Cross-cultural research on infant sleep health

Over the first few years of life, sleep patterns rapidly develop, with many changes in sleep timing, consolidation, naps, and total (24-hour) sleep duration. ^, Although sleep is often conceptualized as a physiological phenomenon driven by biological need, a large body of evidence indicates that cultural and contextual factors play a major role in pediatric sleep patterns. ^, Norms and expectations of infant sleep are largely based on cultural expectations; that is, culture helps to determine what constitutes “normal” infant sleep. As such, acknowledging cultural differences in infant sleep patterns is critical for understanding variation in infant sleep health across contexts.

It can be challenging to make cross-cultural comparisons of infant sleep health due to methodological differences and a limited number of countries/regions included in the sampling. However, a few studies utilizing the same measures and procedures in a large number of countries/regions have been conducted and show stark differences across cultures. A study of 29,287 caregivers of infants ages 0 to 36 months across 17 countries found that infants and toddlers from “predominantly Asian (PA)” countries/regions (e.g., China, Korea, Vietnam) had significantly later bedtimes and later wake times than infants and toddlers in “predominantly Caucasian (PC)” countries/regions (e.g., United States, Australia, New Zealand). For example, bedtimes ranged from 19:27 (New Zealand) to 22:17 (Hong Kong), while wake times ranged from 5:56 (Indonesia) to 7:58 (Korea). On average, PA infants and toddlers were going to bed an hour later (21:26) than PC infants and toddlers (20:25).

Regarding other dimensions of sleep health, the same study found that PA infants and toddlers had significantly longer and more frequent night wakings than PC infants and toddlers. There was also variation within the PA group; for instance, infants and toddlers in Korea had fewer night wakings compared to infants and toddlers in other PA countries/regions, although night waking frequency was still increased relative to infants and toddlers in PC countries/regions. Infants and toddlers in PA countries also had significantly shorter sleep duration, both overnight and in a 24-hour period compared to infants and toddlers in PC countries/regions. Nighttime sleep duration ranged from 8.7 hours (Taiwan) to 10.6 hours (New Zealand) and total sleep duration ranged from 11.6 hours (Japan) to 13.3 hours (New Zealand). These differences in sleep duration have been examined longitudinally, with one study showing that young children in Singapore tend to exhibit shortened overnight and total sleep durations but a longer daytime sleep duration from ages 3 to 54 months compared to estimates of overnight sleep among “predominantly Caucasian” samples in other studies.

As noted above, it is important to examine variation in infant sleep health both across and within countries/regions. One study utilizing the same data from the broader PA and PC infant sleep research found that infants in Korea had even shorter total sleep duration (11.89 hours) and even later bedtimes (22:08) than infants and toddlers in both PA (12.33 hours, 21:25) and PC (13.02 hours, 20:25) countries/regions overall. Similarly, another study compared the sleep of infants in the broader PA sample to those from Japan, who showed fewer and shorter night awakenings and fewer and shorter naps compared to those of other Asian countries/regions.

Cross-cultural research on infant sleep health behaviors has also shown variation in the consistency and activities involved in bedtime routines. In the same cross-cultural studies referenced above, infants and toddlers from PA countries/regions were less likely to implement a consistent bedtime routine (implemented 5 or more nights/week) than those in PC countries/regions. Activities involved in bedtime routines, including book-reading, watching television, singing songs, and praying, also vary by country/region, and warrant further exploration both within and across contexts, given that research to date has shown a dose-response link between consistent bedtime routines and better early childhood sleep outcomes. As an example of cross-cultural variation within a single country, a recent study of infants and toddlers ages 3 to 36 months in Israel compared Arab and Jewish cultural groups on infant sleep patterns and ecology. Roomsharing and maternal involvement at bedtime were more prevalent among Arab families, with Arab children showing later bedtimes, longer night awakenings, and shorter nighttime sleep durations compared to Jewish children. Interestingly, whereas sleep onset latency was a strong correlate of nighttime sleep duration in Arab children, caregiver behaviors at bedtime were strong correlates of this outcome in Jewish children.

