The purpose of this review is to provide a comprehensive update of epidemiologic studies that have assessed the association between sleep and obesity risk. Data suggest that short sleep is associated with an increased risk for being or becoming overweight/obese or having increased body fat. Late bedtimes are also a risk factor for overweight/obesity. Findings also suggest that changes in eating pathways may lead to increased body fat. Future experimental studies are needed to enhance our understanding of the underlying mechanisms through which sleep may play a role in the development and maintenance of childhood obesity.
Pediatric obesity is considered an epidemic, with 32% of US children and adolescents aged 2 to 19 years considered overweight or obese in 2007 to 2008. The medical and psychosocial risks associated with being overweight and obese as a child or adolescent have been well documented. Multiple studies have demonstrated the increased risk for type 2 diabetes and several cardiovascular disease risks, including elevations in cholesterol, diastolic and systolic blood pressure, fasting insulin levels, and triglycerides. Children and adolescents who are overweight and obese report lower health-related quality of life compared with their normal-weight peers, and may be at increased risk of poorer self-esteem, greater body dissatisfaction, and increased peer teasing. The importance of addressing this epidemic is underscored by several national policy efforts and by the proposed goals for Healthy People 2020.
Given the precipitous rise in pediatric obesity and its associated risks, increasing attention has been paid to efforts to enhance prevention and treatment approaches. Current prevention approaches have demonstrated variable impact on weight outcomes with some efficacy shown for school-based approaches that combine diet and physical activity. Several intervention approaches for children and adolescents who are overweight and obese have demonstrated efficacy, including those that combine dietary and physical activity prescriptions with the use of effective behavioral strategies. In adolescents, both use of weight-loss medication and surgical approaches show some promise. However, each of these approaches has limitations and, despite their effectiveness, often do not help children and adolescents achieve nonobese status. Thus, it is imperative to identify novel targets to enhance current treatment approaches.
Several factors suggest that enhancing children’s sleep may be an effective strategy for preventing and treating pediatric obesity. Over the past 20 to 30 years, as rates of pediatric obesity have climbed, children’s nocturnal sleep duration has declined. Data from the 2004 National Sleep Foundation’s Sleep in America poll show that the mean sleep length for school-aged children (first to fifth grade) is 9.4 hours per night. These data are in contrast to recommendations by sleep experts that children in this age group should obtain 10 to 11 hours per night. Thus, children may not be achieving sufficient sleep length.
Experimental studies with adults have documented physiologic and behavioral changes in response to sleep deprivation, which, if chronic, may promote weight gain. The secretion of growth hormone, prolactin, cortisol, thyrotropin, and insulin, are influenced by sleep. For example, studies suggest that sleep restriction leads to decreased circulating leptin and increased ghrelin, both of which are associated with increased hunger, appetite, motivation to eat, and food intake. Further, more recent experimental studies with adults have demonstrated increases in caloric intake from both snack foods and from main meals when sleep is restricted, suggesting that less sleep may increase the risk of obesity via neuroendocrine changes that increase food intake. Finally, although less is known in this regard, it is hypothesized that sleep deprivation may also lead to changes in physical and sedentary activities, which could promote weight gain. Limited support for this hypothesis comes from studies with adults that have demonstrated subsequent decreases in activity level following sleep deprivation.
To the authors’ knowledge, no experimental studies involving the manipulation of sleep in children and weight-related outcomes have been reported (although there are ongoing trials). However, there are considerable epidemiologic data with children and adolescents examining the association between sleep duration (typically nocturnal sleep) and weight status. Findings from both cross-sectional and prospective studies, although limited by their inability to demonstrate causation (ie, that less sleep at night leads to increased weight status), are important for helping to shape our understanding of the potential role that sleep may play in the current obesity epidemic. Prospective studies, in particular, help to establish temporal relationships between sleep and pediatric obesity. The purpose of this review is to provide a comprehensive update of epidemiologic studies that have assessed the association between sleep and obesity risk. Although obstructive sleep apnea is also associated with obesity risk, it is beyond the scope of this review. The reader is referred to Ievers-Landis and Redline as well as the article by Whitmans and Young in this special issue for a more comprehensive review. To build upon previous reviews, this review includes information on anthropometric indices (ie, waist circumference, percent body fat) other than body mass index (BMI) and findings regarding sleep timing and quality (as opposed to only focusing on sleep duration), and reviews findings regarding possible mediators of the sleep-weight relationship.
