Sleep deficiency in young children

Introduction

As early as the prenatal period, sleep is vital to the health and development of all children. Amid the epidemic of insufficient sleep in adulthood, there is growing public health concern in response to the evidence that 25-40% of children are reported to have sleep insufficiency before they are school-age,^1-3 placing them at risk for sleep-associated poor health outcomes, including metabolic,⁴ cardiovascular, ⁵ and mental health.⁶ In addition, when sleep problems develop in early life, they often are persistent,^{3, 7} contributing to long-term problems with school performance, quality of life, risk of injury, and mental health.^8-13 Adding to the public health concern is the increasing evidence that minoritized children have higher levels of sleep deficiency^14-17 and are at increased risk of associated health disparities ^{18,19, 20} compared to non-Hispanic White children. Moreover, there is emerging evidence that sleep health disparities emerge as early as 1 year of age.^{16, 21, 22} The purpose of this review is to summarize the key advances in our understanding of sleep health in early childhood (i.e. birth through school age) and the possible role of sleep deficiency during early childhood in the development of health disparities.

Sleep and health in children

Recently there has been a sharp growth in the research attention given to childhood sleep patterns, development, and disorders.²³ Notably, the official statement on the importance of healthy sleep by the American Thoracic Society included recommendations to increase our understanding of how sleep health and sleep disorders develop from early life and across the lifespan as a priority in future research.²⁴ Moreover, the statement highlighted that the physiological and clinical basis for approaches to sleep health need to be tailored differently when considering pediatric sleep.

Historically, research on sleep and sleep-related disorders has focused on sleep as an outcome, rather than a predictor of health.¹⁹ As such, sleep health promotion messaging has been largely absent in public health messaging.²⁵ The shift in research to examining sleep as a predictor of health has prompted the characterization of sleep health as a multidimensional construct that includes sleep duration, efficiency, satisfaction, alertness/sleepiness, and timing.²⁵ This was recently re-evaluated as it applies to childhood; importantly, an additional dimension, sleep-related behaviors, was added to the child-specific definition in order to capture bedtime routines and the consistency of sleep timing and duration that may influence child sleep.²⁶

Sleep-related behaviors include the actions and activities that may promote or inhibit sleep health in children prior to bedtime and the regularity of those actions and activities. The establishment of a consistent routine that occurs in the hour preceding bedtime has been associated with earlier bedtimes, shorter sleep onset latency, fewer night awakenings, and longer sleep duration.²⁷ The addition of sleep-related behaviors to the pediatric-specific definition of sleep health brings important awareness of the influence of parental control on the sleep health of young children.²⁶ This relationship is highlighted in Sadeh’s transactional model of infant sleep that highlights parenting as the most proximal influence on children’s sleep in the early years.^{28, 29} The model describes how the relationship between parenting and early childhood sleep is influenced by parent’s beliefs, expectations, and behaviors related to their child’s sleep.

Regarding the other five dimensions of sleep, sleep duration has been the most extensively studied in connection with adverse outcomes. Sleep duration refers to the total duration of sleep within a 24-hour period. Shorter night sleep duration in children has been associated with lower levels of social interaction, cooperation, and peer acceptance,^{6, 30, 31} increased likelihood of aggressive behavior, anxiety,³² and depression. In children between 29 and 72 months of age, children with persistent short sleep duration showed a heightened risk for a low vocabulary receptive score in comparison with children with greater than 10 hours of sleep.³³ Studies have shown a link between adiposity and sleep health, primarily a negative correlation between sleep duration and adiposity, with shorter sleep duration predicting both concurrent and future increased adiposity.^34-36 Shorter sleep duration was also associated with greater time spent using the computer or television, which may also contribute to adiposity. ³⁷ Increased total sleep duration was associated with better emotional response regulation ^{38, 39}, and greater capacity for receptive vocabulary. ^{6, 40} However, shorter sleep duration has not consistently been shown to result in anxiety and depression across all studies, ⁴¹, and a prospective study found that nighttime sleep duration at 30 months was not predictive of receptive vocabulary when measuring subjects at 60 months,⁴² warranting a need for further studies and reporting of potential confounding factors. Interestingly, it is important to consider that there can be a discrepancy between parental and teacher perspectives on the association between sleep duration and attention; parents reported a positive association between sleep duration and attention, while teachers did not.⁴³ These results highlight an important angle for continued study, and touch upon the importance of involving both parents and teachers in the child’s sleep and related outcomes.

