Is sleep deprivation a contributor to obesity in children?

Review

DOI: 10.1007/s40519-015-0233-9

Cite this article as:
Chaput, JP. Eat Weight Disord (2016) 21: 5. doi:10.1007/s40519-015-0233-9
Part of the following topical collections:
  1. Sleep and Obesity

Abstract

Chronic lack of sleep (called “sleep deprivation”) is common in modern societies with 24/7 availability of commodities. Accumulating evidence supports the role of reduced sleep as contributing to the current obesity epidemic in children and youth. Longitudinal studies have consistently shown that short sleep duration is associated with weight gain and the development of obesity. Recent experimental studies have reported that sleep restriction leads to weight gain in humans. Increased food intake appears to be the main mechanism by which insufficient sleep results in weight gain. Voluntary sleep restriction has been shown to increase snacking, the number of meals eaten per day, and the preference for energy-dense foods. Although the causes of sleep loss in the pediatric population are numerous, more research looking at screen exposure before bedtime and its effects on sleep is needed given the pervasiveness of electronic media devices in today’s environment. Health professionals should routinely ask questions about sleep and promote a good night’s sleep because insufficient sleep impacts activity and eating behaviors. Future research should examine the clinical benefits of increasing sleep duration on eating behaviors and body weight control and determine the importance of adequate sleep to improve the treatment of obesity.

Keywords

Sleep loss Adiposity Appetite Eating behavior Energy balance Exercise 

Introduction

Sleep curtailment as a possible cause of obesity has received considerable attention in the media and scientific literature over the past decade. Interest in this topic area has been partly fueled by the apparent paradox that sleep—the most sedentary activity of all—could be associated with leanness [1]. Additionally, research has shown that declines in sleep duration occurred concurrently with increases in obesity prevalence in children and adolescents [2, 3], leading scientists to believe that lack of sleep could be partly responsible for the obesity epidemic [4]. The modern way of living, with its 24/7 lifestyle, appears to be an important driver of this “sleep deprivation epidemic” [5]. Many people consider “sleep” as a waste of time and few people really understand the adverse effects of reduced sleep time on overall health [5].

Factors responsible for the secular decline in sleep duration in the pediatric population are not well understood. However, declines in children’s sleep duration have occurred as a result of progressive delays in bedtimes, but unchanged wake time [6, 7, 8]. Delays in children’s bedtimes have been attributed to activities that keep children awake and contexts that allow them to do so such as technology use, schoolwork, and part-time employment [9, 10, 11]. Similarly, artificial light, caffeine use, and parental attitudes have been identified as contexts that allow children to have later bedtimes [12, 13, 14].

The term “lack of sleep” generally refers to an insufficient amount of sleep for optimal functioning. While the ideal amount of sleep per night varies from one person to another, the National Sleep Foundation recommends between 10 and 13 h for preschoolers, 9–11 h for school-aged children, and 8–10 h for adolescents to maximize overall health and well-being [15]. Although the vast majority of studies assess “sleep duration” as it relates to health outcomes, an assessment of optimal sleep reaches well beyond the notion of sleep quantity, including sleep quality, timing, architecture, consistency, and continuity.

The objective of this narrative review is to provide an overview of sleep deprivation as a possible contributor to obesity in children and youth. The most plausible mechanisms by which a lack of sleep may lead to weight gain are discussed. The present contribution goes well beyond a synthesis of available studies in the field and possible mechanisms; the adverse influence of electronic screen devices on sleep hygiene is discussed and tips for health professionals to assess sleep are given.

Sleep deprivation as a contributor to obesity in children: observational evidence

An accumulating body of epidemiologic evidence associates short sleep duration with obesity and weight gain in children. For example, Cappuccio et al. [16] conducted a meta-analysis including 30,002 children from around the globe and found a pooled odds ratio (OR) of 1.89 [95 % confidence interval (CI) 1.43–1.68] for short sleep duration and its association with obesity. Likewise, Chen et al. [17] reported that children with shorter sleep duration had a pooled OR of 1.58 (95 % CI 1.26–1.98) for overweight and obesity, and children with shortest sleep duration had an even higher risk (OR 1.92; 95 % CI 1.15–3.20) when compared to children having longer sleep duration. Overall, these two meta-analyses published in 2008 concluded that cross-sectional studies from around the world show a consistent increased risk of obesity among short sleepers in children.

