- Email: [email protected]
Infant night sleep trajectory from age 3–24 months: evidence from the Singapore GUSTO study
Accepted Manuscript Infant night sleep trajectory from age 3 to 24 months: Evidence from the Singapore GUSTO study Shaun K.Y. Goh, Elaine KH. Tham, Daniel YT. Goh, Teoh Oon Hoe, Seang Mei Saw, Fabian Yap, Yap-Seng Chong, Anqi Qiu, Birit FP. Broekman PII:
S1389-9457(17)30048-5
DOI:
10.1016/j.sleep.2017.01.013
Reference:
SLEEP 3300
To appear in:
Sleep Medicine
Received Date: 1 October 2016 Revised Date:
19 January 2017
Accepted Date: 22 January 2017
Please cite this article as: Goh SKY, Tham EK, Goh DY, Hoe TO, Saw SM, Yap F, Chong Y-S, Qiu A, Broekman BF, Infant night sleep trajectory from age 3 to 24 months: Evidence from the Singapore GUSTO study, Sleep Medicine (2017), doi: 10.1016/j.sleep.2017.01.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Infant night sleep trajectory from age 3 to 24 months: Evidence from the Singapore
RI PT
GUSTO study
Shaun K.Y. Goha, Elaine KH Thamb, Daniel YT Gohc, Teoh Oon Hoed, Seang Mei Sawe, Fabian
Department of Bioengineering and Clinical Imaging Research Center, National University of
M AN U
a
SC
Yapd, Yap-Seng Chongb,f, Anqi Qiua,b, Birit FP Broekmanb,*
Singapore, Singapore b
Singapore Institute for Clinical Sciences, Agency for Science and Technology Research
(A*STAR), Brenner Centre for Molecular Medicine, Singapore
Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore,
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c
National University Health System, Singapore
KK Women’s and Children’s Hospital, Singapore
e
Saw Swee Hock School of Public Health, National University of Singapore, Singapore
f
Department of Obstetrics & Gynaecology, Yong Loo Lin School of Medicine, National
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EP
d
University of Singapore, National University Health System, Singapore
S.K.Y.G. and E.K.H.T. contributed equally to this work
1
ACCEPTED MANUSCRIPT
ARTICLE INFO Article history:
RI PT
Received Received in revised form
SC
Accepted
M AN U
Keywords: Infant sleep
Latent growth curves
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Trajectory
EP
*Corresponding author at: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Brenner Centre for Molecular Medicine, 30 Medical
AC C
Drive, Singapore 117609, Singapore. Tel.: 0065 90095444; fax: 0065 6776 6840. E-mail address: [email protected] (B.F.P. Broekman)
2
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ABSTRACT Objective: Longitudinal studies on night sleep trajectories throughout infancy are sparse.
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Moreover, most studies have examined samples in Caucasian individuals, although cultural differences in sleep habits have been described. To expand on the current literature, we aimed to determine night sleep trajectories in an Asian population from age 3 to 24 months.
SC
Methods: Night sleep duration from a subset of 893 infants within the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort study was determined using the caregiver-
M AN U
reported Brief Infant Sleep Questionnaire. Latent growth curves were used to analyze sleep trajectories at 3, 6, 9, 12, 18, and 24 months.
Results: The overall trajectory was modeled with a piecewise model with two freely estimated curves. In the first phase (age 3−12 months), infants displayed an average curvilinear increase in
TE D
night sleep trajectories of 0.12 hour per month. In the second phase (age 12−24 months), infants continued to display a curvilinear increase, but at a slower average rate of 0.02 hour per month. Conclusions: The sleep trajectory of Singaporean infants appeared similar to other
EP
predominantly Caucasian cohorts for 3−12 months but not for 12−24 months, in which infants
AC C
from predominantly Caucasian cohorts mostly displayed a decreasing or a stable-plateaued trajectory. This is in concordance with existing studies that suggest that the underlying influences of night sleep shift from predominantly biological influences to increasing environmental influences with age.
3
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1.
Introduction
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Infant night sleep duration is known to be important to subsequent developmental and health outcomes such as cognitive and motor development [1], behavioural problems [2], and obesity risk [3]. However, unlike day sleep duration [4–7], development of night sleep duration
SC
throughout infancy is not well known.