Apart from sleep duration, sleep efficiency is perhaps the next most studied sleep health dimension with respect to overall health outcomes. Children’s ability to fall asleep and stay asleep during the night is a major contributor to their sleep efficiency. Numerous health outcomes are associated with sleep efficiency, including conduct problems, anxiety, depression, and cognitive abilities, including memory and recognition. ⁴⁴ For example, conduct problems have been associated with a longer sleep onset latency and greater nighttime wakefulness in 57- and 68-month-old children.^{30, 45} Mixed or non-significant results were shown when examining bedtime, sleep efficiency, sleep onset latency, or total sleep duration and pro-social behavior. ^{6, 30, 31} Greater duration of nighttime wakefulness was associated with anxiety and depression.³² In a separate study, sleep problems were also associated with literacy and numeracy abilities, but no relationship with receptive vocabulary was found.⁴⁶

While recommendations for pediatric sleep duration exist,⁴⁷ age- and sex-based recommendations for other dimensions of sleep health such as alertness and sleep satisfaction are still lacking. These dimensions have received less research attention in pediatrics than the other dimensions of sleep health such as duration and efficiency. Sleep satisfaction is characterized by the subjective perception of sleep as ‘good’ or ‘poor’. As such, measurement of sleep satisfaction and alertness in young children are dependent on parent-report. Parental reports of children’s sleep satisfaction commonly differ from objective measurement of children’s sleep⁴⁸ and are influenced by parents’ mental health and their own sleep health.⁴⁹ Furthermore, sleep satisfaction is the most difficult dimension of sleep health to measure in children, adolescents, and adults^{25, 26} and few validated measures of pediatric sleep satisfaction/quality are available.^{26, 50} There is emerging evidence that sleep satisfaction/quality over a 7-day period significantly predicted psychological stress and general health among 5-9 year old children.⁵¹

Important maturational changes to the circadian and sleep homeostatic processes during childhood are critical to the assessment of children’s alertness/sleepiness. Perhaps most notably, early childhood is marked by a higher homeostatic sleep pressure that underlies children’s need for naps.⁵² Napping decreases with age as the homeostatic sleep process decreases throughout childhood.⁵² However, there is evidence that racial and ethnic differences exist in napping among 2-8 year old children and this finding warrants further investigation.⁵³ Children’s alertness or sleepiness during the daytime also has implications for many dimensions of their life, from education to health and development. Recent evidence suggests that sleepiness in childhood is related to some, but not all, cognitive and academic performances. Specifically, the effects of sleepiness were more profound on verbal than non-verbal abilities and on higher cognitive functions such as executive function and divergent thinking than on more automatic, less complex cognitive functioning.⁵⁴ More research in this area is needed to understand the relationship between sleepiness and learning in childhood.

In summary, clear associations have been established between sleep duration and behavioral, cognitive, and mental and physical health outcomes. However, according to a recent systematic review, there remains a paucity of research on the other sleep domains and varied health outcomes.¹⁹ Moving forward, research on pediatric sleep outcomes should work towards examining sleep as a multi-dimensional construct including sleep-related behaviors. Additionally, high-quality research on the biological need for sleep, and barriers and facilitators of good sleep health is also needed.²⁴