These findings underscore the importance of comparing cultures within a country/regional context, and converge with broader cross-cultural research, which has highlighted that caregiver bedtime presence and family sleep arrangements, in addition to bedtime routines, are associated with variation in early childhood sleep patterns. For instance, sleeping in a separate room was associated with a shorter sleep onset latency, fewer night wakings, and longer nighttime sleep duration, but these associations were stronger among infants in PC countries/regions, who were more likely to fall asleep independently, without caregiver presence, when sleeping in a separate room. By contrast, infants in PA countries/regions were more likely to fall asleep with a caregiver present, regardless of whether the infant slept in a separate or shared room.

Infant sleep health disparities

In addition to cross-cultural differences in infant sleep health, there is a growing body of research highlighting sleep health disparities by race, ethnicity, and SES. This research primarily examines infant sleep within instead of across countries/regions, with most studies conducted in the United States. Several studies have found that non-Hispanic/Latinx White (hereafter, “White”) infants and toddlers obtain more nighttime sleep compared to infants and toddlers of African American/Black (hereafter, “Black”), Hispanic/Latinx (hereafter, “Latinx”), and Asian racial and ethnic backgrounds. Racial and ethnic disparities in infant sleep duration have continued in the context of the coronavirus (COVID-19) pandemic, with a recent study showing shorter nighttime sleep duration in Latinx infants compared to their White counterparts during the ongoing pandemic.

A longitudinal study of infants over the first 2 years of life also found that overall, Black, Latinx, and Asian children showed a consistently shorter total (24-hour) sleep duration compared to White children. One study of predominantly racial and ethnic minoritized preschoolers from lower-SES backgrounds found that over 20% of caregivers reported that their child obtained insufficient total sleep duration (<10 hours), according to age-based US guidelines. Similarly, a longitudinal cohort study examining caregiver-reported child sleep duration of 1288 children at ages 6 months to 2 years, 3 to 4 years, and 5 to 7 years found that Black, Latinx, and Asian children were more likely to experience insufficient sleep than White children at each age. A recent study following 306 infants from age 1 month to 6 months found that Black and Latinx infants experienced smaller increases in nighttime sleep over this developmental period compared to White infants, with Asian infants experiencing more frequent night wakings relative to White infants. At the same time, studies have also shown that children of racial and ethnic minoritized backgrounds tend to obtain more sleep during the day (i.e., more frequent and longer naps) than White children. ^, Longer daytime sleep could compensate for the observed shorter nighttime sleep duration, or vice versa.

Notably, some of the racial and ethnic differences in infant sleep described above are partially attenuated when considering SES and other social and environmental factors. ^{, ,} For instance, in the longitudinal cohort study described above, racial and ethnic differences in sleep duration between ages 6 months and 7 years were diminished when considering lower maternal education level and household income, both of which were linked to insufficient sleep. Another study found that Latinx infants were three times more likely to obtain insufficient sleep based on sleep duration recommendations compared to White infants; however, these differences were attenuated when having a foreign-born mother, a lower maternal education level, and a later bedtime were included in analyses. Indeed, independent of racial and ethnic disparities in infant sleep health, there is mounting evidence of socioeconomic sleep disparities. In this research, SES is often indexed using a variety of individual and contextual economic indicators. Child or family-level SES is typically measured using one or a combination of variables such as household income, household poverty level (household size, income, and US poverty guidelines), and caregiver education level or occupational status. For example, several studies in addition to those referenced above have found shortened total infant sleep duration among those living in lower-income homes and/or whose caregivers have not graduated college compared to infants living in higher-income homes and/or with more highly educated caregivers. ^,

Other studies have used neighborhood-level indicators of SES, drawing upon available federal data sources, such as the US Census, to identify the average neighborhood income, proportion of families living in poverty, and other metrics. One study of 14,980 caregivers in the United States found later bedtimes, longer sleep onset latencies, and shorter sleep durations for infants living in the most distressed neighborhoods, compared to those in more advantaged neighborhoods, according to a neighborhood economic index based on multiple Census-derived indicators. Another study of 1226 mothers of 12-month-old infants examined infant sleep duration as a function of urbanicity, which is the proportion of urban land use. In this study, average infant sleep duration was shorter in higher quintiles of urbanicity. A recent systematic review found that, overall, lower neighborhood SES was associated with poorer sleep outcomes, including shorter sleep duration and later sleep timing, in young children ages 0 to 5 years. While aspects of the neighborhood social environment, such as crime and safety, were also associated with child sleep outcomes, these studies were conducted with school-aged children and adolescents.