First of all, studies on night sleep duration in infancy are sparse [4,6–8]. Aside from large
M AN U
cross-sectional studies that report increases in night sleep across the first year [4,7], to date there have been only two longitudinal studies that explicitly report night sleep longitudinally beyond the first year of infancy. The Zurich Longitudinal Studies reported that night sleep trajectories, after an increase in the first year of life, showed a subsequent curvilinear decrease until
TE D
adolescence [6]. However, the Quebec Newborn Twin Study reported a curvilinear increase in sleep from 6 to 48 months [8,9]. In summary, although few in number, existing studies suggest an overall increase in the level of night sleep until 1 year of age, but are less consistent in their
EP
findings after the first year.
AC C
Moreover, these findings are mainly from predominantly Caucasian samples, although previous cross-cultural studies [10–12] found differences of large effect size in night sleep duration among predominantly Caucasian samples compared to predominantly Asian samples [10]. Hence, it remains unclear how the level of night sleep develops within individuals across infancy and whether existing published trajectories are applicable to non-Caucasian samples. Infant night sleep plays a role in a range of health and developmental outcomes [1–3]. Interestingly, cross-sectional data have revealed differences in night sleep duration between 4
ACCEPTED MANUSCRIPT
predominantly Caucasian and predominantly Asian populations [10]. Hence, understanding the longitudinal developmental trajectory patterns of sleep among infants of different cultural backgrounds is important to inform clinicians and (local) clinical guidelines in sleep medicine,
RI PT
including possible cultural differences in these. Here we expand on the existing knowledge to understand the trajectory of infant night sleep in an Asian population, using data from
Methods and Materials
M AN U
2.
SC
Singaporean infants sampled longitudinally at multiple timepoints.
2.1. Participants
Infants were part of the Growing Up in Singapore Towards healthy Outcomes (GUSTO) study, which recruited 1247 pregnant women age 18 years or over from two major birthing
TE D
hospitals in Singapore, between November 2009 and May 2011. Detailed descriptions of the cohort have been reported previously [13]. We analyzed night sleep data from 893 infants (75.9% of all naturally conceived singleton deliveries) who provided data for at least one time
EP
point. Importantly, the 893 infants (75.9%) did differ in some demographic variables from the 259 infants (24.1%) with missing sleep data across all six time points. Similar to other cohort
AC C
studies [14], in our cohort, infants with sleep data more often had mothers who were older, of higher socio-economic backgrounds, and/or of Chinese origin than infants with missing sleep data.. Missing data analyses and sample characteristics of the current study can be found in the Online Supplement.
The GUSTO study was approved by the National Health Care Group Domain Specific 5
ACCEPTED MANUSCRIPT
Review Board and the SingHealth Centralized Institutional Review Board. Written, informed
RI PT
consent was obtained from all participants.
2.2. Sleep measures
Information about night sleep duration was obtained at age 3, 6, 9, 12, 18, and 24 months from caregiver reports on the revised Brief Infant Sleep Questionnaire (BISQ) [10,15], via the
M AN U
SC
question “How much time does your baby spend in sleep during the night?”
2.3. Statistical analysis
Latent growth curve analyses were run in Mplus version 7.3, using night sleep data from each infant at each time point to estimate the trajectory that represents the change in level of
TE D
night sleep across the period from 3 to 24 months. The maximum likelihood robust (MLR) estimator was used. Missing data was accounted for by full information maximum likelihood, which is robust to data missing at random and is recommended over complete case analysis [16].
EP
We established a trajectory of night sleep that was valid by modeling different latent growth curves and assessing them on a series of fit indices from simpler, more parsimonious models to
3.
AC C
more complex, less parsimonious ones.
Results
6
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9.5
8.5
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Hours of Night Sleep
9
8
7 3
6
9
12
15
18
24
M AN U
Age (Months)
SC
7.5
Fig. 1. Average night sleep trajectory from age 3 to 24 months with 95% confidence
TE D
intervals.
Figure 1 plots the trajectory from the best-fitting model, a piecewise latent growth curve that modeled an overall trajectory as the combination of two curves across all seven timepoints
EP
of sleep data. The first curvilinear curve was estimated across 3 to 12 months, with an average increase of 0.12 hour of sleep per month. The second curvilinear curve was estimated across 12
AC C
to 24 months, with an average increase of 0.02 hour of sleep per month. A χ2 test indicated that the rate of increase of night sleep in phase 2 was lower than in phase 1 (χ2 = 55.04, df = 1, p < 0.001). Nonetheless, the shape of the trajectories across both phases of sleep showed little variation (slope 1 variance = 0.01, SE = 0.01, p = 0.06; slope 2 variance = 0.00, SE = 0.00, p = 0.17) and were not related to each other (β = 0.16, SE = 0.41, p = 0.69) (see Online Supplement).
