Exploring the relationships between extreme body mass index and pain, somatic health, and psychiatric disorders in adolescents: a multinational analysis of general population data

Abstract Background Both high and low body mass index (BMI) in adolescence have been linked to physical and mental health problems, but these outcomes are rarely examined together. This study examined the associations between BMI categories and self-reported pain, somatic diseases, and psychiatric disorders among adolescents. Methods A total of 5,132 adolescents from five countries (United States, Serbia, Sweden, Morocco, and Vietnam) participated in an online survey conducted between September 2020 and February 2021 as part of the Mental and Somatic Health Without Borders project. After excluding incomplete responses, data from 4,742 participants (mean age = 16.69 ± 1.02 years; 62.1% girls) were analysed. BMI categories were defined using WHO BMI-for-age z-scores, with normal BMI as the comparison group. Group differences were assessed using non-parametric and exact tests with multiple-comparison correction, followed by multivariable regression adjusted for age, gender, and country of residence. Results Most participants had normal BMI (approximately 88%); 8.2% had overweight, 3.7% obesity, and 0.34% ( n = 16) underweight. In adjusted analyses, adolescents with obesity had higher pain intensity and higher odds of reporting pain “all the time” than those in the comparison group. Overweight and obesity were associated with higher odds of asthma, while obesity was additionally associated with allergies and overweight with thyroid disease. Regarding psychiatric outcomes, overweight and obesity were associated with higher odds of anxiety, whereas obesity was additionally associated with higher odds of depression and attention-deficit/hyperactivity disorder. Findings involving underweight were less conclusive because of the small number of underweight adolescents and sparse events. Conclusion Higher BMI categories were associated with distinct patterns of somatic, pain-related, and psychiatric outcomes among adolescents. Obesity showed the broadest pattern of associations, including greater pain burden and higher odds of several somatic and psychiatric conditions. These findings support considering BMI within a broader assessment of adolescent physical and mental health and highlight the value of integrated preventive strategies.