More recently, Fatima et al. [18] explored the longitudinal associations between short sleep and overweight/obesity in children and adolescents using a systematic approach and bias-adjusted meta-analysis. The systematic review included 22 longitudinal studies, with participants from diverse backgrounds, and showed an inverse association between sleep duration and body mass index. Their meta-analysis included 11 longitudinal studies, comprising 24,821 participants, and revealed that subjects sleeping for short duration had twice the risk of being overweight/obese compared to those sleeping for long duration (OR 2.15; 95 % CI 1.64–2.81). These findings are in line with those published by Magee and Hale [19] in their systematic review published in 2012 showing that shorter sleep duration consistently predicts subsequent weight gain in children.

Causal inference in epidemiologic studies is difficult due to the lack of control for important confounders (e.g., depression, psychosocial problems, chronic illness, medications) and inconsistent evidence of temporal sequence in prospective studies. Moreover, there may be bidirectional effects (insufficient sleep causing weight gain and vice versa), thereby creating a setting for a vicious circle [20]. Another concern is the reliance on self-reported sleep in most observational studies, which is subject to bias and can impact associations with adiposity [21]. However, despite common limitations associated with observational studies, there is a preponderance of evidence to suggest that sleep deprivation is a contributor to weight gain in children and youth [22]. Future longitudinal studies should (i) use an objective assessment of sleep (e.g., actigraphy), (ii) measure sleep and adiposity at multiple time points over time, (iii) include and investigate more carefully confounding, mediating and moderating variables, and (iv) examine the relationship between sleep and adiposity across countries representing a wide range of socio-cultural and socio-economic variability (most studies to date have been conducted in high-income, developed countries).

Sleep deprivation as a contributor to obesity in children: experimental evidence

A growing body of experimental evidence shows that sleep restriction is a stressor and exerts wide-ranging adverse effects on a variety of body systems [23]. The seminal study by Spiegel et al. [24] published in 2004 was a starting point in the elaboration of short-term experiments aimed at examining the effects of sleep restriction on energy balance. In their study, adults subjected to 4 h in bed exhibited increased levels of ghrelin (an orexigenic hormone) and decreased levels of leptin (an anorexigenic hormone) and reported increased sensations of hunger and appetite. More recently, intervention studies have provided important information to the effect that the hormonal explanation is probably not the most important mechanism to explain the link between reduced sleep and increased food intake [25]. Differences in methodology (e.g., sleep timing) and the nutritional state and energy balance of study participants can also contribute to explain the conflicting results with regard to ghrelin and leptin concentrations.

Recent experimental studies have been able to demonstrate that sleep restriction leads to weight gain in humans. Spaeth et al. [26] examined the effect of experimental sleep restriction (5 consecutive nights of 4 h in bed per night) on weight gain in 225 healthy adults and showed that sleep-restricted participants gained 1 kg more than control participants. The weight gain resulting from sleep restriction was due to an increase in meal consumption frequency and the ingestion of about 550 additional calories between 22:00 and 03:59. These results agree with those of Markwald et al. [27] showing that 5 days of 5 h of sleep per night resulted in a 0.82 kg weight gain in healthy adults. Increased food intake was also the main explanation of these findings and the authors observed that transitioning from an insufficient to adequate/recovery sleep schedule decreased energy intake and led to weight loss. Experimental studies in the pediatric population are scarce but recent results from Hart et al. [28] showed that compared with decreased sleep, increased sleep duration in school-aged children resulted in lower food intake and lower weight. These new findings provide compelling evidence for further understanding how intervening on sleep duration could impact children’s weight status.

Although experimental studies are useful in showing a possible causal link between sleep curtailment and weight gain, the tightly controlled laboratory setting limits external validity of findings. Another limitation of intervention studies in this field of investigation is that they are of short duration, lasting only a few days. It is thus unknown if the observed acute effects can persist on a chronic basis. Long-term randomized controlled trials of sleep restriction on the development of obesity would not be possible for logistic and ethical reasons; therefore, we need to rely on the available evidence and, all together, it is reasonable to say that sleep deprivation plays a role in the risk of developing obesity. From a public health perspective, there is minimal risk in taking a pragmatic approach and recommending healthy sleep habits as an adjunct to other health promotion measures [29, 30, 31].