7
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4.
Discussion
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To the best of our knowledge, this is the first study to examine infant night sleep trajectories longitudinally within a Singaporean Asian sample. Our model shows that
Singaporean children followed a curvilinear increasing trajectory of sleep across infancy, marked
SC
by two latent slopes. The first slope, from age 3 to 12 months, indicated an increase of
approximately 0.12 hour of night sleep per month. The second slope, from age 12 to 24 months,
M AN U
also indicated a curvilinear increase, but at a slower rate of approximately 0.02 hour per month. The curvilinear pattern of increase for the first year is in agreement with previous studies in Caucasian samples that have investigated night sleep with trajectories [5,6] as well as crosssectional [4,7,9,17] analyses. However, the pattern of trajectory development from 12 to 24 months is different from that found previously in predominantly Caucasian samples in which
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infants exhibited either a decreasing trajectory [6] or a plateau in the night sleep trajectories [4,7]. Only one other cohort study reported an increase in night sleep from age 6 to 48 months
duration.
EP
[8]; however, this study explored continuous night sleep duration rather than total night sleep
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There is an overall increase in the night sleep trajectory in this Southeast Asian sample, which is indeed different from existing Western samples. This difference may be due to societal differences in bedtime routines [10], parental sleep-settling behaviors [18,19], and parental perception of sleep problems [20] that have been attributed to influencing night sleep duration [10,19,21], whereas the first year is driven more by biological factors such as brain maturation of circadian networks [22–24] and/or genetic factors [8,9]. Indeed, a twin study that explored sleep in infants at both 6 months and 18 months of age revealed that the proportion of night sleep 8
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duration in infancy at 6 months was driven mainly by genetic factors that are likely to be involved in brain development, whereas environmental factors played a larger role in
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determining proportion of night sleep duration at 18 months [9]. A limitation of this study is that we made use of a caregiver-reported questionnaire, which may be more susceptible to reporting biases. However, the BISQ has been validated
SC
against other, more objective measures such as sleep actigraphy [15]. Also, the means reported in our study are similar to those in a separate, larger-scale BISQ study that included data from
M AN U
Singaporean infants and toddlers [10]. These trajectories may also represent an upper bound estimate of sleep duration, as the infants in our study were from families with higher socioeconomic backgrounds [25].
Still, data from this study may be helpful in informing sleep medicine guidelines in
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Singapore and possibly other predominantly Asian countries on the average sleep trajectory within infants from age 3 to 24 months. It is especially useful for clinicians and health professionals to understand that “one-size-does-not-fit-all”; hence Western-based sleep-related
EP
guidelines and interventions may not always be applicable to infants from predominantly Asian countries, especially after the first year of age, where cross-cultural differences in sleep
5.
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trajectories are more likely to be present.
Conclusion
To the best of our knowledge, this is the first study exploring night sleep trajectories in an Asian cohort. Our findings indicate that night sleep trajectories among Singaporean infants initially follow a curvilinear increasing night sleep trajectory, similar to other predominantly 9
ACCEPTED MANUSCRIPT
Caucasian cohorts. However Singaporean infants continue to display a curvilinear increase (at a slower rate) in night sleep trajectories in the second year, instead of a decreasing trajectory or a stable-plateaued trajectory in other predominantly Caucasian samples. The differences in
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EP
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SC
infancy, while being more environmentally driven in late infancy.
