 15-yr-old girls), representing a 2% random sample of each population group. For each child, height, weight, sexual maturity (puberta l status), skin-fold thicknesses (4 sites), blood pressure (random zero sph ygmomanometer), nonfasting serum total, and high density lipoprotein (HDL)- cholesterol and C-R fitness (20-m shuttle run; 20-MST) were determined unde r standardized conditions. Socioeconomic status and habitual physical activ ity were also determined from questionnaire information. Multiple regressio n analyses were carried out to examine relationships between five CHD risk factors, and fitness and fatness and to examine the relative strengths of f itness and fatness on CHD risk status, correcting for potential confounding variables. Results: Our main findings were: 1) Relationships between fatne ss and CHD risk factors are invariably stronger than between fitness and th e same risk factors. For example, partially adjusted standardized regressio n coefficients for 12-yr-old boys revealed significant relationships betwee n all five CHD risk factors and fatness. compared with three of five for fi tness. The corresponding figures for 12-yr-old girls were three of five (fa tness) and one of five (fitness). Broadly similar results were apparent for 15-yr-olds. 2) Although relationships between fitness and CHD risk factors do not survive further adjustment for fatness, the relationships between f atness and CHD risk are more robust and are unaffected by further adjustmen t fur fitness. Conclusion: Our results indicate that the observed relations hips between C-R fitness and CHD risk status in adolescents are mediated by fatness, whereas the observed relationships with fatness are independent o f fitness. Primary prevention of CHD during childhood should therefore conc entrate upon preventing or reversing undue weight gain.