Research on the unique contribution of neighborhood factors to infant sleep health disparities is mixed. In the cross-sectional study of infant sleep and urbanicity, living closer to major roadways and in densely populated neighborhoods were also associated with shorter infant sleep duration, but these associations were no longer significant when sociodemographic variables, such as prenatal tobacco smoke exposure and television viewing at age 1 year, were included in analyses. However, a study of 80 Black infants and their caregivers found that greater neighborhood deprivation was associated with increased infant actigraphy-derived night wakings, even after controlling for family-level sociodemographic factors, including maternal education, family poverty level, and a single-mother household. A Canadian study found that beyond infant ethnicity and family income, an index of neighborhood disorder, based on community-level crime reports, and maternal perceptions of an unsafe neighborhood were associated with less consolidated nighttime sleep among 12-month-old infants. In addition, a Canadian Census-derived neighborhood deprivation measure was indirectly linked to infant sleep consolidation, such that neighborhood deprivation was associated with more disorder and less safety, which in turn was associated with poorer sleep consolidation. While longitudinal research is needed to better understand these associations, these studies underscore the need to examine multiple family- and neighborhood-level SES indicators, along with family race and ethnicity data, when examining infant sleep health disparities.

Overall, there are fewer studies that examine disparities in dimensions of infant sleep health beyond sleep duration, efficiency, and timing. One study found that in families of lower-SES backgrounds, maternal race and ethnicity were related to child bedtime routine consistency, such that children of White mothers were the most likely (94.4%) to have a regular bedtime routine, followed by children of Latinx (89.7%) and Black (85.3%) mothers. In a study examining multilevel cumulative risk factors, including caregiver education, employment, income, and neighborhood-level SES, with each increase in the number of these sociodemographic risks, there was a 10% increase in the likelihood of poor early childhood sleep health behaviors, including the absence of a bedtime routine, caffeine consumption, insufficient sleep duration, and electronics present in the child’s bedroom, even when covarying for child race and ethnicity. Another study examining infant sleep health outcomes among caregivers of lower-SES backgrounds found that nearly half (49.6%) of caregivers had a TV in the room where the infant slept and 26.6% of caregivers reported inconsistent infant nap and bedtimes. Further, lower caregiver health literacy was associated with greater likelihood of having a TV in the infant’s bedroom, as well as greater likelihood of insufficient infant sleep duration. A longitudinal study following children from 6 months to 7 years found that having a TV in the bedroom at any point during the study was more common among racial and ethnic minoritized children compared to White children. Interestingly, although the effect of lifetime TV viewing on child sleep duration longitudinally did not vary by race and ethnicity, the presence of a TV in the bedroom did, such that having a TV in the bedroom was associated with a 32-minute shorter sleep duration in minoritized children, but not among White children.

Cross-cultural differences in behavioral infant sleep problems

Broadly defined behavioral sleep problems are very common in infancy and early childhood, with studies indicating that 15% to 30% of children experience caregiver-identified sleep problems in the first few years of life. Infant sleep problems are often assessed using a single question directed to caregivers. For instance, the Brief Infant Sleep Questionnaire (BISQ), a widely used infant sleep assessment measure, asks caregivers to rate whether they consider their child’s sleep to be a problem on a Likert scale ranging from not a problem to a serious problem. Frequent night awakenings are a common correlate of caregiver-identified infant sleep problems, ^, although some research suggests there may be cross-cultural variation in both the prevalence and correlates of infant sleep problems.