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findings suggest that sleep may be less susceptible to environmental differences in in early
10
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Acknowledgements The GUSTO study group includes the following individuals: Allan Sheppard, Amutha
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Chinnadurai, Anne Eng Neo Goh, Anne Rifkin-Graboi, Anqi Qiu, Arijit Biswas, Bee Wah Lee, Birit F.P. Broekman, Boon Long Quah, Borys Shuter, Chai Kiat Chng, Cheryl Ngo, Choon Looi Bong, Christiani Jeyakumar Henry, Cornelia Yin Ing Chee, Yam Thiam Daniel Goh, Doris Fok,
SC
Fabian Yap, George Seow Heong Yeo, Helen Chen, Hugo P S van Bever, Iliana Magiati, Inez Bik Yun Wong, Ivy Yee-Man Lau, Jeevesh Kapur, Jenny L. Richmond, Jerry Kok Yen Chan,
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Joanna D. Holbrook, Joshua J. Gooley, Keith M. Godfrey, Kenneth Kwek, Kok Hian Tan, Krishnamoorthy Niduvaje, Leher Singh, Lin Lin Su, Lourdes Mary Daniel, Lynette Pei-Chi Shek, Marielle V. Fortier, Mark Hanson, Mary Foong-Fong Chong, Mary Rauff, Mei Chien Chua, Michael Meaney, Mya Thway Tint, Neerja Karnani, Ngee Lek, Oon Hoe Teoh, P. C. Wong, Peter D. Gluckman, Pratibha Agarwal, Rob M. van Dam, Salome A. Rebello, Seang-Mei
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Saw, Shang Chee Chong, Shirong Cai, Shu-E Soh, Sok Bee Lim, Chin-Ying Stephen Hsu, Victor Samuel Rajadurai, Walter Stunkel, Wee Meng Han, Wei Wei Pang, Yap-Seng Chong, Yin Bun
EP
Cheung, Yiong Huak Chan, and Yung Seng Lee. This research is supported by the Singapore National Research Foundation under its
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Translational and Clinical Research (TCR) Flagship Programme and administered by the Singapore Ministry of Health’s National Medical Research Council (NMRC), SingaporeNMRC/TCR/004-NUS/2008; NMRC/TCR/012-NUHS/2014. Additional funding is provided by the Singapore Institute for Clinical Sciences, Agency for Science Technology and Research (A*STAR), Singapore, NMRC (NMRC/CBRG/0039/2013), and Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2012-T2-2-130).
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[1]
Touchette E, Côté SM, Petit D, Liu X, Boivin M, Falissard B, et al. Short nighttime sleep-
Taveras EM, Rifas-Shiman SL, Oken E, Gunderson EP, Gillman MW. Short sleep
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duration and hyperactivity trajectories in early childhood. Pediatrics 2009;124:e985–93.
duration in infancy and risk of childhood overweight. Arch Pediatr Adolesc Med 2008;162:305. [4]
Teng A, Bartle A, Sadeh A, Mindell J. Infant and toddler sleep in Australia and New
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Zealand. J Paediatr Child Health 2012;48:268–73.
Bruni O, Baumgartner E, Sette S, Ancona M, Caso G, Di Cosimo ME, et al. Longitudinal study of sleep behavior in normal infants during the first year of life. J Clin Sleep Med
Iglowstein I, Jenni OG, Molinari L, Largo RH. Sleep duration from infancy to
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[6]
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2014;10:1119–27.
adolescence: Reference values and generational trends. Pediatrics 2003;111:302–7.
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Sadeh A, Mindell JA, Luedtke K, Wiegand B. Sleep and sleep ecology in the first 3 years: A Web-based study. J Sleep Res 2009;18:60–73.
[8]
Touchette E, Dionne G, Forget-Dubois N, Petit D, Pérusse D, Falissard B, et al. Genetic and environmental influences on daytime and nighttime sleep duration in early childhood.
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Pediatrics 2013;131:e1874–80. [9]
Dionne G, Touchette E, Forget-Dubois N, Petit D, Tremblay RE, Montplaisir JY, et al.
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Associations between sleep-wake consolidation and language development in early childhood: A longitudinal twin study. Sleep 2011;34:987–95. [10]
Mindell JA, Sadeh A, Wiegand B, How TH, Goh DYT. Cross-cultural differences in
Jenni OG, O’Connor BB. Children’s sleep: An interplay between culture and biology. Pediatrics 2005;115:204–16.
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infant and toddler sleep. Sleep Med 2010;11:274–80.
Liu X, Liu L, Owens JA, Kaplan DL. Sleep patterns and sleep problems among schoolchildren in the United States and China. Pediatrics 2005;115:241–9. Soh S-E, Tint MT, Gluckman PD, Godfrey KM, Rifkin-Graboi A, Chan YH, et al. Cohort
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profile: Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort study. Int J Epidemiol 2013. doi:10.1093/ije/dyt125. Fraser A, Macdonald-Wallis C, Tilling K, Boyd A, Golding J, Davey Smith G, et al.
