Associations of smartphone use duration and loneliness with depressive symptoms among Korean adolescents: a nationally representative cross-sectional study

BackgroundAdolescent depression is a major public health concern, yet the relative contributions of smartphone use duration and perceived loneliness remain unclear. This study examined their independent and comparative associations with depressive symptoms in a nationally representative sample of Korean adolescents.MethodsThis cross-sectional study analyzed data from 54,653 middle and high school students from the 2024 Korea Youth Risk Behavior Survey. Depressive symptoms were assessed using a single self-reported item. Weekday and weekend smartphone use (h/day) were modeled as continuous variables. Multivariable logistic regression analyses were conducted adjusting for sociodemographic factors, health behaviors, perceived stress, and anxiety symptoms. Nagelkerke pseudo-R2 was used to assess incremental explanatory value.ResultsWeekday smartphone use showed a small positive association with depressive symptoms (OR = 1.02, 95% CI 1.01–1.03). In contrast, perceived loneliness demonstrated a strong graded association: moderate loneliness (OR = 2.54, 95% CI 2.40–2.68) and high loneliness (OR = 4.74, 95% CI 4.43–5.07) were associated with substantially higher odds of depressive symptoms. The inclusion of loneliness increased the model's explanatory power (ΔNagelkerke R2 = 0.163). Weekend smartphone use showed a marginal inverse association (OR = 0.99, 95% CI 0.98–1.00).ConclusionsPerceived loneliness showed a substantially stronger association with depressive symptoms than smartphone use duration. These findings highlight the importance of addressing social isolation in adolescent mental health interventions, alongside promoting balanced and context-sensitive smartphone use.