Sleep health inequities in early childhood

There are critical socioecological factors that are now recognized as relevant to the study of sleep health. Placing sleep health within a social-environmental conceptual framework may clarify the relationship between sleep and race, ethnicity, racism, and socioeconomic disadvantage.⁵⁵ Following the evidence of race and ethnicity differences in adult sleep, studies have emerged describing similar differences in children’s sleep patterns. More research is needed to examine the role of the personal, interpersonal, community, and societal influences on sleep health in early childhood (see Figure 1).⁵⁶ The complexity of elucidating the mechanism behind ethnic and racial sleep differences in sleep health includes such factors as the physical home (e.g., crowded homes, availability of sleep space), community (e.g., noise, violence, light pollution), and society (e.g., parent work schedules and reliance on public transportation to childcare that may require additional commute time and earlier awakening).⁵⁷ These factors are different across the developmental stages of childhood. For example, among older children, environmental conditions (e.g., noise, temperature) and pre-sleep worries (e.g., about family, friends) explained 29% of the association between socioeconomic status (SES) and sleep/wake problems.⁵⁸ Ultimately, it is vital that clinicians consider the complex interplay between sleep health dimensions and environmental exposures when assessing children’s sleep.

Figure 1.

Social ecological influences of sleep health in childhood.

Multiple studies on sleep in early childhood have found non-Hispanic White children’s nighttime sleep duration is on average 20 to 88 minutes longer than Hispanic and Black children.^{53, 59, 60} Non-Hispanic White children are also 1.4 to 1.8 times more likely to have a bedtime routine compared to Hispanic and Black children.^{61, 62} While there is compelling evidence that race and ethnic disparities exist in obtaining recommended sleep duration and timing, the mechanisms are less understood.⁵⁷ A recent systematic review of racial disparities in early childhood sleep suggested that cultural attitudes, acceptability of bedtimes, regular naps, and sleep practices are among the most common mechanisms supported in the literature.⁵⁷ While many of these mechanisms are likely modifiable with tailored sleep education and intervention programs, more research is needed to develop and test such approaches in early childhood.

There is limited research on sleep characteristics among young children living with socioeconomic adversity. However, shorter sleep duration and disrupted sleep patterns are more prevalent among socioeconomically disadvantaged children,⁶³ rendering these children more vulnerable to adverse health problems.^{21, 64-66} The majority of existing research has focused on adolescents and adults with higher SES. However, there is emerging evidence that decreased sleep duration and sleep efficiency occurs as early as one year of age among children living with socioeconomic adversity.^{21, 63, 64}

Sleep health and adverse childhood experiences

While it is well known that sleep deficiency contributes to many health problems, less is known about how adversity contributes to sleep deficiency and how sleep deficiency, in turn, contributes to the activation of children’s stress response systems.⁶⁷ Over the past decade, advances in the fields of neuroscience, molecular biology, genomics, developmental psychology, epidemiology and sociology have supported a paradigm shift in understanding the root of many poor health outcomes in adulthood. As such, disorders exhibited in adulthood can be traced back to adverse experiences early in life that resulted in a prolonged stress response, termed toxic stress, with negative health consequences across the lifespan.⁶⁸ Again, more prospective research is needed with inclusive sampling of young children to understand how adverse childhood experiences and sleep health in early childhood influence sleep problems in adulthood, but the evidence from retrospective adult studies is strong. According to a systematic review, the majority of these studies have documented statistically significant associations between sleep problems in adulthood and adverse early childhood experiences, as well as a dose-response relationship wherein the higher the number and severity of the adverse experiences reported by adults during their childhood, the stronger the association with their current sleep problems.⁶⁹ Furthermore, there is strong evidence that adults’ sleep health is associated with objectively measured physiologic biomarkers within the stress response system.^{5, 70-72} Thus, prospective examination of the associations between children’s sleep, stress response, and health may help understand how sleep deficiency in early childhood may contribute to the biological embedding of adverse childhood experiences or,conversely, may buffer the risk of developing toxic stress.⁷³ There are a growing number of studies currently underway to advance the science in this area.^{67, 74}