Methods
A systematic search for publications was performed using the PubMed database that included published studies through July 2010. Combinations of key words specific to sleep (eg, sleep and sleeping), weight status (eg, BMI, overweight, obesity, adiposity, weight, fatness, food diet, and energy expenditure), and childhood and adolescence (eg, child, children, adolescent, adolescence) were used. In addition, reference lists of relevant articles and previously conducted relevant review articles/meta-analyses were reviewed to identify additional studies. Only studies that focused on children and adolescents (ie, birth to 18 years of age) and represented original empirical work (ie, reviews and editorials were excluded) were included in the present review. Questions regarding inclusion of studies were decided by consensus. This process resulted in the inclusion of 38 studies (with 2 additional duplicates) in the present review.
Results
Sleep Duration and Obesity Risk
Table 1 presents findings from studies that assessed the association between sleep duration and obesity risk in children and adolescents. It represents 30 studies from 16 countries. For ease of comparison, studies presented in Table 1 are those in which main findings are presented as odds ratios. Two groups published subsequent studies using the same data set, but controlling for additional confounding variables. These subsequent studies were consistent with initial findings and are referenced as footnotes to Table 1 . The majority of studies present cross-sectional findings (N = 24), with 6 studies assessing the association between sleep duration and weight status prospectively. As can be seen in the table, the majority of studies assessed the construct of sleep duration exclusively through parent or self-report (N = 28) with 2 additional studies assessing sleep length via actigraphy. In contrast, the majority of studies (N = 27) used measured height and weight to calculate body mass index in children with only 2 studies using parent or self-report, and one additional study in which it was unclear whether caretaker report or measured height and weight were obtained.
| Study Country | Sample Characteristics | Sleep Measure and Reference Value | Measure of BMI Status a | Confounders Controlled | Main Findings |
|---|---|---|---|---|---|
| Cross-Sectional Studies | |||||
| Locard et al, 1992 France | 5 y old (N = 1031) | Caretaker-report Referent ≥11 h | Measured height and weight; weight-for-height and sex Zscore >2 = OB | — | OB: <11 h: OR = 1.4 (1.0–2.0) |
| Sekine et al, 2002 b Japan | 2.5–4.3 y (N = 8941) | Caretaker-report (24-h sleep) Referent ≥11 h | Measured height and weight; OB: age/sex BMI cut-off points by Cole et al | Age, gender, parental OB, and outdoor playing time | OB: <9 h: N/S 9–10 h: ORadj = 1.34 (1.05–1.72) 10 –11 h: N/S |
| Sekine et al, 2002 b Japan | 6–7 y (N = 8274) | Caretaker-report (24-h sleep) Referent ≥10 h | Measured height and weight; OB: age/sex BMI cut-off points by Cole et al | Age, sex, parental OB, PA, TV watching, frequency of breakfast, and frequency of snack | OB: 9–10 h: ORadj = 1.49 (1.08–2.14) 8–9 h: 1.89 (1.34–2.73) <8 h: 2.87 (1.61–5.05) |
