Association of smartphone use with abnormal social jetlag among adolescents in Korea before and after COVID-19

PURPOSE: This study aimed to use social jetlag to determine how smartphone overuse by adolescents before and after the COVID-19 pandemic might be associated with their circadian rhythm. METHODS: We used 2017 and 2020 Korea Youth Risk Behavior web-based Survey data and conducted a survey analysis on 100,976 adolescents. The dependent variable was abnormal social jetlag. Based on the times recorded by the survey, we calculated the weekday midpoint and weekend sleep time. The main independent variable was smartphone usage time (<2h/day, 2–3.9 h/day, 4–5.9 h/day, and ≥ 6 h/day). Multiple logistic regression and relative excess risk due to interaction (RERI) were performed. RESULTS: Abnormal social jetlag was most prevalent in male and female adolescents who used smartphones ≥ 6 h/day (adjusted odds ratio [AOR] = 2.60, 95 % confidence interval [CI] = 2.47–2.74). The longer the smartphone usage time, the higher the association with abnormal social jetlag. This association was more prominent in female adolescents. The additive interaction between longer smartphone usage time and post-COVID-19 year was statistically significant (total: RERI = 0.92, 95 % CI = 0.90–0.95; males: RERI = 0.83, 95 % CI = 0.80–0.87; females: RERI = 1.13, 95 % CI = 1.08–1.18). CONCLUSION: Our results clearly indicated that increased smartphone usage time tended to result in greater social jetlag, an association that was more pronounced in female. Moreover, the COVID-19 pandemic significantly strengthened this relationship. Further research is needed regarding the proper use of smartphones to ensure good sleep-in adolescents after the COVID-19 pandemic.