Mechanisms by which sleep deprivation may lead to weight gain

To induce weight gain, reduced sleep must either increase food intake and/or reduce energy expenditure. The mechanisms by which a lack of sleep can lead to weight gain and obesity are illustrated in Fig. 1. According to the best available evidence in the field, the main explanation is through an increase in food intake [32]. In fact, experimental sleep restriction has even been shown to increase 24-h energy expenditure by ~5 % due to the energy cost of additional wakefulness [27, 33]. A decrease in physical activity energy expenditure is nevertheless possible for some individuals, especially due to fatigue and tiredness resulting from sleep deprivation. However, large inter-individual variations have been reported and we concluded from a comprehensive review of the evidence that short sleep duration does not substantially affect components of energy expenditure [34]. Conversely, there is robust evidence showing that reduced sleep increases food intake [35, 36, 37], highlighting that “energy in” is a key mediator of the association between sleep deprivation and weight gain/obesity.
Fig. 1

Most plausible mechanisms by which sleep deprivation may lead to weight gain and obesity. Adapted from Chaput [5]. The symbol (?) means a lack of scientific support

It is well documented that sleep deprivation enhances our vulnerability to overeat in the current obesogenic environment [32, 35, 36, 37]. There is growing and consistent evidence demonstrating that short sleep duration, poor sleep quality and later bedtimes are all associated with increased food intake, poor diet quality, and excess body weight [32]. As discussed earlier, excess energy intake associated with sleep curtailment appears to be preferentially driven by hedonic rather than hormonal factors [25, 32]. Although food intake may be directly proportional to the time spent awake in the current obesogenic environment, studies consistently show that reduced sleep increases snacking, the number of meals consumed per day, and the preference for energy-dense foods [32]. There is also evidence to suggest that adolescents’ diet after sleep restriction is characterized by higher glycemic index and glycemic load, particularly desserts and sweets [38]. Whether this behavior is linked to the body trying to increase readily available glucose for cognitive functions remains to be demonstrated. New neuroimaging experiments have provided evidence that sleep restriction enhances hedonic stimulus processing in the brain underlying the drive to consume foods [39, 40, 41]. In particular, the insular cortex and areas thought to be involved in hedonic functions (e.g., orbitofrontal cortex and dorsolateral prefrontal cortex) have been found to display the strongest activation in response to unhealthy food compared to healthy food stimuli after sleep restriction [41].

From an evolutionary perspective, animals that stayed awake would need rapid fuel (glucose) for the brain and nervous system either for predating or avoiding predators, suggesting that increased energy intake (especially energy-dense foods) can be seen as a normal physiological adaptation to provide energy needed to sustain wakefulness. Future studies should focus more on understanding the rewarding aspects of food that accompany sleep restriction [42]. Furthermore, strategies should be proposed to individuals more likely to overeat under sleep restriction to prevent weight gain.

Lack of sleep in the modern world: influence of screens on sleep hygiene

The presence of electronic screen devices in a child’s bedroom has gained in popularity, and children report using these technologies late at night [43, 44, 45]. For example, 71 % of American (US) children and youth report having a television in their bedroom [44]. An accumulating number of studies have found associations between screen time in children’s bedroom and poor sleeping habits [46, 47, 48]. It is thus not surprising that the American Academy of Pediatrics recommends that parents remove TV sets and internet-connected electronic devices from children’s bedrooms [49].

It is increasingly recognized that screen exposure may increase sleep disturbances [50]. Electronic media use may increase physiological and mental arousal, making it more difficult to fall asleep [51]. Computer use and TV viewing may also affect sleep architecture by decreasing slow-wave sleep, REM sleep and sleep efficiency [51, 52], and the bright light of screens has been reported to suppress melatonin secretion, which may delay sleep onset [53, 54]. It has been shown that a 2-h exposure to self-luminous tablets before bed results in a suppression of melatonin [55]. In humans, exposure to short-wavelength monochromatic light in the evening induces greater circadian and alerting responses than exposure to the same number of photons of longer wavelength monochromatic light, even though the shorter wavelength light may have a much lower illuminance level when measured in lux [56]. Aside from the effects of the light emitted from electronic media devices, the content of the media (e.g., violence) may also stimulate a stress response through various emotions [57].

Today’s youth have the possibility to be connected at any location, 24 h a day, which has clear implications for sleep hygiene. Many adolescents are using technology within the hour before trying to fall asleep or using cell phones in bed, which interferes with the ability to fall asleep and stay asleep throughout the night [58]. Many adolescents are addicted to their cell phone and answer text messages during the night and/or answer calls [58]. It is thus timely to fully document the adverse effects of screen exposure before bedtime (and find solutions) in a context where screens are omnipresent in the daily schedule of individuals.

