Background and Objective: This study aimed to investigate the moderating role of screen time in the relationship between body mass index (BMI) and sleep duration in children and adolescents in Karaj. Given the increasing use of digital technologies and their potential impacts on health, this research sought to evaluate the association between screen time and health indicators in this age group.

Methodology: The study included 1338 children and adolescents aged 6 to 17 from Karaj. Weight and height were measured to calculate BMI. Information on screen time, sleep duration, age, gender, pubertal status, residence area, and socio-economic status was collected via a self-reported questionnaire. Multiple linear regression modeling was used for data analysis, adjusting all models for gender, age, pubertal status, residence area, and socio-economic status.

Findings: Results showed that although no direct association was found between BMI and sleep duration, screen time significantly moderated this relationship. Specifically, children and adolescents who spent more than 360 minutes per day on screens had higher BMI and shorter sleep duration. These findings suggest that screen time can act as a moderating variable in the relationship between BMI and sleep duration.

Conclusion: This study emphasizes that the more time children and adolescents spend on screens, the higher the likelihood of negative impacts on BMI and sleep duration. These findings highlight the need for interventions promoting healthy screen use and encouraging behaviors that support optimal sleep duration to mitigate potential negative effects on body weight and overall health.