Approaches to improve sleep of children

Interventions aimed at promoting healthy sleep duration and efficiency early in life may be important to reducing the sleep disparities among very young children living with adversity and preventing some of the negative short- and long-term sequelae. While the research on young children’s sleep and their health lags behind the studies of adolescents and adults, there is a consensus that healthcare providers should be trained in the importance of sleep health and how to effectively promote sleep health with their patients.²⁴ There are considerable differences between child and adult sleep that are important to understand before sleep training recommendations are presented to parents. To begin with, sleep in the first 3 months of life characterized by equal time in NREM and REM sleep.⁷⁵ The lack of sleep cycles before age 3 months is the reason why sleep training is not effective and therefore not recommended before this age. As infants progress through the first year of life, they begin to develop three stages of NREM sleep and REM sleep continues to be longer than that of adults. Daytime napping is also important for infant sleep, but this need decreases with age. In particular, a drastic reduction in napping duration occurs between 18 months and 4 years of age.⁷⁶ It is not until the age of 4-5 years that children’s sleep architecture resembles that of adults.⁷⁷ However, as with adult sleep patterns, it is important to acknowledge that the specific patterns are individually variable.

Interventions to promote healthy sleep habits, including parent education,⁷⁸ positive bedtime routines (e.g., reading, bathing),^{79, 80} and extinction techniques to address bedtime resistance and nocturnal awakenings ⁸¹ are efficacious from late infancy into the preschool years.^{81, 82} Studies on behavioral sleep interventions (BSIs) in early childhood have demonstrated modest effects on the improvement of sleep duration and sleep quality with parent-reported sleep measures.^83-87 However, few studies included racially and ethnically diverse families who live with socioeconomic adversity and in socioecological contexts described above that may limit the feasibility and efficacy of previously developed BSIs.^88-91

Because health disparities are generally embedded in social or structural determinants of health, multilevel interventions that concomitantly examine influences on health at the individual, interpersonal, organizational, community and/or societal levels are best suited to improve sleep health in childhood.^92-94 Existing BSIs focus primarily at a single level (e.g., individual or interpersonal).^{95, 96} The lack of tailored education and multi-level approaches among existing BSIs along with the lack of inclusion of diverse, multi-ethnic families in BSI studies suggests a critical gap in pediatric sleep research. This gap is of concern because children from marginalized families have a higher prevalence of sleep deficiency^14-17 and are at increased risk for other health disparities that have been associated with sleep deficiency,^{19, 97} suggesting that sleep health promotion may play an important role in reducing health disparities.

It should be noted, however, that inclusive sampling in BSI studies may not be adequate and existing BSIs should be evaluated for their appropriateness and acceptability across diverse cultures. The development of tailored BSIs that meet the needs of diverse families requires interdisciplinary collaboration between scientists, providers, educators, and parents, followed by thorough testing of the efficacy of these interventions using protocols that include inclusive sampling. A recent study of real-world implementation of BSIs among a racially and ethnically diverse sample of families, found no differences in the initiation of BSIs between Hispanic, non-Hispanic Black, and non-Hispanic families, yet non-Hispanic Black families were significantly more likely to be informed about BSIs by pediatric providers and nearly five times more likely to discontinue a BSI prior to completion.⁹⁸

The interdependent dyadic relationship between parents and children is intrinsically linked with sleep health in early childhood. Poor sleep health in children results in stress and worsening mood in parents.^{99, 100} Parental well-being, including stress, distress, and depressive symptoms, generally improve concurrently with improvements in child sleep deficiency in behavioral sleep interventions (BSI) studies.^{85, 89, 101-103}

Discussion

Although adults have historically been the primary focus when examining sleep health, the critical importance of also investigating sleep in early childhood has more recently been identified.^{1, 3} The purpose of this review was to summarize the key advances in our understanding of sleep health in early childhood and the possible role of sleep deficiency during early childhood in the development of health disparities. Discussion of the current literature highlights the importance of assessing the multiple dimensions of children’s sleep health and conceptualizing sleep health within a social-ecological framework, understand how and when sleep may contribute to the development of health disparities, and the proposition that multilevel interventions are needed to combat the epidemic of sleep insufficiency in early childhood. The hope is that this paper may serve as a resource for sleep education, future research, and clinical consideration.

