Habitual sleep variability, mediated by nutrition intake, is associated with abdominal obesity in adolescents

Highlights

• Habitual sleep duration is not associated with abdominal obesity.

• Higher habitual sleep variability is significantly related to abdominal obesity.

• Excessive energy intake is a mediating factor in the association.

• Establishing a regular sleep pattern may reduce the risk of abdominal obesity.

Abstract

Objective

To investigate habitual sleep duration (HSD) and habitual sleep variability (HSV) in relation to abdominal obesity and nutrient intake as mediating factors in adolescents.

Methods

We analyzed data from 305 adolescents who participated in the Penn State Child Cohort follow-up examination. An actigraphy device was used for seven consecutive nights to calculate HSD and HSV. Abdominal obesity was assessed by dual-energy x-ray absorptiometry. The Youth/Adolescent Food Frequency Questionnaire was used to obtain daily total caloric, protein, fat, and carbohydrates intakes. Linear regression models were used to associate HSD and HSV with abdominal obesity and to qualitatively identify mediating factors. The mediating effect was quantitatively estimated by mediation models.

Results

After adjusting for major covariates and HSD, higher HSV was significantly associated with abdominal obesity measures. For example, with 1-hour increase in HSV, android/gynoid fat ratio and visceral fat area increased by 0.02 cm² (standard error = 0.01, p = 0.03) and 6.86 cm² (standard error = 2.82, p = 0.02), respectively. HSD was not associated with abdominal obesity in HSV-adjusted models. Total caloric, fat, and carbohydrate intakes were significant mediating factors. For instance, 20% of the association between HSV and visceral fat can be attributed to carbohydrate intake.

Conclusions

Higher HSV, not HSD, is significantly associated with abdominal obesity, which can be partially explained by increased caloric intake, especially from carbohydrate, in adolescents. This study suggests that more attention should be paid to establish and maintain regular sleep patterns in adolescents.

Introduction

The worldwide epidemic of overweight and obesity among children is of great concern, as childhood overweight and obesity track into adulthood [1]. It has been reported that obese children are approximately seven times more likely to become obese adults compared to normal-weight children [2]. Previous literature has also demonstrated associations between childhood obesity and increased risk of metabolic alterations and disease, such as insulin resistance, dyslipidemia, and metabolic syndrome [3], [4]. More important, excessive accumulation of adipose tissue in the abdominal region is an independent and more cardiometabolically relevant risk factor than general obesity, as measured by body mass index (BMI). For example, visceral fat accumulation is associated not only with quantitative changes in serum lipid but also with qualitative changes in lipoproteins, such as small dense low-density lipoproteins (LDL), and conveys greater insulin resistance than other adipose tissues [5].

In parallel with the marked increase in the prevalence of obesity, sleep deprivation and sleep disturbances have become a frequent complaint. In an analysis carried out by the U.S. Centers for Disease Control and Prevention (CDC) in 2009, 35.3% of U.S. adults had less than seven hours of sleep per night, compared with approximately 29% in the 2004–2006 National Health Interview Survey [6], [7]. Previous studies also indicated that self-reported short sleep duration and insomnia were prevalent in adolescents and young adults [8], [9]. Several studies reported an association between subjectively measured short sleep duration and obesity in both children and adults [10], [11], [12], [13]. Since subjectively measured short sleep duration has a weak correlation with objectively measured sleep duration [14], it can be argued that subjectively measured sleep duration may serve as a surrogate of stress, anxiety, and depression [15]. Within this theoretical framework, previous studies reported associations between anxiety, depression, emotional stress, and obesity [16], [17], [18]. Therefore, the observed association between subjectively-measured short sleep duration and obesity may be confounded by participants' psychological conditions [15], [19]. On the other hand, the relationship between objectively measured sleep duration and obesity has been inconsistent [19], [20], [21], [22], [23].

Because of the improvement and availability of actigraphy for multiple nights of sleep measurements, objectively measured habitual sleep pattern, represented by habitual sleep duration and intraindividual variability of sleep duration, has been used in the sleep field [24], [25]. Although the habitual sleep duration is an indicator of the average length of sleep, intraindividual variability focuses on the individual's sleep–wake rhythm. The study of the variability of sleep duration could provide new insight into sleep research. However, little is understood regarding the association between sleep duration variability and obesity. Recently, Kjeldsen et al. reported that both habitual sleep duration and sleep duration variability were associated with dietary risk factors for obesity in Danish school children [26]. Specifically, in a cross-sectional analysis of 676 adolescents, these investigators found that short sleep duration and high sleep variability were related to increased consumption of energy-dense food and sugar-sweetened beverages. Therefore, it is plausible that habitual sleep pattern is associated with excessive food and energy intake and consequently is related to obesity.

Therefore, this study was designed to investigate the associations between objectively measured habitual sleep duration (HSD), habitual sleep variability (HSV), and abdominal obesity in a population-based sample of adolescents. Our secondary objective was to examine the potential mediating role of energy intake in the habitual sleep and abdominal obesity relationship.