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Cohort profile: The Avon Longitudinal Study of Parents and Children: ALSPAC mothers
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cohort. Int J Epidemiol 2013;42:97–110.
Sadeh A. A Brief screening questionnaire for infant sleep problems: Validation and
findings for an Internet sample. Pediatrics 2004;113:e570–7.
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Enders CK. Dealing with missing data in developmental research. Child Dev Perspect 2013;7:27–31.
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[17]
Burnham MM, Goodlin-Jones BL, Gaylor EE, Anders TF. Nighttime sleep-wake patterns and self-soothing from birth to one year of age: A longitudinal intervention study. J Child
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Mindell JA, Sadeh A, Kwon R, Goh DYT. Cross-cultural differences in the sleep of preschool children. Sleep Med 2013;14:1283–9.
Mindell JA, Sadeh A, Kohyama J, How TH. Parental behaviors and sleep outcomes in
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Psychol Psychiatry 2002;43:713–25.
infants and toddlers: A cross-cultural comparison. Sleep Med 2010;11:393–9. Sadeh A, Mindell J, Rivera L. “ My child has a sleep problem”: A cross-cultural
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[20]
comparison of parental definitions. Sleep Med 2011;12:478–82. [21]
Price AMH, Brown JE, Bittman M, Wake M, Quach J, Hiscock H. Children’s sleep
2014;99:119–25. [22]
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patterns from 0 to 9 years: Australian population longitudinal study. Arch Dis Child
Jenni OG, Borbély AA, Achermann P. Development of the nocturnal sleep
[23]
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electroencephalogram in human infants. 2004;286. Mirmiran M, Maas YG., Ariagno RL. Development of fetal and neonatal sleep and
[24]
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circadian rhythms. Sleep Med Rev 2003;7:321–34.
Dahl RE. The regulation of sleep and arousal: Development and psychopathology. Dev
Psychopathol 1996;8:3.
[25]
Biggs SN, Lushington K, James Martin A, van den Heuvel C, Declan Kennedy J. Gender, socioeconomic, and ethnic differences in sleep patterns in school-aged children. Sleep Med 2013;14:1304–9. 14
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Highlights •
This is the first longitudinal study exploring infant night sleep trajectories in Asian
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infants. Analyses revealed a trajectory modeled by two freely estimated latent growth curves.
•
The first phase (3−12 months) displayed a curvilinear increase in night sleep duration.
•
The second phase (12−24 months) displayed a curvilinear increase but at a slower rate.
AC C
EP
TE D
M AN U
SC
•
S1389-9457(17)30048-5
DOI:
10.1016/j.sleep.2017.01.013
Reference:
SLEEP 3300
To appear in:
Sleep Medicine
Received Date: 1 October 2016 Revised Date:
19 January 2017
Accepted Date: 22 January 2017
Please cite this article as: Goh SKY, Tham EK, Goh DY, Hoe TO, Saw SM, Yap F, Chong Y-S, Qiu A, Broekman BF, Infant night sleep trajectory from age 3 to 24 months: Evidence from the Singapore GUSTO study, Sleep Medicine (2017), doi: 10.1016/j.sleep.2017.01.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Infant night sleep trajectory from age 3 to 24 months: Evidence from the Singapore
RI PT
GUSTO study
Shaun K.Y. Goha, Elaine KH Thamb, Daniel YT Gohc, Teoh Oon Hoed, Seang Mei Sawe, Fabian
Department of Bioengineering and Clinical Imaging Research Center, National University of
M AN U
a
SC
Yapd, Yap-Seng Chongb,f, Anqi Qiua,b, Birit FP Broekmanb,*
Singapore, Singapore b
Singapore Institute for Clinical Sciences, Agency for Science and Technology Research
(A*STAR), Brenner Centre for Molecular Medicine, Singapore
Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore,
TE D
c
National University Health System, Singapore
KK Women’s and Children’s Hospital, Singapore
e
Saw Swee Hock School of Public Health, National University of Singapore, Singapore
f
Department of Obstetrics & Gynaecology, Yong Loo Lin School of Medicine, National
AC C
EP
d
University of Singapore, National University Health System, Singapore
S.K.Y.G. and E.K.H.T. contributed equally to this work
1
ACCEPTED MANUSCRIPT
ARTICLE INFO Article history:
RI PT
Received Received in revised form
SC
Accepted
M AN U
Keywords: Infant sleep
Latent growth curves
TE D
Trajectory
EP
*Corresponding author at: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Brenner Centre for Molecular Medicine, 30 Medical
AC C
Drive, Singapore 117609, Singapore. Tel.: 0065 90095444; fax: 0065 6776 6840. E-mail address: [email protected] (B.F.P. Broekman)
2
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ABSTRACT Objective: Longitudinal studies on night sleep trajectories throughout infancy are sparse.