The previously discussed cross-cultural research comparing infant sleep patterns and problems in 17 countries/regions found that caregivers in PA countries/regions were more likely to consider their infant’s sleep a problem than caregivers in PC countries/regions (51.9% versus 26.3%, respectively) ; this was also the case when examining the prevalence of a “severe” infant sleep problem (17% in PA versus 2% in PC countries/regions). PA caregivers (22.3%) were also more likely to endorse child bedtime difficulty compared to PC caregivers (14.3%). A follow-up study examining sleep problem correlates in this sample found that overall frequency of night wakings and cultural context were the strongest predictors of a severe sleep problem. That is, caregivers from PA countries/regions were 6.5 times more likely to report a child sleep problem than caregivers from PC countries/regions. Interestingly, in PC countries/regions child night waking frequency and sleep onset latency were the strongest correlates of a child sleep problem, whereas in PA countries/regions, sociodemographic characteristics, such as child and caregiver age, were most strongly linked to a child sleep problem. Variation in caregiver-perceived child sleep problems may reflect cultural differences in expectations for “normal” versus “problematic” sleep, as well as differences in the perceived impact of child sleep on family functioning. For instance, in 10,085 mothers of young children across 13 different countries/regions, similarly divided into PA versus PC groups, mothers’ own sleep was more robustly associated with the perception of her child’s sleep as being problematic in PC compared to PA countries/regions.

As with research on infant sleep patterns, findings from this cross-cultural sample showed some within-country/region variation in caregiver-reported sleep problems. For instance, caregivers from Japan were less likely to endorse an infant sleep problem (19.6%) compared to the rest of the PA group (53.3%) but were more likely to report bedtime difficulties. In Korea, fewer severe sleep problems (2.3%) were reported compared to other PA countries/regions (18.1%), with severe sleep problem endorsement more comparable to those in PC countries/regions. In a smaller study examining infant and toddler sleep in Australia and New Zealand, close to one-third of caregivers reported a child sleep problem, which was comparable to rates in these countries drawn from the larger cross-cultural study. Another study found that 49% of infants and toddlers in Spain had a caregiver-identified sleep problem, which was associated with shorter child sleep duration and more frequent and longer night wakings. In a cross-cultural study of Arab and Jewish families in Israel, 14.1% of Arab mothers perceived their 3- to 18-month-old child’s sleep to be a problem compared to 4.29% of Jewish mothers, with notable differences in the degree of caregiver bedtime involvement, the sleep ecology, and infant sleep patterns between these cultural groups.

Disparities in behavioral infant sleep problems

Few studies have examined disparities in broadly defined, caregiver-perceived behavioral sleep problems and symptoms in young children, especially during infancy. This literature gap is also found in behavioral sleep treatment research, where few studies have included families of racial and ethnic minoritized and/or lower-SES backgrounds, underscoring the need for additional studies of disparities in both infant behavioral sleep problem identification and treatment. In the United States, there is some initial evidence that White caregivers are more likely to report early childhood sleep problems than caregivers of racial or ethnic minoritized backgrounds. White mothers of preschoolers reported significantly more concerns about their child having sleep onset difficulties (38%) compared to Black mothers (28%), but not Latinx mothers (33%). A retrospective study examining pediatric sleep disorders diagnosed in well child visits found that infants and toddlers of Black and “other” racial and ethnic backgrounds were less likely to have received any (medical or behavioral) sleep disorder diagnosis compared to White infants and toddlers.

A large-scale study of 14,980 caregivers found that caregivers from more socioeconomically distressed neighborhoods, defined using US Census data, were less likely to endorse an infant/toddler sleep problem (42.6%) compared to caregivers from more advantaged neighborhoods (57.9%), despite caregivers in distressed neighborhoods being more likely to report poorer child sleep outcomes, including a longer sleep onset latency and shorter sleep duration. A follow-up study using the same sample demonstrated that although correlates of a caregiver-endorsed child sleep problem were similar across levels of neighborhood distress, the perceived impact of child sleep on caregiver sleep was more robustly associated with a child sleep problem in more advantaged neighborhoods. Importantly, however, information about family-level SES, race, and ethnicity were not available in the dataset. In one of the few studies to examine specific symptoms of insomnia in young children, increased exposure to cumulative sociodemographic risk factors, including family and neighborhood disadvantage, was associated with greater likelihood of caregiver-reported insomnia symptoms in young children, covarying for child race and ethnicity. Of note, however, overall rates of caregiver-perceived sleep problems (15.1%) were lower than anticipated based on previous research.