| Von Kries et al, 2002 Germany | 5.0–6.99 y (N = 6645) | Caretaker-report (WD sleep) Referent ≤10 h | Measured height and weight; OW: age/sex BMI >90th centile, OB >97th centile based on local norms | Parent education, parent BMI, birth weight, first year weight gain, TV/video games, snacks while watching TV | OW: 10.5–11.0 h: ORadj = 0.77 (0.59 – 0.99) ≥11 h: 0.54 (0.40–0.73) OB: 10.5–11.0 h: ORadj = 0.53 (0.35 –0.80) ≥11 h: 0.45 (0.28–0.75) |
| Gupta et al, 2002 USA | 11–16 y old (N = 383) | Actigraphy (1 night) Referent: sleep duration as continuous | Measured height and weight; BMI >85th percentile (CDC) | — | For every additional h of sleep time, odds of OB decreased by 80%: OR = 0.20 (95th CI = 0.11) |
| Hui et al, 2003 China | 6–7 y old (N = 343) | Caretaker-reported Referent: <9 h | Measured height and weight; BMI ≥92nd centile, using Hong Kong cross-sectional growth survey as reference | Paternal and maternal obesity | OW: 9 –11 h: ORadj = 0.54 (0.30–0.97) ≥11 h = 0.31 (0.11–0.87) |
| Padez et al, 2005 d Portugal | 7.0–9.5 y (N = 4511) | Caretaker-report Referent: 8 h | Measured height and weight; age/sex BMI cut-off points by Cole et al | Sex and age | OW: 9–10 h: ORadj = 0.46 (0.40–0.51) ≥11 h: 0.44 (0.38–0.49) OB: 9–10 h: ORadj = 0.44 (0.40–0.47) ≥11 h: 0.39 (0.35–0.42) |
| Chen et al, 2006 Taiwan | 13 –18 y (N = 656) | Self-report of 6 –8 h of sleep (WD sleep) Referent ≥4 nights/wk | Measured height and weight; OW: BMI ≥85th percentile for age/sex (DOH) | — | OW: <4 nights/wk: OR = 1.74 (1.3–2.4) |
| Chaput et al, 2006 Canada | 5–10 y (N = 422) | Caretaker-report (WD sleep) Referent: 12 –13 h | Measured height and weight; OW/OB: age/sex BMI cut-off points by Cole et al | Age, sex, parental OB, parent education, income, single parent, breakfast, media use, sport activities, and whether breastfed | 10.5–11.5 h: ORadj = 1.42 (1.09 –1.98) 8 –10 h: 3.45 (2.61–4.67) |
| Eisenmann et al, 2006 c Australia | 7–15 y (N = 6324) | Self-report Referent ≥10 h | Measured height and weight; OW/OB: age/sex BMI cut-off points by Cole et al | Age | OW/OB: boys only: 9–10 h: ORadj = 1.61 (1.19–2.17) 8 –9 h: 1.83 (1.30–2.58) ≤8 h: 3.06 (2.11–4.46) |
| Seicean et al, 2007 USA | 15.6 ± 1.23 y (N = 509) | Self-reported (WD sleep) Referent >8 h | Self-reported height and weight (30% weighed themselves using a scale on scene); OW: age/sex ZBMI >85th percentile; OB>95th percentile (CDC) | Gender, age, irregular eating, health status, and caffeine intake | OW: <5 h: ORadj = 7.65 (1.87–31.30) 5–6: N/S 6–7 h: 2.55 (1.02–6.38) 7–8: N/S |
| Kuriyan et al, 2007 India | 6 –16 y (N = 598) | Caretaker-report (younger) or self-report (older) Referent >9.5 h | Measured height and weight; OW: age/sex BMI cut-off points by Cole et al | Age, gender, living location, and SES | OW: ≤8 h: ORadj = 6.7 (1.5–30.2) |
| Knutson et al, 2007 USA | 10 –19 y (N = 1546) | A) Self-report B) Self-report using time diaries Referents: A) 9.2–19.0 h B) 10.08–16.17 h | Measured height and weight; OW: BMI ≥95th percentile for age and gender (CDC) | Race, age, gender, family income, education, TV viewing, physical activity, and media use | OW: A) 7–8 h: ORadj = 1.85: (1.01–3.38) 8.1–9.0 h: 1.93 (1.10–3.37) B) All sleep categories NS. |
| Nixon et al, 2008 New Zealand | 7.3 y (N = 519) | Actigraphy (1 night) Referent ≥9 h | Measured height and weight; OW/OB: age/sex BMI cut-off points by Cole et al | Maternal BMI, maternal age, marital status, gender, h of TV, and sedentary activity | OW/OB: <9 h: ORadj = 3.32 (1.40–7.87) |
