Genetic and environmental influences on daytime and nighttime sleep duration in early childhood

Distal skin vasodilation promotes rapid sleep onset in preterm neonates

Although sleep is of paramount importance for preterm neonates, care of the latter in a neonatal intensive care unit does not favour sleep. Given that several studies in adults have described a 'vegetative preparedness to sleep' (in which distal skin vasodilation before lights-out promotes rapid sleep onset), we looked at whether or not this process operates in preterm neonates. Sleep propensity was assessed in terms of the duration of a spontaneous episode of wakefulness (W). Skin temperatures at six body sites (the abdomen, pectoral region, eye, hand, thigh and foot) were measured (using infrared thermography) during nocturnal polysomnography in 29 9-day-old preterm neonates (postmenstrual age: 209 ± 9 days). We then determined whether the duration of the W episode depended upon the local skin temperatures measured at the start, during and end of the episode. The W episode was shorter when distal skin temperatures (thigh, hand and foot) and the pectoral temperature were higher at the end of the episode (i.e. at sleep onset). The relationship with the duration of the W episode was not significant for temperatures measured at the start of the W episode. We observed gradual distal vasodilation at the pectoral region, the thigh, hand and foot (i.e. affecting most of the body's skin surface) during W episodes. Our results constitute initial evidence to show that distal vasodilation may have a key role in facilitating sleep onset in very preterm neonates.

Mandatory Nap Times and Group Napping Patterns in Child Care: An Observational Study

Policy provision for naps is typical in child care settings, but there is variability in the practices employed. One practice that might modify children's early sleep patterns is the allocation of a mandatory nap time in which all children are required to lie on their beds without alternate activity permitted. There is currently limited evidence of the effects of such practices on children's napping patterns. This study examined the association between duration of mandatory nap times and group-level napping patterns in child care settings. Observations were undertaken in a community sample of 113 preschool rooms with a scheduled nap time (N = 2,114 children). Results showed that 83.5% of child care settings implemented a mandatory nap time (range = 15-145 min) while 14.2% provided alternate activities for children throughout the nap time period. Overall, 31% of children napped during nap times. Compared to rooms with ≤ 30 min of mandatory nap time, rooms with 31-60 min and > 60 min of mandatory nap time had a two-and-a-half and fourfold increase, respectively, in the proportion of children napping. Nap onset latency did not significantly differ across groups. Among preschool children, exposure to longer mandatory nap times in child care may increase incidence of napping.

Heritability and Genome-Wide Association Analyses of Sleep Duration in Children: The EAGLE Consortium

STUDY OBJECTIVES

Low or excessive sleep duration has been associated with multiple outcomes, but the biology behind these associations remains elusive. Specifically, genetic studies in children are scarce. In this study, we aimed to: (1) estimate the proportion of genetic variance of sleep duration in children attributed to common single nucleotide polymorphisms (SNPs), (2) identify novel SNPs associated with sleep duration in children, and (3) investigate the genetic overlap of sleep duration in children and related metabolic and psychiatric traits.

METHODS

We performed a population-based molecular genetic study, using data form the EArly Genetics and Life course Epidemiology (EAGLE) Consortium. 10,554 children of European ancestry were included in the discovery, and 1,250 children in the replication phase.

RESULTS

We found evidence of significant but modest SNP heritability of sleep duration in children (SNP h² 0.14, 95% CI [0.05, 0.23]) using the LD score regression method. A novel region at chromosome 11q13.4 (top SNP: rs74506765, P = 2.27e-08) was associated with sleep duration in children, but this was not replicated in independent studies. Nominally significant genetic overlap was only found (rG = 0.23, P = 0.05) between sleep duration in children and type 2 diabetes in adults, supporting the hypothesis of a common pathogenic mechanism.

CONCLUSIONS

The significant SNP heritability of sleep duration in children and the suggestive genetic overlap with type 2 diabetes support the search for genetic mechanisms linking sleep duration in children to multiple outcomes in health and disease.