Disparities in medical infant sleep problems

The vast majority of research on disparities in medical sleep disorders in pediatrics has been conducted with school-aged children and adolescents, with a focus on sleep-disordered breathing (SDB). SDB reflects a continuum of breathing difficulties during sleep, from obstructive sleep apnea (OSA), which is the most severe form of SDB, to mild snoring. Pediatric SDB is found in between 10.5% and 17.1% of children, with 1% to 3% experiencing OSA. Research on older children indicates that Black youth are approximately four to six times more likely than White youth to experience SDB. ^, The sparse early childhood literature indicates similar racial disparities, although smaller in magnitude. A study of infants and toddlers found that Black children were significantly more likely to snore 3 or more times/week than White children (25% versus 15%, respectively). Another study found that Black preschoolers were 2.5 times as likely as White preschoolers to exhibit caregiver-reported SDB symptoms, while Latinx preschoolers were 2.3 times as likely as White preschoolers to exhibit these symptoms. School-aged Black children diagnosed with OSA have also shown increased disease severity (measured by apnea-hypopnea index) on polysomnogram compared to White children with OSA, controlling for other OSA risk factors such as prematurity. Independent of race and ethnicity, SES has also been associated with SDB, such that children from lower-SES homes and/or neighborhoods are more likely to experience SDB than those living in more advantaged contexts.

There are additional racial, ethnic, and socioeconomic disparities in the treatment of OSA, potentially reflecting differential access to and experiences with pediatric health care. For instance, a number of studies in older youth indicate lower rates of OSA treatment via adenotonsillectomy, the primary treatment approach, in Black and Latinx compared to White youth. ^, A study using state health care data found that in addition to lower rates of adenotonsillectomy in Black and Latinx children, there were also lower rates of adenotonsillectomy in children who were publicly insured compared to those with private insurance, suggesting income-related disparities. Another study in a smaller sample found that children who were publicly insured experienced increased delays in SDB treatment, including initial polysomnogram and surgical treatment, than privately insured children. Although in older children, there is also preliminary evidence that the benefits of adenotonsillectomy for treating OSA and its neurobehavioral symptoms may be diminished in Black youth compared to those of White and other racial and ethnic backgrounds. However, more research is needed on disparities in the identification and treatment of SDB, as well as other medical sleep disorders, in infancy and early childhood, especially as medical symptoms and treatment approaches may differ substantially for infants and toddlers compared to youth of older ages.

Multilevel contributors to infant sleep disparities

A 2020 NIMHD workshop report on sleep health disparities highlighted the need to identify and test multilevel and multifactorial interventions to address these disparities. A socioecological framework is well-suited for understanding the multiple and interactive factors at different social and ecological levels that contribute to sleep health disparities, and this model has been previously applied to sleep patterns, problems, and disparities across the lifespan. ^{, ,} Briefly, within this model there are microsystem factors, or individual child characteristics, that interact with factors in the mesosystem (e.g., family/home, school, health care, and neighborhood environments) and macrosystem (e.g., broader social, cultural, and political climate), which also interact within and across levels to contribute to developmental outcomes and disparities. In the sections that follow, we summarize selected socioecological factors that have been associated with infant sleep patterns and problems and could contribute to or buffer against infant sleep disparities. The socioecological factors described below are not an exhaustive list of putative mechanisms, and future research is needed to understand the multifactorial and multilevel nature of sleep health disparities in infancy.

