Childhood obesity and sleep disorders have become a global public health priority over the past decade (1, 2). Studies indicate that insufficient sleep among children is prevalent worldwide, with regional variations. For instance, 13.3% of children aged 6–12 years in mainland China experience sleep deprivation on school days, 40% of preschoolers in Hong Kong, China, fail to meet recommended sleep duration, and 23.6% of children aged 1–14 years in Spain exhibit short sleep duration (3–6). Notably, data from the past decade reveal a parallel and prospectively associated trend between rising childhood obesity rates and declining average sleep duration (7, 8). As of 2016, WHO data revealed that approximately 340 million children and adolescents worldwide were affected by overweight or obesity (9). Concurrently, China’s 2020 national survey reported overweight and obesity rates of 11.1% and 7.9%, respectively, among children aged 6–17 years (10), with a persistently escalating trend observed in low-income countries (11).

Within growth trajectories, early-life exposure to obesogenic environments is critical for the development of obesity (12). In addition to common influencing factors, other unhealthy behaviors, such as poor sleep quality, insufficient sleep duration (13), reduced physical activity (14), and increased screen time (15), are associated with an elevated risk of weight gain and may have long-term negative consequences (11, 16, 17). The longitudinal study demonstrated that poor sleep habits at the age of 1 significantly increase the risk of being overweight at the age of 8 (18). Moreover, suboptimal sleep quality may exacerbate obesity by disrupting energy metabolism homeostasis (19). However, existing research findings remain inconsistent: while some studies have found a significant negative correlation between sleep duration and obesity (20), others have not observed a significant association, possibly due to sample size limitations or low reporting rates of sleep problems (21). Furthermore, the interaction between sleep-related variables—such as duration, quality, and bedtime—remains unclear, particularly in the context of Chinese children, on whom systematic evidence is lacking (22).

International health organizations have issued age-specific sleep recommendations for children, reflecting variations in sleep requirements across developmental stages: The 2019 WHO guidelines suggest that children under the age of 5 require 10–13 h of high-quality sleep per day (23), while the American Academy of Sleep Medicine recommends 9–12 h of sleep per day for children aged 6–12 y (24). In China, the Ministry of Education mandates that primary school students sleep no less than 10 h per night and go to bed no later than 21:20. However, in reality, children often face multidimensional sleep issues, such as having good sleep quality but insufficient duration or experiencing delayed bedtimes. The synergistic effects of these factors on weight-related indicators have yet to be elucidated.

This study, based on children from southern China, aims to address the following scientific questions: (1) Utilizing the Children’s Sleep Habits Questionnaire (CSHQ), along with a parent-reported children’s characteristics survey, we will assess whether sleep quality, duration, and bedtime independently or synergistically influence children’s weight development; (2) employing an additive model, we will quantify the interaction effects among sleep variables to provide evidence for the development of targeted intervention strategies. The findings of this study will fill gaps in the existing literature and serve as a reference for the evidence-based revision of children’s sleep health guidelines.

Children, as a focal point of societal and familial concern, garner significant attention in their growth and development. Historically, children’s weight has been a primary focus of Early Childhood Development (ECD) (28), while in the past decade, children’s sleep hygiene has emerged as a hot topic in public health. The exploration of the relationship between sleep and children’s weight development is also a pressing issue awaiting clarification by researchers. This study focuses on the combined effects of sleep quality and sleep habits on children’s weight development.

Among the 19,047 children included in this study, the prevalence of overweight or obesity was higher in boys than in girls. Significant differences were observed between normal weight and overweight or obese children across age groups, urban–rural distribution, and maternal education levels. Preliminary analyses revealed marked disparities in sleep quality and bedtime among different weight groups for sleep-related independent variables, consistent with prior studies by Schultz et al. and Covington et al. (29–31). Further exploration of risk factors demonstrated that, in the adjusted multivariate model, later bedtime (after 22:00) and prolonged screen time (>2 h/day) were both associated with elevated risks of childhood overweight or obesity (OR = 1.186, 95% CI: 1.065–1.320; OR = 1.121, 95% CI: 1.010–1.245). However, suboptimal sleep quality exhibited a protective association with childhood overweight/obesity in this model (OR = 0.825, 95% CI: 0.759–0.889). Jebeile et al. noted in The Lancet that poor sleep quality may exacerbate energy regulatory dysfunction, potentially promoting weight gain (19). However, studies by Michels et al. and Cespedes et al. reported divergent findings, indicating no statistical association between sleep quality and obesity-related behaviors (32, 33). Although extensive research has explored mechanisms linking poor sleep quality to obesity, no definitive evidence currently establishes poor sleep quality as a causal factor for overweight or obesity.

