This study aims to analyze the associations between sleep characteristics, including sleep opportunity, problems and social jetlag, and toddlers' adiposity. It is part of a larger research project involving 344 children (mean ± SD age of 23.6 ± 6.3 months). Children's length/height, weight and waist circumference were measured at childcare centers. Body Mass Index (BMI), weight-for-length/height, and waist-to-length/height were calculated and classified according to percentiles, serving as surrogates of adiposity. Sleep problems were evaluated through questionnaire. Sleep opportunity was reported by parents and defined as the difference between bedtime and wake-up time. Social jetlag was calculated based on sleep midpoints. Parental questionnaires provided sociodemographic characteristics. Total energy intake was determined from a two-day dietary record, and motor development was assessed using the Bayley-III scales. Generalized linear models were used in the analysis. We found that nighttime sleep opportunity on weekdays was inversely associated with BMI percentile (B = -5.57, 95 % CI -9.79 to -1.35), even with covariates included. Additionally, later bedtime on weekend days were associated with lower weight-for-length/height and waist-to-length/height (B = -4.16, 95 % CI -8.01 to -0.30, and B = -10.62, 95 % CI -15.38 to -5.87, respectively), even when adjusted for potential confounders. Later bedtime on weekdays was associated with lower waist-to-length/height (B = -8.85, 95 % CI -14.95 to -2.74). Social jetlag was associated with lower waist-to-length/height (B = -7.19, 95 % CI -13.47 to -0.90). Future research is needed to clarify these associations and to encourage lifestyle-based interventions aimed at optimizing sleep patterns within this age group.