| Ievers-Landis et al, 2008 USA | 8 –11 y (N = 819) | A) Caretaker-report of sleep duration B) Child report using 7-d sleep diary Referent: duration as continuous | Measured height and weight (PC); OB: age/sex BMI ≥95th percentile (CDC) | Age, gender, preterm status, income psychosocial functioning, and parental stress | OB: A) ORadj = 1.41 (1.12–1.76) Odd of being OB increase by 41% with every 1 h of sleep decline B) ORadj = 1.45 (1.09–1.94) Odds of being OB increase by 45% with every 1 h of sleep decline |
| Liu et al, 2008 USA | 7 –17 y (N = 335) | Self-reported 7-d sleep diary Referent: duration as continuous | Measured height and weight; at risk: age/sex ZBMI 85th–95th percentile; OW ZBMI ≥95th percentile (CDC) | Age, sex, SES, ethnicity, puberty, and psychiatric diagnosis | OW: Reduced sleep (1 h less of): ORadj = 2.12 (1.05–4.28) |
| Wells et al, 2008 Brazil | 10 –12 y (N = 4452) | Self-report (WD sleep) Referent <9 h | Measured height & weight; IOTF guidelines used to define OW & OB | Sex, birth weight & length, maternal smoking and alcohol consumption during pregnancy, maternal pre-pregnancy BMI, SES, PA, systolic & diastolic BP, TV h | OB: ORadj = 9–10 N/S >10 h: N/S Odds of being OB decreased by 14% with every additional h of sleep |
| Bawazeer et al, 2009 Saudi Arabia | 10 –19 y (N = 5877) | Caretaker-report Referent >7 h | Measured height, weight, waist circumference & hip circumference; OB defined as >95th percentile BMI for age & gender | — | OB: boys ≤7 h: OR = 1.28 (1.09–1.50) girls ≤7 h: 1.38 (1.02–1.89) |
| Wing et al, 2009 China | 5–15 y (N = 5159) | Caretaker-report Referent >10 h | Parent report of height & weight converted to ZBMI (OW ZBMI between 85th and 95th percentile; OB ZBMI >95th percentile per CDC guidelines) | Age, gender, TV viewing, time to do homework, parent education, & eating 1 h before going to bed | OW/OB: Weekdays: ≤ 8h: ORadj = 1.74 (1.23–2.45) 8.01–9 h: 1.51 (1.13–2.03) 9.01–10 h: 1.30 (0.97–1.76) Weekends: ≤8 h: ORadj = 1.80 (1.05–3.09) 8.01–9 h: 1.66 (1.30–2.13) 9.01–10 h: 1.36 (1.12–1.66) |
| Hitze et al, 2009 Germany | 6–19 y (N = 414) | Caretaker-report (younger) and self-report (older) (WD sleep) Referent: Long sleep (9–10 h for younger; 8–9 h for older) | Measured height & weight; German references used to define OW & OB | Parent BMI, birth weight, change in weight birth-2 y, duration of breastfeeding | OB: girls only : Short sleep: ORadj = 5.5 (1.3–23.5) |
| Jiang et al, 2009 China | 3–4 y (N = 1311) | Caretaker-report Referent ≥11 h | Measured height & weight; Country norms used to define obesity (>95th percentile) | Age, sex, appetite, birth weight, maternal age at delivery, mother & father education, household income, & geographic location | OB: <9 h: ORadj = 4.76 (1.28–17.69) 9 h: 3.42 (1.12–10.46) 9.5 h = N/S 10.0 h = N/S 10.5 h = N/S |
| Ozturk et al, 2009 Turkey | 6–17 y (N = 5358) | Caretaker-report Referent ≥10 h | Measured height & weight; IOTF guidelines used to define OW & OB | — | OW/OB: boys only : ≤8h: OR = 2.06 (1.31–3.24) 8.1–8.9 h: 1.74 (1.10–2.75) 9.0–9.9 h: 1.86 (1.17–2.97) |
| Sun et al, 2009 b Japan | 12–13 y (N = 5753) | Self-report Referent 8–9 h | Measured height & weight; IOTF guidelines used to define OW & OB | Age, paternal overweight, maternal overweight, breakfast frequency, snacking frequency, nighttime snacking, eating speed, eating volume, physical activity, TV watching, video game playing | OW: girls only: <7h: ORadj = 1.81 (1.21–2.72) 7–8 h: 1.37 (1.00–1.88) ≥9 h = NS |
