The Intersect of Biology and Culture in Shaping Children's Sleep

In this issue of SLEEP, Hense and colleagues provide valuable data regarding determinants of parent-reported sleep duration of children ages 2 to 9 years across 8 European countries.¹ The authors demonstrate a significant effect of country of origin on children's parent-reported sleep durations, which seemed to overlay individual-level predictors of sleep duration.

This study has a number of significant strengths. First, the sample size is unparalleled and provides unprecedented power to detect small but significant effects on sleep duration among children. Secondly, as the authors point out, by using a standard measure across countries, the study makes progress towards understanding if differences across countries are “real”, as opposed to simply due to differences in measurement approach. This study also provides the opportunity to determine if previously identified individual determinants of sleep duration among children hold true across countries. A consistent relationship would support the robustness, and possibly underlying biological mechanism, of these predictors in affecting sleep duration. Another significant strength of this study is the fact that the children's weights and heights were actually measured, as opposed to parent-reported, since the accuracy of parent-reported child weight and height is debated.² Likewise, the accurate measurement of children's physical activity is also a significant methodological challenge,³ and a study sample of this large size using actual accelerometry data is invaluable.

Before considering the implications of the study findings, the possibility that the observed cross-country differences may be a function of the measurement being “lost in translation” must be considered. Though Hense et al. did an admirable job of translating and back-translating the interview questions across languages and countries, the possibility still remains that the meaning of these questions differed subtly across countries. Previous work by others in areas unrelated to sleep has highlighted the differences in understanding of common health-related terms or concepts between researchers or clinicians and patients, even within a single culture.^4,5 Future ethnographic work might attempt to better understand the meaning of sleep-related questions across languages and cultures. At the most basic level, the actual meaning of “getting up in the morning” and “going to bed” may have subtly different meanings across cultures and languages that are not captured by different available vocabulary words. On another level, although the words may mean the same thing, the meaning of a child having “good sleep”, and how it reflects on parenting, may vary across cultures, and thereby lead to different types of response bias. For example, in cultures in which a child having a relatively late bedtime would be considered a marker for “poor,” “neglectful,” or “permissive” parenting, individual respondents may be less likely to accurately report a later bedtime for the child. Future work with more objective measures of sleep, such as actigraphy, would help to address this issue.

The central question raised by the findings of Hense et al. is the root cause of the cross-country differences. Assuming that the differences are real, one must consider if the cross-country differences are driven by nature, nurture, or their interaction. Specifically, nature might contribute to sleep duration through genetics⁶; these genetic differences may cluster within ethnic groups within countries and thereby account for some of the differences observed across countries. Alternatively, the primary cause for the cross-country differences may instead be “nurture“, meaning that environment or culture is playing the primary role. The most sophisticated and probably most appropriate conceptualization of the cross-country differences may be an interaction of nature and nurture, commonly referred to as “the transactional model” in the child development literature.⁷ Specifically, a child's biologically driven sleep behavior affects parenting around sleep, but the parenting around sleep also shapes the biology of sleep.

The profound influence of culture on sleep that the findings of Hense et al.¹ highlight is briefly touched upon in their discussion and reference to a paper by Owens⁸ describing the relationship between sleep and culture among children. The Owens paper introduced a supplement to the journal Pediatrics published in 2005⁹; the supplement attempts to review cultural contributors to children's sleep, while outlining the significant limitations of the current literature. A comprehensive review included in this supplement by Jenni and O'Connor outlines the myriad ways in which biology and culture intersect to affect children's sleep, as well as to affect whether that sleep is perceived as a problem, across cultures.¹⁰ When thinking of culture and sleep among children, the most common example detailed is that of co-sleeping during infancy. However, as reviewed by Jenni and O'Connor, the variability is much greater and all-encompassing. For example, sleep patterning (whether sleep is consolidated at night, amount of napping, duration of nighttime awakenings, etc.) differs dramatically across cultures and is one of several explanations for the findings of Hense et al.¹ Specifically, the shorter nocturnal weekday sleep duration noted in Hense et al. in some countries may not indicate shorter total sleep duration over the course of a week, but simply less sleep during weekday nights in some countries, with compensation for “sleep debt” occurring during culturally “endorsed” and “accepted” naps and weekend sleep. Another possibility, as Jenni and O'Connor review, is that the shorter sleep duration in some countries may reflect expectations placed on the child for “industriousness” that encourage achievement at the expense of sleep duration. Finally, while some cultures expect children to fall asleep independently and relatively early in the evening to provide adults more private time away from the children, other cultures integrate children fully into adult routines, often also co-sleeping. How these cultural expectations do or do not match the child's own innate sleep biology will translate to longer and shorter sleep durations for the individual child, and possibly for children as a group within a culture.

In summary, the findings of Hense et al.¹ highlight the need for improved measurement of sleep. More importantly, however, they highlight the need for an improved understanding of cultural influences on children's sleep, and how those cultural influences both respond to and shape the biology of sleep.

DISCLOSURE STATEMENT

Dr. Lumeng has indicated no financial conflicts of interest.