RI PT
Moreover, most studies have examined samples in Caucasian individuals, although cultural differences in sleep habits have been described. To expand on the current literature, we aimed to determine night sleep trajectories in an Asian population from age 3 to 24 months.
SC
Methods: Night sleep duration from a subset of 893 infants within the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort study was determined using the caregiver-
M AN U
reported Brief Infant Sleep Questionnaire. Latent growth curves were used to analyze sleep trajectories at 3, 6, 9, 12, 18, and 24 months.
Results: The overall trajectory was modeled with a piecewise model with two freely estimated curves. In the first phase (age 3−12 months), infants displayed an average curvilinear increase in
TE D
night sleep trajectories of 0.12 hour per month. In the second phase (age 12−24 months), infants continued to display a curvilinear increase, but at a slower average rate of 0.02 hour per month. Conclusions: The sleep trajectory of Singaporean infants appeared similar to other
EP
predominantly Caucasian cohorts for 3−12 months but not for 12−24 months, in which infants
AC C
from predominantly Caucasian cohorts mostly displayed a decreasing or a stable-plateaued trajectory. This is in concordance with existing studies that suggest that the underlying influences of night sleep shift from predominantly biological influences to increasing environmental influences with age.
3
ACCEPTED MANUSCRIPT
1.
Introduction
RI PT
Infant night sleep duration is known to be important to subsequent developmental and health outcomes such as cognitive and motor development [1], behavioural problems [2], and obesity risk [3]. However, unlike day sleep duration [4–7], development of night sleep duration
SC
throughout infancy is not well known.
First of all, studies on night sleep duration in infancy are sparse [4,6–8]. Aside from large
M AN U
cross-sectional studies that report increases in night sleep across the first year [4,7], to date there have been only two longitudinal studies that explicitly report night sleep longitudinally beyond the first year of infancy. The Zurich Longitudinal Studies reported that night sleep trajectories, after an increase in the first year of life, showed a subsequent curvilinear decrease until
TE D
adolescence [6]. However, the Quebec Newborn Twin Study reported a curvilinear increase in sleep from 6 to 48 months [8,9]. In summary, although few in number, existing studies suggest an overall increase in the level of night sleep until 1 year of age, but are less consistent in their
EP
findings after the first year.
AC C
Moreover, these findings are mainly from predominantly Caucasian samples, although previous cross-cultural studies [10–12] found differences of large effect size in night sleep duration among predominantly Caucasian samples compared to predominantly Asian samples [10]. Hence, it remains unclear how the level of night sleep develops within individuals across infancy and whether existing published trajectories are applicable to non-Caucasian samples. Infant night sleep plays a role in a range of health and developmental outcomes [1–3]. Interestingly, cross-sectional data have revealed differences in night sleep duration between 4
ACCEPTED MANUSCRIPT
predominantly Caucasian and predominantly Asian populations [10]. Hence, understanding the longitudinal developmental trajectory patterns of sleep among infants of different cultural backgrounds is important to inform clinicians and (local) clinical guidelines in sleep medicine,
RI PT
including possible cultural differences in these. Here we expand on the existing knowledge to understand the trajectory of infant night sleep in an Asian population, using data from
Methods and Materials
M AN U
2.
SC
Singaporean infants sampled longitudinally at multiple timepoints.
2.1. Participants
Infants were part of the Growing Up in Singapore Towards healthy Outcomes (GUSTO) study, which recruited 1247 pregnant women age 18 years or over from two major birthing
TE D
hospitals in Singapore, between November 2009 and May 2011. Detailed descriptions of the cohort have been reported previously [13]. We analyzed night sleep data from 893 infants (75.9% of all naturally conceived singleton deliveries) who provided data for at least one time
EP
point. Importantly, the 893 infants (75.9%) did differ in some demographic variables from the 259 infants (24.1%) with missing sleep data across all six time points. Similar to other cohort
AC C
studies [14], in our cohort, infants with sleep data more often had mothers who were older, of higher socio-economic backgrounds, and/or of Chinese origin than infants with missing sleep data.. Missing data analyses and sample characteristics of the current study can be found in the Online Supplement.