| Anderson & Whitaker, 2010 USA | ∼ 4 y (N = 8750) | Caretaker-report Referent <10.5 h | Measured height & weight; CDC guidelines used to define OB (≥95th percentile for age & gender) | Eating dinner as a family, screen viewing time, child age, gender, race/ethnic group, household income-to-poverty ratio, single-parent household, maternal education, maternal BMI, & maternal age | OB: <10.5 h: ORadj = 0.86 (0.71–1.03) |
| Longitudinal Studies | |||||
| Reilly et al, 2005 UK | 30 mo –7 y (N = 7758) | Caretaker-report (nocturnal sleep duration at 30 mo) Referent >12 h | Measured height and weight at 7 y; OB = BMI ≥95th centile using UK reference data | Maternal education, child’s sex, and energy intake at 3 y | OB: <10.5 h: ORadj = 1.45 (1.10–1.89) 10.5–10.9 h 1.35 (1.02 –1.79) 11–11.9h: N/S |
| Snell et al, 2007 USA | 3 –18 y (time 1: 3–12 y; time 2: 8–18 y; N = 1441) | Caretaker-report (younger) or self-report (older) | Measured height at all time points, caretaker-reported weight at T1; OW/OB: age/sex BMI cut-off points by Cole et al | Race, age, sex, BMI at T1, parent income, and parent education | Sleeping >11 h relative to 9.0–9.9 h associated with a 17.1% reduction in OW Every additional h at T1 decreased BMI at T2 by 0.75 kg/m |
| Lumeng et al, 2007 USA | 9 y to ∼12 y (N = 785) | Caretaker-report (24-h sleep) Referent: duration as a continuous variable | Measured height and weight; OW: BMI ≥95th percentile for age and gender (NCHS/CDC guidelines) | Gender, race, maternal education, ZBMI in third grade, and change in sleep duration | OW: Longitudinal : ORadj = 0.60 (0.36–0.99) For every additional h of sleep at 9 y child 40% less likely to be OW at 12 y Cross-sectional : ORadj = 0.80 (0.65–0.98) For every additional h of sleep in sixth grade, child ∼20% less likely to be OW |
| Landhuis et al, 2008 New Zealand | 5 –32 y (N = 780) | Caretaker-report (averaged over ages 5,7, 9, and 11 y) Referent: duration as a continuous variable | Measured height and weight at 32 y; BMI calculated | Sex, SES, parent BMI, TV, parental control, smoking as an adult, and adult PA | OB: ORadj = 0.65 (0.43–0.97) For every additional h of sleep in childhood, 35% less likely to be OB at 32 |
| Touchette et al, 2008 Canada | 2.5–6.0 y (N = 1138) | Caretaker-report (averaged over 2.5, 3.5, 4.0, 5.0, and 6.0 y) Referent: 11-h persistent sleep duration | BMI calculated at 2.5 & 6.0 y; IOTF guidelines used to define OW and OB. | Perinatal variables (eg, birth weight, parent education), child weight & nap duration at 2.5 y; lifestyle variables (eg, child overeating, snacking, snoring, TV, PA) | OW/OB: Short persistent sleepers (<10 h/night): ORadj = 2.9 (1.0–8.5) Short increasing & 10-h persistent = NS. |
| Taveras et al, 2008 USA | 6 mo–3 y (N = 915) | Caretaker-reported (24-h sleep averaged over the 6-mo, 1-y, and 2-y assessment) Referent ≥12 h/d | Measured height and weight; OW: age/sex BMI ≥95th percentile; (NCHS/CDC guidelines) | Maternal education, income, prepregnancy BMI, marital status, prenatal smoking, breastfeeding duration, child’s race/ethnicity, birth weight, 6-mo weight for length, average TV viewing, and daily active play | OW: ORadj = 2.04 (1.07–3.91) |
a OR (confidence interval) reflects comparison to sleep referent for that study.
