Cross-sectional associations of nighttime sleep and daytime nap duration with myopia in preschool children: the mediating role of body mass index

Objective: To investigate the associations of nighttime sleep and daytime nap duration with myopia in preschool children, and to examine the mediating role of body mass index (BMI). Methods: This cross-sectional study included 695 children aged 3-7 years. Sleep duration, demographics, family factors, and lifestyle were assessed via a self-administered questionnaire. Ophthalmic examinations followed national myopia screening guidelines. Multivariate logistic regression, restricted cubic splines, and mediation analysis were used to evaluate the associations and the mediating effect of BMI. A protective inflection point was identified at 38 min for daytime napping. BMI partially mediated the associations of daytime nap and nighttime sleep with myopia, accounting for 24.79 and 28.16% of the total effects, respectively. Conclusion: Both nighttime sleep and daytime nap duration were inversely associated with myopia risk in preschool children, with BMI playing a partial mediating role. Ensuring adequate nighttime sleep and appropriate daytime napping may represent an effective strategy for early myopia prevention.