This study revealed the link between short sleep duration and overweight/obesity in adolescents of Fuzhou, China. After adjusting socio-demographic status, lifestyle factors, and mental health, there was a negative correlation between short sleep duration and overweight/obesity among male children.
The prevalence of overweight or obesity in our study was 19.2%, which was higher than the national average [2]. Moreover, our findings demonstrated the differences among gender, age and region, which were similar with the Report on Childhood Obesity in China [32]. The prevalence of obesity showed decline with the elevation of the ages, which may be possibly related to physical development and attention to their appearances[33, 34].
The prevalence of obesity in male children was significantly higher than that of female children. In addition, the prevalence of short sleep duration in adolescents showed strike increase with age. About 92.4% of adolescents in high school suffered from short sleep duration. Study pressure, especially pressure from the college entrance examination, may contribute to such a high prevalence.
Our study revealed that short sleep duration was negatively related to overweight/obesity which was consistent with previous study showing that sleep deficiency seemed to parallel the increased prevalence of obesity[35]. Meanwhile, it could be an independent risk factor for obesity[10, 36, 37]. One study provided causal evidence on the relationship between short sleep duration and weight gain in the population-level [38]. Moreover, Krietsch et al reported that there was a U-shaped correlation between those with short sleep duration and obesity only in the female children [39]. These differences may be related to the physiology of adolescence between female and male.
To date, little is known about the relationship between sleep and obesity. Sleep duration involved in the regulation of cerebral function such as controlling the appetite, which could lead to over-eating in an obesogenic environment [40]. The homeostatic control of appetite was achieved by complex interactions among numerous neuroendocrine hormones [41]. Many pivotal hormones (e.g. insulin, leptin, cortisol and ghrelin) [42] may involve in the correlation between sleep and obesity. Even after adjusting the BMI, sleep duration was negatively correlated with circulating leptin [43]. Eptin pathway could explain the key mechanism via modificatory effects [44]. Under some circumstances, the short sleep duration could lead to disruption of insulin, leptin, cortisol and ghrelin expression [45, 46]. After a period of sleep loss, people could experience a 24% increase in hunger with largely whetting the appetite for high carbohydrate foods [45]. In our study, students with short sleep duration spent more time on night snack than those with adequate sleep, which may lead to weight gain. Fatigue caused by short sleep duration may result in reduced physical activity, which then promoted the weight gain [47, 48]. In this study, adolescents with adequate sleep did more exercise of moderate-intensity than those with short sleep duration.
Circadian Locomotor Output Cycles Kaput (CLOCK) genes involved in regulation of diurnal rhythm, and their effects on neuroendocrine systems might have an impact on obesity [49]. The variants of CLOCK gene was related to sleep duration [50], as with calorie intake [51], metabolic syndrome [52], and obesity [53]. Meanwhile, methylation of CLOCK gene was associated with carbohydrate intake, total energy intake, insulin resistance, and BMI [54]. REV-ERBα rs2071570 and rs2071427 were related to BMI and sleep duration in male children, confirming the association of the REV-ERBα gene with human obesity, mainly in males [55]. In line with our findings, this theory supported a negative correction between sleep duration and overweight/obesity among male children [56].
Obesity is not simply related to biology and behavior, but also to the our social context [57]. Social support from friends and awareness/internalization of thinness ideals were significantly related to odds of overweight/obesity in youth. Such association varied by age and sex, and persisted after control for intra-familial factors such as overall family support/function, diet and activity specific support [58]. A cross-sectional study on societal risk factors for overweight and obesity in women in Zimbabwe showed that the key social factors associated with overweight and obesity were older age, wealthy and the use of hormonal contraception. Besides, a higher education and being Christian also increased the risk of obese and overweight, respectively [59]. Some home environment related factors may increase the incidence of overweight/obesity among children, such as sleeping too late that may lead to inadequate sleeping and increased opportunity for taking food in night [60]. Less daytime care by mothers and shorter sleep duration were associated with increased risk of becoming overweight during childhood [61].
In this study, there were no statistical differences between the short sleep duration and overweight/obesity in the female children, however, the lower CI (95% CI 0.99-1.93) was very close to significance. It appeared that this association was just smaller than what was observed for males. It may be that the stratified analysis lacked statistical power. In our subsequent study, studies of a large sample size involving more social variables are required to investigate the effects of short sleep duration on the overweight/obesity in female children.
A large and representative sample was included in the survey. Meanwhile, we analyzed a wide range of covariance to verify the relationships between sleep duration and overweight or obesity by adjusting potential confounding factors correlated with overweight or obesity. Nevertheless, there are some limitations in our study. First, causal inference will be limited in the cross-sectional design, although there are several theories supporting our findings. Second, the determination of sleep duration was reported by the students themselves, which was a limiting factor. Indeed, the facilities may contribute to the reduction of the errors to some extent, however, it was a challenge for the promotion of the facility as the sample size was too large. In the subsequent study, representative samples will be selected for the monitor of the sleep duration of the subjects including sleep quality. Third, the impact of prolonged sleep duration on overweight or obesity among adolescents was not explored in our study, as we laid emphasis on the risk of overweight or obesity induced by short sleep duration in middle-school students. Then we will focus on the effects of long sleep duration on the overweight and obesity in the students. Fourth, the psychologic status of the subjects when self-reporting may lead to some bias of the results. In a follow-up study, qualified mental scales will be required to evaluate the psychologic status including depression and sorrow, which can correct the effects of psychologic variables on overweight and obesity.