Social jetlag is associated with body mass (BMI) in children aged 2-8years: A cross-sectional analysis.

Objective: Social jetlag is associated with higher body mass index (BMI) in adults, adolescents, and older children. However, no research to date has addressed social jetlag and body mass index in early childhood. This study investigated the association between social jetlag and BMIz in children aged 2-8years.

Methods: Cross-sectional data were leveraged from 1122 children (M=5.6±1.7years, 48.8% females) from the NIH Environmental influences on Child Health Outcomes (ECHO) study between 2016 and 2021. Sleep timing was parent-reported. Social jetlag was calculated as the absolute difference in weekend-weekday sleep midpoint. Objective measurements of children's height and weight were used to compute age- and sex-adjusted BMIz. Regression models tested the association between social jetlag and BMIz, adjusting for sociodemographic and sleep covariates.

Results: After controlling for age, sex, race and ethnicity, primary caregiver education, and average nighttime sleep duration, social jetlag was positively associated with BMIz (β=0.126, 95% CI: 0.004-0.249, p=.043). Children with ≥1-h social jetlag had higher average BMIz and had 66% higher odds of being overweight or obese (OR=1.66, 95% CI: 1.13-2.46, p=.01), compared with children with no social jetlag.

Conclusions: Social jetlag may contribute to higher BMIz in young children, similar to findings in older children, adolescents, and adults. At least 1 hour of social jetlag may increase children's odds of being overweight or obese. Future research is needed to test causality and whether reducing social jetlag can lead to healthy weight-related outcomes.