Is sleep duration associated with childhood obesity? A systematic review and meta-analysis.

Obesity is a major public health epidemic worldwide in children and adults (1–6). The prevalence and severity of childhood obesity is dramatically increasing with a corresponding increase in the prevalence of obesity-related morbidities particularly those involving obstructive sleep apnea and metabolic and cardiovascular seque-lae (7). Prevention of childhood obesity is an urgent issue for public health, in par-ticular, in many industrialized countries and some transition societies. Nutrition and physical activity (PA) have been the major research focus on obesity preven -tion (8–11). However, most published findings of such interventions suggested little success in preventing childhood obe-sity (6,12), although some that focused on dietary or/and PA approaches have showed some desirable impact on BMI status (13). Other risk factors, such as sleep, may be related to obesity, although sleep behavior has received much less attention than dietary intake and PA (14,15).Sleep, like PA and diet, plays an impor-tant role in the growth, maturation, and health of children and adolescents by allowing for the diurnal rhythm of hor -mones related to growth, maturation, and energy homeostasis (16). A number of biological mechanisms have been pro -posed to link sleep duration and obesity (17). For example, one theory posits that children with short sleep have low caloric intake and expenditure, given that sleep deprivation often leads to changes in the structure of sleep stage and results in fatigue, daytime sleepiness, somatic and cognitive problems, and low activity lev-els (18,19). Previous studies indicate that sleep deprivation results in changes in lev -els of several hormones including leptin, ghrelin, insulin, cortisol, and growth hor-mone (20–22). These hormonal changes may contribute to energy imbalance and then lead to overweight or obesity.Recently, there is increasing epide-miological evidence suggesting a link between sleep duration and obesity in children (18,23–26), adolescents (27), and adults (28–30). In adults, some studies indicate a negative association between sleep duration and obesity/BMI in men and a U-shaped relation between sleep duration and BMI in women (29). Several epidemiological studies have examined the association between short sleep duration and obesity in children and adolescents (18,23–27,31–37), but the reported findings are inconsistent (18,32,35,37). A recent review summa-rized 13 studies that examined the asso-ciation between short sleep duration and obesity among children and adolescents, and recommended more sleep to pre-vent obesity (17). However, the review suffered from several limitations includ-ing misclassification of the design of some studies and included a study with adults as the primary age group (28). Several related previous studies were not included. Furthermore, new studies have been reported since the publication of the review. A major gap in the related litera-ture is that to our knowledge, no meta-analyses have been conducted to examine the overall association quantitatively and to test the possible differences by popula-tion groups such as age and gender.This study aimed to assess epidemio-logic evidence systematically on the relation between sleep duration and childhood obesity. We first performed a systematic review of all related studies and then conducted a meta-analysis based on cohort studies and cross-sectional studies in the general pediatric population.