The GUSTO study was approved by the National Health Care Group Domain Specific 5
ACCEPTED MANUSCRIPT
Review Board and the SingHealth Centralized Institutional Review Board. Written, informed
RI PT
consent was obtained from all participants.
2.2. Sleep measures
Information about night sleep duration was obtained at age 3, 6, 9, 12, 18, and 24 months from caregiver reports on the revised Brief Infant Sleep Questionnaire (BISQ) [10,15], via the
M AN U
SC
question “How much time does your baby spend in sleep during the night?”
2.3. Statistical analysis
Latent growth curve analyses were run in Mplus version 7.3, using night sleep data from each infant at each time point to estimate the trajectory that represents the change in level of
TE D
night sleep across the period from 3 to 24 months. The maximum likelihood robust (MLR) estimator was used. Missing data was accounted for by full information maximum likelihood, which is robust to data missing at random and is recommended over complete case analysis [16].
EP
We established a trajectory of night sleep that was valid by modeling different latent growth curves and assessing them on a series of fit indices from simpler, more parsimonious models to
3.
AC C
more complex, less parsimonious ones.
Results
6
ACCEPTED MANUSCRIPT
9.5
8.5
RI PT
Hours of Night Sleep
9
8
7 3
6
9
12
15
18
24
M AN U
Age (Months)
SC
7.5
Fig. 1. Average night sleep trajectory from age 3 to 24 months with 95% confidence
TE D
intervals.
Figure 1 plots the trajectory from the best-fitting model, a piecewise latent growth curve that modeled an overall trajectory as the combination of two curves across all seven timepoints
EP
of sleep data. The first curvilinear curve was estimated across 3 to 12 months, with an average increase of 0.12 hour of sleep per month. The second curvilinear curve was estimated across 12
AC C
to 24 months, with an average increase of 0.02 hour of sleep per month. A χ2 test indicated that the rate of increase of night sleep in phase 2 was lower than in phase 1 (χ2 = 55.04, df = 1, p < 0.001). Nonetheless, the shape of the trajectories across both phases of sleep showed little variation (slope 1 variance = 0.01, SE = 0.01, p = 0.06; slope 2 variance = 0.00, SE = 0.00, p = 0.17) and were not related to each other (β = 0.16, SE = 0.41, p = 0.69) (see Online Supplement).
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4.
Discussion
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To the best of our knowledge, this is the first study to examine infant night sleep trajectories longitudinally within a Singaporean Asian sample. Our model shows that
Singaporean children followed a curvilinear increasing trajectory of sleep across infancy, marked
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by two latent slopes. The first slope, from age 3 to 12 months, indicated an increase of
approximately 0.12 hour of night sleep per month. The second slope, from age 12 to 24 months,
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also indicated a curvilinear increase, but at a slower rate of approximately 0.02 hour per month. The curvilinear pattern of increase for the first year is in agreement with previous studies in Caucasian samples that have investigated night sleep with trajectories [5,6] as well as crosssectional [4,7,9,17] analyses. However, the pattern of trajectory development from 12 to 24 months is different from that found previously in predominantly Caucasian samples in which
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infants exhibited either a decreasing trajectory [6] or a plateau in the night sleep trajectories [4,7]. Only one other cohort study reported an increase in night sleep from age 6 to 48 months
duration.
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[8]; however, this study explored continuous night sleep duration rather than total night sleep
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There is an overall increase in the night sleep trajectory in this Southeast Asian sample, which is indeed different from existing Western samples. This difference may be due to societal differences in bedtime routines [10], parental sleep-settling behaviors [18,19], and parental perception of sleep problems [20] that have been attributed to influencing night sleep duration [10,19,21], whereas the first year is driven more by biological factors such as brain maturation of circadian networks [22–24] and/or genetic factors [8,9]. Indeed, a twin study that explored sleep in infants at both 6 months and 18 months of age revealed that the proportion of night sleep 8
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duration in infancy at 6 months was driven mainly by genetic factors that are likely to be involved in brain development, whereas environmental factors played a larger role in
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determining proportion of night sleep duration at 18 months [9]. A limitation of this study is that we made use of a caregiver-reported questionnaire, which may be more susceptible to reporting biases. However, the BISQ has been validated
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against other, more objective measures such as sleep actigraphy [15]. Also, the means reported in our study are similar to those in a separate, larger-scale BISQ study that included data from
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Singaporean infants and toddlers [10]. These trajectories may also represent an upper bound estimate of sleep duration, as the infants in our study were from families with higher socioeconomic backgrounds [25].