Sleep duration and bedtime are two fundamental components of the sleep process and have been extensively examined in studies on children’s sleep hygiene. In the model presented in Table 3, sleep duration, treated as a continuous variable, demonstrated a statistically significant association with the outcome variable. It was identified as a protective factor against childhood overweight and obesity, with the risk of adverse outcomes decreasing as sleep duration increased. This finding aligns with the results of most existing studies (30, 32, 34). Conversely, bedtime demonstrated a statistically significant association in the model and was identified as a risk factor for overweight and obesity. A study by Anderson et al. on American children revealed that delayed bedtime was associated with elevated adolescent obesity prevalence. Specifically, compared with children maintaining early and regular bedtimes during preschool years, those with later bedtimes exhibited a multivariable-adjusted relative risk of 0.48 (95% CI: 0.29–0.82) for adolescent obesity (35). Mechanistically, research investigating the adverse effects of late bedtime on weight development found that insufficient sleep duration caused by delayed bedtime may lead to postponed mealtimes (mean delay: 35 min, 95% CI: 16–53, p < 0.001) and increased caloric intake (β = 131.51, 95% CI: 87.47–175.56, Z = 5.85, p < 0.001) (36). These findings underscore the potential negative impact of bedtime on childhood weight outcomes, emphasizing the necessity of addressing both sleep duration and sleep timing in obesity prevention strategies.

To further analyze and visually present the relationship between sleep duration, bedtime, and weight development, this study employed RCS models, combined with logistic regression, to explore the non-linear associations among variables. Compared with the reference point of 10.5 h defined in this study, children with shorter sleep duration exhibited a higher risk of adverse outcomes. This finding is consistent with the study by Tuerxun et al., which identified a significant statistical correlation between shorter sleep patterns and both general and abdominal obesity among children aged 3–6 years in Wuhan (16). Similarly, a cohort study on the development of Japanese children demonstrated that children with shorter sleep duration at 2.5 years old had a higher risk of obesity at 5.5 years old, with a more pronounced effect as sleep duration progressively decreased, indicating a trend association (37). In contrast, in the RCS model results for bedtime, fluctuations in the odds ratio were observed. Therefore, in this study, participants were stratified based on bedtime, and an additive interaction model was applied to comprehensively analyze the combined effects of sleep duration and bedtime, as well as the interaction between sleep duration and sleep quality, on childhood overweight and obesity.

Existing studies predominantly utilize standardized instruments such as the Brief Infant Sleep Questionnaire (BISQ-E) (38) and the CSHQ (39) to assess pediatric sleep quality. In this study, sleep quality was evaluated by using the CSHQ. Additive interaction model analyses demonstrated that children with sleep problems but maintaining moderate (9–11 h) or extended (>11 h) sleep durations exhibited protective associations against overweight or obesity compared with those with optimal sleep quality (OR = 0.814, 95% CI: 0.733–0.905; OR = 0.759, 95% CI: 0.678–0.857, respectively). This paradoxical association may reflect compensatory mechanisms, whereby extended sleep duration in children categorized with poor sleep quality offsets its detrimental impacts.

Internationally recognized guidelines from the World Health Organization (WHO), the National Sleep Foundation, and the American Academy of Pediatrics recommend age-specific sleep durations (preschoolers: 10–13 h; school-aged children: 9–11 h; adolescents: 8–10 h) (40) and bedtimes (preschoolers: 19:00–21:00; school-aged children: 19:00–22:00; adolescents: 20:00–23:00) (24). Using children meeting these recommendations as the reference group, adjusted analyses revealed distinct risk patterns: late bedtime (after 22:00) elevated overweight or obesity risk among children with moderate sleep duration (OR = 1.214, 95% CI: 1.069–1.379), whereas early bedtime (before 21:00) reduced risk (OR = 0.853, 95% CI: 0.765–0.951). Insufficient sleep duration (<9 h) consistently increased risk regardless of bedtime. Notably, extended sleep duration (>11 h) with early bedtime retained protective effects against abnormal weight outcomes, yet failed to mitigate risks associated with late bedtime (OR = 0.983, 95% CI: 0.695–1.392).

Despite these novel findings, several limitations should be acknowledged. First, the questionnaires in this study primarily focused on children’s sleep and growth parameters, omitting parental BMI data, which may lead to residual confounding by unmeasured genetic factors. Meanwhile, the data rely on parental reports, which are inherently subject to recall bias. Second, the cross-sectional design with single time-point data precludes causal inference, providing only evidence of statistical associations. To address these limitations, our team is establishing the Hainan Island Birth Cohort (HIBC) to longitudinally validate potential causal relationships.

This population-based study of 19,047 children in southern China, focusing on multidimensional sleep patterns (duration, quality, and timing), reveals the following three pivotal insights into pediatric overweight or obesity:

Sleep duration and bedtime synergy: Short sleep duration (<9 h) and late bedtime (after 22:00) independently and synergistically elevate obesity risk (OR = 1.186 and 1.121, respectively), while adherence to age-specific sleep guidelines (9–11 h with bedtime before 21:00) confers protection (OR = 0.853, 95% CI: 0.765–0.951).

Non-linear dose–response: Restricted cubic spline analyses revealed a non-linear relationship, where obesity risk escalates markedly below 9 h of sleep, despite partial risk attenuation with extended sleep (>11 h).

Sleep quality paradox: Suboptimal sleep quality paradoxically associates with reduced obesity risk (OR = 0.825, 95% CI: 0.759–0.889), likely mediated by compensatory prolonged sleep duration offsetting quality deficits.

These findings underscore sleep duration and bedtime as modifiable targets for obesity prevention, while highlighting the complexity of the role of sleep quality’ in weight regulation.