Background: Underweight among adolescents is an important clinical and public health issue. It is associated with adverse health outcomes throughout the life-span and may reflect food poverty, unhealthy eating habits, or some underlying health conditions.
Objective: To study prevalence and trends in underweight among adolescents 1998-2018, to examine social inequality in underweight, and whether social inequality changed over time.
Methods: Data were derived from 6 cross-sectional school surveys from The Health Behaviour in School-aged Children study in Denmark. The study included 11-, 13-, and 15-year-old schoolchildren in random samples of schools in 1998, 2002, 2006, 2010, 2014, and 2018 (n = 22,177). Underweight was determined by body mass index-for-age thinness grade 2-3 (the Cole and Lobstein method). Socioeconomic status was determined using occupational social class (the Danish OSC Measurement).
Results: The overall prevalence of underweight was 3.1% among boys and 5.3% among girls (P < 0.0001) and decreased by age (P < 0.0001) among both boys and girls. The prevalence of underweight was almost stable from 1998 to 2018. There was no observed absolute or relative social inequality in the prevalence of underweight among boys or girls.
Conclusion: The prevalence of underweight in 11- to 15-year-olds was significantly higher among girls than boys. The prevalence remained stable from 1998 to 2018. There was no significant association between SES and prevalence of underweight. It is important to elucidate the underlying causes of underweight such as malnutrition, eating disorders, eating problems, loss of appetite, chronic diseases, insufficient knowledge of nutrients effects on bodily functions, and persistent pain.
Keywords: Denmark; adolescents; socioeconomic status (SES); thinness; trend study; underweight.
Underweight among adolescents is an important clinical and public health issue as it may reflect food poverty, unhealthy eating habits, or some underlying health problem. The aim was to study prevalence and trends in underweight among adolescents 1998–2018 and to examine social inequality in underweight. We used data from 6 cross-sectional school surveys from Denmark. Across all surveys, the number of participants was 22,177 11-, 13-, and 15-year-old students. The prevalence of thinness grades 2 and 3 were taken as indicators of underweight and were 3.1% among boys and 5.3% among girls. This prevalence was almost stable from 1998 to 2018. Contrary to overweight, which is usually more prevalent in lower socioeconomic groups, underweight was not associated with socioeconomic status. There were 2 exceptions: the prevalence of underweight among girls was highest in those from high socioeconomic groups in1998, while the prevalence among boys was highest in those from low socioeconomic groups in 2018. Underweight conditions in adolescents need careful medical examinations to elucidate the underlying causes of underweight, for example, malnutrition, eating disorders, eating problems, loss of appetite, voluntary uptake of fad diets, chronic disease, insufficient knowledge of nutrients that impact their bodily functions, mental health problems, and persistent pain.
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