Still, data from this study may be helpful in informing sleep medicine guidelines in
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Singapore and possibly other predominantly Asian countries on the average sleep trajectory within infants from age 3 to 24 months. It is especially useful for clinicians and health professionals to understand that “one-size-does-not-fit-all”; hence Western-based sleep-related
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guidelines and interventions may not always be applicable to infants from predominantly Asian countries, especially after the first year of age, where cross-cultural differences in sleep
5.
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trajectories are more likely to be present.
Conclusion
To the best of our knowledge, this is the first study exploring night sleep trajectories in an Asian cohort. Our findings indicate that night sleep trajectories among Singaporean infants initially follow a curvilinear increasing night sleep trajectory, similar to other predominantly 9
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Caucasian cohorts. However Singaporean infants continue to display a curvilinear increase (at a slower rate) in night sleep trajectories in the second year, instead of a decreasing trajectory or a stable-plateaued trajectory in other predominantly Caucasian samples. The differences in
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infancy, while being more environmentally driven in late infancy.
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findings suggest that sleep may be less susceptible to environmental differences in in early
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Acknowledgements The GUSTO study group includes the following individuals: Allan Sheppard, Amutha
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Chinnadurai, Anne Eng Neo Goh, Anne Rifkin-Graboi, Anqi Qiu, Arijit Biswas, Bee Wah Lee, Birit F.P. Broekman, Boon Long Quah, Borys Shuter, Chai Kiat Chng, Cheryl Ngo, Choon Looi Bong, Christiani Jeyakumar Henry, Cornelia Yin Ing Chee, Yam Thiam Daniel Goh, Doris Fok,
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Fabian Yap, George Seow Heong Yeo, Helen Chen, Hugo P S van Bever, Iliana Magiati, Inez Bik Yun Wong, Ivy Yee-Man Lau, Jeevesh Kapur, Jenny L. Richmond, Jerry Kok Yen Chan,
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Joanna D. Holbrook, Joshua J. Gooley, Keith M. Godfrey, Kenneth Kwek, Kok Hian Tan, Krishnamoorthy Niduvaje, Leher Singh, Lin Lin Su, Lourdes Mary Daniel, Lynette Pei-Chi Shek, Marielle V. Fortier, Mark Hanson, Mary Foong-Fong Chong, Mary Rauff, Mei Chien Chua, Michael Meaney, Mya Thway Tint, Neerja Karnani, Ngee Lek, Oon Hoe Teoh, P. C. Wong, Peter D. Gluckman, Pratibha Agarwal, Rob M. van Dam, Salome A. Rebello, Seang-Mei
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Saw, Shang Chee Chong, Shirong Cai, Shu-E Soh, Sok Bee Lim, Chin-Ying Stephen Hsu, Victor Samuel Rajadurai, Walter Stunkel, Wee Meng Han, Wei Wei Pang, Yap-Seng Chong, Yin Bun
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Cheung, Yiong Huak Chan, and Yung Seng Lee. This research is supported by the Singapore National Research Foundation under its
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Translational and Clinical Research (TCR) Flagship Programme and administered by the Singapore Ministry of Health’s National Medical Research Council (NMRC), SingaporeNMRC/TCR/004-NUS/2008; NMRC/TCR/012-NUHS/2014. Additional funding is provided by the Singapore Institute for Clinical Sciences, Agency for Science Technology and Research (A*STAR), Singapore, NMRC (NMRC/CBRG/0039/2013), and Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2012-T2-2-130).
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Highlights •
This is the first longitudinal study exploring infant night sleep trajectories in Asian
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infants. Analyses revealed a trajectory modeled by two freely estimated latent growth curves.
•
The first phase (3−12 months) displayed a curvilinear increase in night sleep duration.
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The second phase (12−24 months) displayed a curvilinear increase but at a slower rate.
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•