Napping: A public health issue. From epidemiological to laboratory studies

Sleep specialists have proposed measures to counteract the negative short- and long-term consequences of sleep debt, and some have suggested the nap as a potential and powerful "public health tool". Here, we address this countermeasure aspect of napping viewed as an action against sleep deprivation rather than an action associated with poor health. We review the physiological functions that have been associated positively with napping in both public health and clinical settings (sleep-related accidents, work and school, and cardiovascular risk) and in laboratory-based studies with potential public health issues (cognitive performance, stress, immune function and pain sensitivity). We also discuss the circumstances in which napping-depending on several factors, including nap duration, frequency, and age-could be a potential public health tool and a countermeasure for sleep loss in terms of reducing accidents and cardiovascular events and improving sleep-restriction-sensitive working performance. However, the impact of napping and the nature of the sleep stage(s) involved still need to be evaluated, especially from the perspective of coping strategies in populations with chronic sleep debt, such as night and shift workers.

Emotional availability at bedtime, infant temperament, and infant sleep development from one to six months

Infant sleep consolidates rapidly during the first half year of life in the context of a dynamic, bidirectional exchange between infant characteristics and the caregiving environment. The current study examined the relationship between mothers' emotional availability (EA) at bedtime and infant temperament, and objectively assessing infant sleep development from one to six months, particularly focus on whether infant temperament moderated linkages between EA at bedtime and infant sleep development. The sample consisted of 72 mother-infant dyads, and the measures included actigraphy-assessed infant sleep at one and six months, observed maternal EA coded from bedtime videos at 3 and 6 months, and maternal reports of infant temperament at three and six months. The analysis showed significant positive effects of maternal EA at bedtime on developmental changes in infant sleep minutes. Additionally, infant temperamental surgency moderated the influence of EA at bedtime on the increase in infant sleep minutes. In other words, highly surgent infants whose mothers were emotionally available at bedtime showed a greater increase in their sleep time than other infants. The results are discussed in terms of the transactional model of infant sleep development.

[A prospective study of the development of nocturnal sleep patterns in infants]

OBJECTIVE

To investigate the development of nocturnal sleep pattern in infants.

METHODS

Fifty healthy full-term newborns born in Chongqing Maternal and Child Health Care Hospital were chosen for a prospective longitudinal study. A non-invasive sleep monitor, Actiwatch, was used to monitor infants' 12 sleep parameters on the 10th day, 28th day, the first Tuesday at the 2nd, 3rd, 4th, 5th, 6th, 9th and 12th month after birth, each monitoring time lasting 60 hours. All sleep parameters were analyzed by two-level mixed effect model.

RESULTS

Twenty-two boys and 25 girls completed the whole follow-up study. From birth to the 12th month after birth, the nocturnal sleep onset latency (NSOL) decreased by about 48% at 3 months of age and by 83% at 6 months of age. The nocturnal sleep efficiency (NSE%) increased from 66% to 87%, the nocturnal total sleep time (NTST) increased from 416 minutes to 517 minutes, and the longest nocturnal continuous sleeping time (L-NCST) increased from 197 minutes to 327 minutes. NSE%, NTST and L-NCST increased with age (P<0.01). The 3rd to 12th month ratios of NSE%, NTST and L-NCST were 86%, 84% and 72%, respectively, and the 6th to 12th month ratios of those were 97%, 91% and 94%, respectively. The nocturnal total wake time (NTWT) and longest nocturnal continuous waking times (L-NCWT) decreased with age (P<0.01). The decline speeds in the first half year were 5-6 times of those in the second half year after birth (P<0.05). NTST, nocturnal continuous sleeping ability and NSE% in boys were lower than those in girls (P<0.05).

CONCLUSIONS

Infantile nocturnal sleep patterns develop rapidly during the first 6 months, especially within the first 3 months after birth. Partial infantile sleep parameters are related to gender.

Mandatory Naptimes in Child Care and Children's Nighttime Sleep

OBJECTIVES

To examine the relationship between mandatory naptimes in child care and children's nighttime sleep duration, both concurrently and 12 months later once in school.