Recent evidence is also showing bidirectional relationships between insufficient sleep and screen time in children, suggesting that lack of sleep and media use could be interacting problems, particularly for children from lower socio-economic households [59]. These are important issues to consider since both inadequate sleep and screen time predict adverse health outcomes in children [60, 61]. Future research should try to understand how best to support parents and caregivers in implementing and sustaining good sleep hygiene and TV-free bedrooms for their children. Recent results from a randomized trial are promising and show that promoting household routines, particularly increasing sleep duration and reducing TV viewing, may be an effective approach to reduce BMI among low-income, racial/ethnic minority children [62]. Additionally, manufacturers should design self-luminous display screens that can decrease circadian stimulation, especially for the hours before bed, to facilitate a good night’s sleep.

Why health professionals should ask questions about sleep?

Few health professionals have the opportunity to learn about the process of sleep and its impact on health. The recent demonstration that sleep deprivation is a contributor to weight gain and obesity has emphasized the need to include sleep hygiene in health assessments and lifestyle modification interventions [63]. It is prudent for health professionals to ask questions about sleep and promote a good night’s sleep given the influence of insufficient sleep on activity and eating behaviors. Sleep deprivation increases the desire to eat and can impact physical activity level, thereby rendering adherence and compliance to behavior changes more difficult for patients.

Assessing general sleep hygiene (sleep duration, quality, timing) does not need to be long and complicated and can efficiently be incorporated into any health and lifestyle assessment. Table 1 provides a sample of questions that can be included in screening, assessment, and/or monitoring sessions. Health professionals should also ask questions about the causes of a possible inadequate sleep pattern. The reasons can be very different between individuals and parents should be included in this assessment. Rules about bedtime in the household and making sure that gadgets are out of the child’s bedroom are important in the promotion of healthy sleep hygiene. Additionally, health professionals should determine when referral to a sleep specialist is needed. Patients describing symptoms that align with a sleep disorder (e.g., obstructive sleep apnea) should be referred to a sleep specialist. Table 2 provides an overview of recommendations for improving sleep.
Table 1

Examples of sleep questions that can be included in the assessment

Sample questions

Desired answers

1. What time do you go to bed every night and wake up every morning?

Consistent (even on weekends)

2. How many hours do you sleep on an average night?

10–13 h (preschoolers), 9–11 h (school-aged children), 8–10 h (adolescents)

3. Do you have difficulty falling asleep once in bed?

No, usually I fall asleep within 30 min

4. How many times do you wake up each night?

Never or once per night

5. Do you feel refreshed upon waking in the morning?

Yes

6. How often do you feel sleepy during the day?

Never or rarely

Adapted from Golem et al. [63]

Table 2

General tips for having healthy sleep hygiene

Go to bed and wake up at the same time every day (even on the weekends!)

Avoid caffeine consumption (e.g., coffee, soft drinks, chocolate) starting in the late afternoon

Avoid drinking alcohol in the evening

Avoid smoking cigarettes

Expose yourself to bright light in the morning—sunlight helps the biological clock to reset itself each day

Make sure your bedroom is conducive to sleep—it should be dark, quiet, comfortable, and cool

Sleep on a comfortable mattress and pillow

Exercise regularly during the day

Develop a relaxing routine before bedtime—ideas include bathing, music, and reading

Do not go to bed feeling hungry, but also do not eat a heavy meal right before bed

Do not have pets in your bedroom

Reserve your bedroom for sleeping only—keep cell phones, computers, televisions and video games out of your bedroom

Conclusions

Sleep deprivation is pervasive in modern societies, and there is robust evidence supporting the role of reduced sleep as contributing to the current obesity epidemic in children and youth. Increased food intake seems to be the main explanation as to why a lack of sleep can lead to weight gain. Future research should aim to examine the clinical benefits of increasing sleep duration on eating behaviors and body weight control [64, 65]. Additionally, we need to better understand the importance of adequate sleep to improve the treatment of obesity [66]. Given that behavioral sleep restriction appears to be linked to our modern way of living, short sleepers may find it difficult to maintain a healthy lifestyle in the current environment that promotes overconsumption of food and sedentary behaviors. Sleep is not a “waste of time”, and public health efforts should aim to better promote a good night’s sleep for overall health.

Acknowledgments

Jean-Philippe Chaput holds a Junior Research Chair in Healthy Active Living and Obesity Research.

Compliance with ethical standards

Conflict of interest

The author declares that he has no conflict of interest.

Ethical approval

This article does not contain any studies with human participants performed by any of the authors.

Informed consent

For this type of study formal consent is not required.

Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  1. 1.Healthy Active Living and Obesity Research GroupChildren’s Hospital of Eastern Ontario Research InstituteOttawaCanada

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