Screen time trajectories from 18 months to 3 years and dental caries at age 3 years: a population-based cohort study in Japan.

BACKGROUND

Screen habits change rapidly in toddlerhood, but whether changes in screen exposure are associated with early childhood caries and obesity remains unclear.

METHODS

We used linked routine child health check-up records at 18 months and 3 years in Okinawa, Japan (2014-2019). Children were categorized into four screen time trajectory groups based on routine screen time at 18 months (yes/no) and screen time >1 h/day at age 3 (yes/no). The primary analysis included children with no reported screen use at age 3 years as 0 h/day (≤1 h/day). Dental caries and obesity were assessed at the 3-year check-up. Multivariable logistic regression estimated adjusted odds ratios (aOR) and 95% confidence intervals (CI), adjusting for confounders and baseline caries or body mass index.

RESULTS

Among 71,438 children, those who newly exceeded 1 h/day between 18 months and 3 years had higher odds of dental caries at age 3 years than those who maintained low exposure (aOR 1.27; 95% CI, 1.12-1.45). Persistently high exposure was also associated with caries (1.11; 95% CI, 1.02-1.20). Findings were consistent in robustness analyses and were stronger for severe caries (aOR 1.55; 95% CI, 1.31-1.84) and caries counts (incidence rate ratio 1.29; 95% CI, 1.14-1.46). Screen time trajectory was not independently associated with obesity after accounting for baseline body mass index.

CONCLUSION

Escalation of screen time was associated with higher risk of dental caries at age 3 years. Trajectory-based monitoring at toddler health checks may support counseling to keep meals and toothbrushing screen-free.