METHODS

A sample of 168 children (50-72 months; 55% males) attending licensed child care centers were observed across their morning and throughout their scheduled naptime. Mandatory naptime was determined as the period in which children were not permitted any alternative activity except lying on their bed. Teachers reported each child's napping in child care. Nighttime and total sleep duration was reported by parents at 2 time points, in child care and in the second semester of their first school year. General linear models were used to examine group differences in sleep duration between children experiencing 0 to 60 minutes and >60 minutes of mandatory naptime, adjusting for key confounders. Path analysis was conducted to test a mediation model in which mandatory naptime is associated with nighttime sleep duration through increased napping in child care.

RESULTS

Children who experienced >60 minutes of mandatory naptime in child care had significantly less nighttime sleep than those with 0 to 60 minutes of mandatory naptime. This difference persisted at 12-month follow-up, once children were in school. Napping in child care mediated the relationship between mandatory naptime and duration of nighttime sleep.

CONCLUSIONS

Exposure to mandatory naptimes of >60 minutes in child care is associated with decreased duration of nighttime sleep that endures beyond child care attendance. Given the large number of children who attend child care, sleep practices within these settings present an important focus for child health.

Longitudinal study of sleep behavior in normal infants during the first year of life

STUDY OBJECTIVES

To longitudinally examine sleep patterns, habits, and parent-reported sleep problems during the first year of life.

METHODS

Seven hundred four parent/child pairs participated in a longitudinal cohort study. Structured interview recording general demographic data, feeding habits, intercurrent diseases, family history, sleep habits, and parental evaluation of the infant's sleep carried out at 1, 3, 6, 9, and 12 months.

RESULTS

Nocturnal, daytime, and total sleep duration showed a high inter-individual variability in the first year of life associated with changes in the first 6 months and stability from 6 to 12 months. Bedtime was at around 22:00 and remained stable at 6, 9, and 12 months of age. Approximately 20% of the infants had more than 2 awakenings and slept more often in the parent bed. Nearly 10% of the infants were considered as having a problematic sleep by parents and this significantly correlated with nocturnal awakenings and difficulties falling asleep.

CONCLUSIONS

Sleep patterns change during the first year of life but most sleep variables (i.e., sleep latency and duration) show little variation from 6 to 12 months. Our data provide a context for clinicians to discuss sleep issues with parents and suggest that prevention efforts should focus to the first 3-6 months, since sleep patterns show stability from that time point to 12 months.

Examining the Interface of Children’s Sleep, Executive Functioning, and Caregiving Relationships

Research in developmental psychology is increasingly showing that children’s biology, cognition, and social relationships, which have often been studied separately, are in fact closely tied and influence each other in complex ways. This article summarizes work by our team and others on the connections among young children’s sleep, their executive functioning, and the quality of their caregiving relationships. Overall, children exposed to higher-quality parenting perform better on executive tasks and get sleep of higher quality or duration. In turn, sleep relates to subsequent executive performance, while also modulating the links between parenting and child outcomes. We propose directions for future research to address causal relations and to better pinpoint the direction and magnitude of the associations between these areas of child development.

Predictors of shorter sleep in early childhood

Objective

The aim of this study was to identify socio-demographic and home environmental predictors of shorter sleep in early childhood, and to examine whether effects were mediated by the timing of bedtime or wake time.

Methods

Participants were from Gemini, a British birth cohort of twins, and included 1702 children; one randomly selected from each twin pair. Parents reported night-time sleep duration at an average age of 15.8 months (range 14–27 months) using a modified version of the Brief Infant Sleep Questionnaire. Multiple logistic regression models were used to identify predictors of shorter sleep for this study.

Results

Using a cut-off of <11 h a night, shorter sleep was reported in 14.1% of children. Lower maternal education, non-white ethnic background, being male, low birth weight, living in a home with >1 older child and watching >1 h of TV in the evening were independently associated with shorter sleep. Mediation analyses showed that associations between education, ethnicity, evening TV viewing and sleep were driven predominantly by later bedtimes, while sex differences were driven predominantly by earlier wake times in boys.

Conclusion

In this sample, multiple environmental factors were associated with shorter sleep in young children, with several operating predominantly through later bedtime. An emphasis on the importance of an early and consistent bedtime could help promote healthy sleep and reduce inequalities in child health.