In addition to pediatric sleep deficiency being a problem in and of itself, the intersection of sleep insufficiency and physiological development poses a permanent risk in contributing to future health problems as highlighted in recent systematic and meta-reviews.^{19, 67, 104, 105} Children who experience sleep insufficiency are predicted to suffer from a myriad of other disease states, pediatric sleep problems have been identified as a risk for future health outcomes, and scientists and clinicians are more aware of approaches to address pediatric sleep insufficiency.

With the emerging concept of sleep as a multidimensional construct, multi-level interventions are also essential. When focusing on the individual, their immediate environment is considered, including a child’s education and care, relationship with parent(s) and other individuals, home environment and exposures, and community.¹⁰⁶ At the community and, furthermore, the societal level, it has become undeniable that there are significant socioeconomic disparities that play a role in sleep health.⁵⁵ Despite a relatively reduced availability of information in how to combat socioeconomic disparities and sleep, it is encouraging that there is further effort in studying and intervening in all populations, especially the most vulnerable.

Future interventions and areas of interest include continuing to focus on and define sleep as a pillar of health. This includes an all-encompassing scope of contributing factors to sleep health. It is critical to acknowledge the inextricable role of parental control and that socioecological influences on sleep health in early childhood are likely to be distinct from those in adolescence and adulthood. From an intervention standpoint, the home, childcare/schools, healthcare visits, and community resources all play an invaluable role in identification/diagnosis, education, and support for children and their families. Caring for children and families of all ethnicities, educational levels, and socioeconomic status is a crucial step, regardless of financial means, physical location, and access to resources. In the future, a movement towards standardizing education and care related to sleep may reduce this gap that occurs across individuals of varying populations.

Overall, all children and their families should have the means to recognize the importance of sleep health. This will require collaboration from parents, educators, researchers, and clinicians. This is driven by continued focus to further knowledge in the field of pediatric sleep health. The connection between rising healthcare burdens and sleep has become more evident. Addressing this health disparity in the pediatric stage may prove to be critical in improving health and quality of life, both presently and in the future.

KEY POINTS.

• Sleep deficiency in early childhood is a growing public health concern.

• Sleep in early childhood is influenced by social and ecological variables that are unique to those that influence adolescents and adults.

• Behavioral sleep interventions hold great promise in improving children's sleep health.

• Studies on behavioral sleep interventions lack inclusive sampling and more research is needed to develop and test multi-level interventions that can be personalized and tailored to meet the diverse population of young children.

SYNOPSIS.

There is growing public health concern about the high prevalence of sleep deficiency in early childhood and the associated risk for sleep-associated poor health outcomes, including metabolic, cardiovascular, and mental health. The recent shift to conceptualize sleep health as a multidimensional construct, influenced by socioecological factors, highlights the potential role of sleep in health disparities. Understanding the development of sleep health and the emergence of sleep disorders in early life is a current priority in pediatric sleep research. Future behavioral sleep interventions should consider the multiple socioecological influences on children’s sleep health and be tested using inclusive sampling methods.

Clinics Care Points:

• Sleep health is a low-cost, modifiable construct that may contribute to the development of health disparities early in life.

• History taking must include questions to assess the multi-dimensional constructs of sleep health to accurately develop a full understanding of children’s sleep deficiency.

• Socioeconomic status is a significant contributor to poor sleep outcomes and health of children and their families

• Behavioral sleep interventions in childhood should consider individual, familial, educational, clinical, community, and societal influences.