b Represents studies sampled from the Toyama Birth Cohort.
c Biggs and Dollman (2007) supported these findings on the same dataset controlling for PA and diet.
d Padez et al (2009) presented similar findings on the sample controlling for parent education, parent obesity, PA, and TV watching.
As can be seen in Table 1 , for cross-sectional studies, the reference values for sleep length used to determine obesity risk varied from less than 7 hours of sleep per night to more than or equal to 12 hours per night. Despite these differences in how referents were defined, all studies demonstrated negative associations between sleep duration and obesity risk. It is important to note that most studies found significant results even after controlling for potential confounding variables (eg, parental BMI, birth weight, television viewing; see Table 1 for specific confounders controlled for in each study). However, it is also important to note that not every category of sleep was associated with increased risk for obesity. For example, Sekine and colleagues found that in comparison to children who slept 11 hours or more each night, there was no increased risk for obesity for children sleeping less than 9 hours or 10 to 11 hours per night, but that there was an increased risk for obesity for children sleeping 9 to 10 hours per night. Furthermore, when associations were examined separately in boys and girls, some studies found significant results for one gender but not the other.
In addition to those studies presented in Table 1 , 6 additional studies were conducted, but did not present findings in terms of odds ratios. All 6 studies found consistent results with less sleep being associated with an increased risk for obesity. However, one study only assessed this association in adolescent girls and a second study only found significant results in girls.
Six prospective studies were also identified (see Table 1 ). Findings are consistent with cross-sectional studies. For example, Snell and colleagues found that for every additional hour of sleep obtained at time 1 (when children were 3–12 years of age), caretaker-reported BMI decreased by 0.75 kg/m 2 at time 2 (when children were 8–18 years old). Similarly, Touchette and colleagues found that between 2.5 years and 6 years of age, children who consistently obtained short sleep were 2.9 times more likely to be overweight or obese than children who consistently slept 11 hours or more each night even after controlling for potential confounding factors. Consistent with these findings, but over a much longer follow-up, Landhuis and colleagues found that for every additional hour of sleep obtained during childhood (averaged across 5–11 years), individuals had a 35% reduced risk of obesity at 32 years of age.
Sleep Duration and Other Anthropometric Indices
In addition to risk for overweight and obesity, more recent studies assessed the association between sleep duration and other indices of body composition. A total of 11 studies were identified, 3 of which used 2 or more measures to assess body fat. Five studies used skinfold thickness, 4 used waist circumference, and 3 used bioelectrical impedance analysis (BIA). Two additional studies used another measure, such as dual x-ray absorptiometry and air displacement plethysmography. Regardless of measure, however, an increase in sleep duration was consistently found to be associated with lower body fat.
For example, Nixon and colleagues found that compared with 7-year-old children sleeping 9 hours or more per night (as measured by actigraphy), children sleeping less than 9 hours per night had an increase of 3.34% body fat (as measured by BIA). Similarly, von Kries and colleagues found that when compared with children aged 5 to 6 years sleeping less than 10 hours per night, children sleeping 11.5 hours or more per night had a decreased risk for high body fat (defined as excessive fat mass > the 90th percentile for age and gender using BIA).
