Associations between health-related quality of life and body mass index in Portuguese adolescents: LabMed physical activity study

Background In adolescence there are several biological and physiological changes associated with overweight and obesity. Objective The purpose of this study was to analyze the associations between health-related quality of life (HRQoL) and body mass index (BMI) in adolescents. Methods This is a cross-sectional analysis of 957 Portuguese adolescents (446 girls and 511 boys) aged 12–18 years. A series of variables were collected: (a) HRQoL was assessed using the KIDSCREEN-10 questionnaire; (b) socioeconomic status (SES) was measured using the Family Affluence Scale; (c) body composition (weigh, height) were measured and BMI was calculated and, (d) pubertal stage was assessed with Tanner stages; (e) the 20-m shuttle-run was used to estimate cardiorespiratory fitness. Regression models and mediation analysis were performed to assess the association between HRQoL and BMI. Results HRQoL was significantly higher in boys than girls (p < 0.05). The prevalence of overweight and obesity was 23.5% and 6.7% in girls, and 21.3% and 5% in boys, respectively. HRQoL was inversely and significantly associated with BMI in boys (B = −0.130; p < 0.05) and girls (B = −0.148; p < 0.05) after controlling for age, pubertal stage and SES. Cardiorespiratory fitness act as a full mediator variable on the relationship between BMI and HRQoL in adolescents (p < 0.05). Conclusion Our results suggest that cardiorespiratory fitness acted as a full mediator in the relationship between BMI and HRQoL, in adolescents. Public health policies targeting a wealthy weight and an improved physical fitness level could be a strategy of particular interest for improving the HRQoL of adolescents.