Underweight in 14 to 16 year-old girls and boys: prevalence and associations with physical activity and sedentary activities

Introduction and objectives. Underweight is associated with increased mortality of adults when compared to normal weight or overweight individuals. Studies of associations between underweight and physical activity levels in adolescents are sparse. The aim of this study was to determine the prevalence of underweight amongst 14 to 16 year-old girls and boys in tandem with the levels of physical activity and time spent in sedentary activities. The results were compared to those observed in normal weight and overweight adolescents. Material and methods. This study included 1702 girls and 1547 boys aged from 14 to 16 years from twelve gymnasium schools in Poznan (Poland). Based on BMI values, the participants were assigned to the following categories: a) underweight, b) normal weight, and c) overweight. The levels of physical activity, participation rates in physical education classes and the time spent in sedentary activities were determined by means of questionnaire survey. Results. The fraction of underweight girls amounted to 11.6% and was similar to the percentage of obese girls (14.6%). The fraction of underweight boys was 7.0%, and was markedly lower than the percentage of overweight boys (17.0%). Underweight and overweight boys were characterized by significantly lower levels of physical activity compared to normal weight participants (p <=.001). Both in girls and in boys, the prevalence of underweight and overweight was not significantly associated with the time spent in various sedentary activities. Conclusions. Underweight occurs in relatively high fraction of girls and boys. Underweight is associated with lower levels of physical activity in boys. The prevalence of underweight among adolescents is not associated with time spent in sedentary activities.