Dose-response association between different screen time behaviors and cardiorespiratory fitness among elementary and junior high school students: A population-based cross-sectional study in a Japanese city.

BACKGROUND/

OBJECTIVE

Excessive screen time has been associated with lower cardiorespiratory fitness (CRF) in youth, but evidence on the dose-response association remains limited. This cross-sectional study examined screen time and CRF among elementary school (ES) and junior high school (JHS) students.

METHODS

Of 870 ES and 876 JHS students recruited in Unnan City, Japan, in 2023, the analytical sample comprised 664 ES students (aged 9-12 years; 51.8% boys) and 679 JHS students (aged 12-15 years; 47.6% boys). CRF was assessed by the 20-m shuttle run and expressed as z-scores. Screen-based behaviors (gaming and video viewing or social networking service [SNS] use) were assessed by questionnaire. Multiple linear regression and restricted cubic spline analyses were adjusted for sex, grade, breakfast consumption, sleep duration, and sports club participation.

RESULTS

Among ES students, gaming for 2-<4 h (B = -0.28, 95% CI: -0.53, -0.04) or ≥4 h (B = -0.43, 95% CI: -0.70, -0.16) was associated with lower CRF than no gaming, with an inverse trend (P for trend = 0.001). Similarly, ≥4 h of video/SNS use was associated with lower CRF (B = -0.33; P for trend = 0.001). Among JHS students, no individual category was significant, but both showed inverse trends (P for trend = 0.013 and 0.014, respectively). Restricted cubic splines showed no detectable non-linearity.

CONCLUSION

Longer recreational screen time was associated with lower CRF in both groups-significantly lower in higher categories among ES students and significant inverse trends among JHS students. Longitudinal and experimental studies are needed to establish causality.