Future directions

There are a number of directions for future research on infant sleep health disparities and cross-cultural differences. Most of the research to date on infant sleep disparities focuses on Black-White differences or SES, with fewer studies focusing on other health disparity populations, such as Asian and Latinx infants or families living in rural contexts. In addition to the limited knowledge of other health disparity populations, there is also a lack of research on the intersecting nature of these disparities. Intersectionality, a term coined by legal scholar Kimberlé Crenshaw, refers to a framework that considers the multilayered and overlapping identities that inform an individual’s experience in society. To apply intersectionality theory to pediatric sleep health research, one might examine sleep outcomes in young children of racial and ethnic minoritized backgrounds who also experience neurodevelopmental differences and are living in lower-SES homes. There is a need for more pediatric sleep research using this intersectional lens, as all individuals have overlapping identities that inform health outcomes and focusing on only one aspect of an individual’s identity likely overlooks critical nuances. Another important but often excluded population is fathers. The majority of infant sleep research focuses on mothers and infants, with few studies examining the role of fathers in relation to infant sleep outcomes. There is some evidence that paternal involvement positively impacts infant sleep outcomes, but more research involving fathers, especially in treatment studies, is necessary.

There are also methodological limitations in infant sleep health disparities research. Longitudinal studies examining determinants of infant medical and behavioral sleep disorders and disparities are needed, given that sleep patterns change drastically and rapidly over the first few years of life. Most of the available research is cross-sectional, which limits the identification and evaluation of potential causal mechanisms of infant sleep health disparities. Mechanistic research is additionally needed to better understand how determinants of infant sleep health disparities unfold, interact, and evolve over time. Such research can inform the much-needed multilevel treatment strategies for sleep health equity promotion, particularly when modifiable factors are identified.

There is also limited qualitative and mixed methods research considering family perspectives on cultural norms around infant sleep, as well as treatment for medical and behavioral sleep disorders. In a recent qualitative study, caregivers and primary care clinicians identified a lack of knowledge of early childhood sleep-related recommendations, which may inform expectations of normative versus problematic sleep across different populations. Another qualitative study found that mothers from lower-SES backgrounds reported applying the bedtime routine and other sleep strategies they had learned from their own families to their young children’s sleep, indicating a legacy of cultural sleep beliefs. Caregiver perspectives from each of these studies also suggested that adaptations to address social and contextual factors (e.g., caregiver work schedules, family sleep beliefs) are needed in behavioral sleep interventions. In a rare qualitative study of family decision-making in treatment for pediatric SDB, caregivers expressed the importance of trust in their physician when identifying the best course of treatment. Collectively, these studies underscore the value of soliciting family perspectives in pediatric sleep research, as these qualitative data can provide insights into sleep intervention foci and adaptations for health disparity populations.

Much of the infant sleep health disparities studies to date have focused on describing the nature and extent of these disparities. Although additional research on determinants of these disparities is needed, there is also a paucity of interventional research for behavioral sleep problems in health disparity populations. A recent systematic review of behavioral sleep interventions found that less than half of intervention studies reported family race and ethnicity, and of those studies, 78% of participants were White. Furthermore, most caregivers included had moderate to high levels of education. Without more diverse participants included in these studies, results of interventions may lack generalizability. Recently, however, a secondary analysis of randomized clinical trial with Black mothers and infants found evidence of longer total infant sleep duration and fewer nighttime awakenings at 16 weeks of age among dyads that received a responsive parenting intervention compared to those who received a safety control condition. Future research should also focus on designing and/or adapting early childhood behavioral sleep treatment strategies as well as broad sleep health promotion efforts in collaboration with families from health disparity populations. Community-engaged research strategies may be especially beneficial in this regard. Initial research on an early childhood behavioral sleep treatment adapted for families from lower-SES and/or racial and ethnic minoritized backgrounds has demonstrated that a community-engaged approach to intervention adaptation is feasible, with families endorsing high levels of intervention acceptability and cultural humility.

Conclusion

There are salient cross-cultural differences in infant sleep patterns and problems as well as important racial, ethnic, and socioeconomic sleep health disparities. The evidence of cross-cultural variation in sleep patterns and perceptions of infant sleep problems highlights the notion that infant sleep is determined by multiple factors, including biological needs, cultural norms and expectations of child sleep, and the family context. Considering these and additional factors at multiple socioecological levels is necessary to understand and effectively address infant sleep health disparities. To promote sleep health equity, future research should include an intersectional framework, longitudinal and qualitative designs, as well as a focus on intervention design, adaptation, and evaluation with sociodemographically diverse and health disparity populations.