It should be noted that 3 studies found that significant findings varied across gender. In a sample of twins aged 10 to 20 years, Yu and colleagues found that shortened sleep length (<8 hours per night) was negatively associated with total body fat and truncal fat, and positively associated with percent lean body mass as measured by DEXA in girls only. Similarly, although Hitze and colleagues found that short sleep was associated with increased fat free mass in both genders (using air displacement plethysmography), they only found differences in percent body fat in girls.
Findings regarding waist circumference and nocturnal sleep length were less consistent than those previously mentioned. For example, although Hitze and colleagues found significant findings across genders in linear analyses, when comparing short versus long sleepers, only short-sleeping girls had significantly larger waist circumferences. Yu and colleagues also found a significant association between sleep duration and waist circumference in girls only. In contrast, Eisenmann and colleagues found that greater sleep duration was associated with decreased waist circumference in boys aged 7 to 16 years, but no consistent relationship was found in girls.
Additional Sleep Indices and Obesity Risk
In addition to the assessment of sleep duration, several studies assessed other sleep measures to determine whether additional sleep parameters may be associated with obesity risk. The primary variable of interest was the timing of sleep (ie, bedtime and rise time), which was typically assessed with a single-item question (eg, “over the past week, what was your typical bedtime?”). Together, these studies suggest that later bedtimes are associated with increased risk for obesity. However, no association between rise time and obesity risk was found in these studies. Of note, one study with preschool-aged children (3 years) found that early rise time (ie, ≤7:00 am ) was associated with an increased obesity risk, but that later bedtime was not.
In addition to bedtime and rise time, 3 additional studies assessed the association between irregular or problematic sleep and obesity risk. In the first study, parent report of irregular sleep habits at 2 to 4 years of age was independently associated with obesity risk in young adulthood (ie, at 21 years of age). Furthermore, Wing and colleagues attempted to assess how catching up on sleep on weekends and holidays may influence children’s risk for obesity. The findings suggested that compared with children who slept greater than 10 hours per night, children who persistently slept 8 hours or less on weekdays and weekends or on weekdays and during holidays, were at the greatest risk for obesity (odds ratio adjusted for confounders [OR adj] = 2.59 [1.22–5.48] and 2.32 [1.00–5.53], respectively). In contrast to findings from these studies, after adjusting for potential confounding variables, no association was found between parent-reported sleep problems (using a modified version of the Children’s Sleep Habits Questionnaire) in the third or sixth grades and obesity risk in the sixth grade.
Finally, 2 studies assessed the association between stages of sleep and obesity risk. In the first study (which is also presented in part in see Table 1 ), Liu and colleagues found that reduced rapid eye movement (REM) sleep and reduced REM density were each associated with increased obesity risk in children aged 7 to 17 years. In a second study of 52 adolescents aged 12 to 18 years who presented to a sleep clinic, greater stage 1 sleep was found for adolescents who were obese compared with those who were normal weight, and greater slow wave sleep was also found in adolescents who were categorized as overweight compared with those who were obese.
Potential Mediators of the Sleep-Weight Association
Several studies have moved beyond documenting sleep-weight associations to examining variables (eg, eating) that may mediate the relationship between sleep and obesity risk. For example, Landis and colleagues found that food cravings were higher in those with more daytime/less nocturnal sleep. Touchette and colleagues found that parent report of child overeating (at 6 years of age) might play a small role in the association between short sleep and BMI. When removed from the statistical model to predict BMI, there was a small increase in the odds for children classified as short persistent sleepers to be obese (see Table 1 ). Finally, Westerlund and colleagues found that shorter sleep was associated with greater consumption of energy-dense foods, such as pizza, pasta, and refined sugars. This relationship was stronger in boys and on weekdays. Additional gender differences included greater problems with waking in the morning being associated with increased intake of energy-dense foods in boys, and longer weekday sleep duration being associated with greater consumption of nutrient-dense foods (ie, fruits and vegetables) in girls.
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