Influence of study shift on the interrelationships among chronobiological factors, health practices, and anthropometry in adolescents

The mismatch between chronobiological predispositions and social demands makes it difficult for adolescents with an evening chronotype to maintain healthy habits. This study aimed to explore the interrelationships among chronobiological factors, health practices, and anthropometry in adolescents attending morning and afternoon class shifts. In this cross-sectional study, 925 adolescents (14-19 years old) completed an online questionnaire covering food practices, chronotype, sleep duration, social jetlag, screen time, socioeconomic data, physical activity, school shift, and anthropometric measurements. The interrelationships among these variables were analyzed through structural equation modeling using six path models. Food practices were categorized into "complete meals" (breakfast, lunch, dinner, and bean consumption) - as healthy practices, "unhealthy foods" (sweets, fried snacks, soft drinks, salty ultra-processed foods, and fast food) and "vegetables and fruits," stratified by shift (morning or afternoon), with body mass index by age (BMI/age) as the main outcome. Among students in the morning shift, reduced sleep time was directly associated with increased BMI/age, while longer screen time was negatively associated with complete meal practices and physical activity. In the afternoon shift, a greater tendency towards an evening chronotype among adolescents was associated with reduced complete meal practices and lower regular fruit and vegetable consumption. Sleep duration was positively associated with a greater likelihood of a complete meal practices and regular fruit consumption. Moreover, longer screen time was positively associated with unhealthy food consumption. In both shifts, physically active adolescents consumed fruits more regularly. The practice of regular consumption of complete meals, fruits, vegetables, or unhealthy foods, in addition to being directly influenced by chronotype and other variables, was also influenced by shift. Adolescents with shorter sleep duration were at a higher risk of being overweight, suggesting a direct influence of sleep on anthropometric measurements. Our findings underscore the importance of considering study shifts in future interventions.