Why is sleep so important to babies?

By Cai Shirong

Sleep-deprived parents will resort to trawling the internet, reading every single self-help book or signing up for some online sleep training programme – anything to improve their babies’ sleep (and in turn their own). If you've read enough, you will realise that sleep advice for infants can sometimes be contradicting, confusing or impractical.

My personal “favourite” tip? “Put the baby to bed awake but drowsy. Recognise those sleep cues and make a dash for the cot!” Jokes aside, sleep (or the lack thereof) impacts our little ones in more ways than one.

The importance of slumber
Babies are born with no established circadian rhythm and it will be developed only when they are about three to four months old. This explains why your child may sleep in the day and not at night (much to your despair). Parents can help this process by exposing babies to natural light cues in the day, and similarly provide a dark environment at night. This helps junior to distinguish day (light) from night (dark).

Sleep in the first year of life is imperative as it is an important period for maturation of sleep, with consolidation of nocturnal sleep and decrease in day sleep duration. Infant sleep plays an important role in a child’s development, including cognition and physical growth – it’s associated with overall cognitive development, as well as specific cognitive functions such as memory, language and executive function. Sufficient and quality sleep may favour optimal cognitive function in children because it helps with brain maturation and memory consolidation. Slow wave sleep – often referred to as deep sleep – plays an important role in memory consolidation, which may be important during early language acquisition.

Growth hormone is also released during slow wave sleep, contributing to gain in body length. Short sleep duration in infants have been reported to be linked to adiposity and obesity later in life.^1,2 Sleep deprivation is associated with increased ghrelin (hunger hormone) and decreased leptin (satiety hormone), resulting in increased caloric intake leading to adiposity.

How much sleep do babies need?
The National Sleep Foundation (NSF) recommends a total sleep duration of 14 to 17 hours a day from birth to three months; 12 to 15 hours a day from four to 11 months; and 11 to 14 hours a day for infants aged one to two years. Sleep problems during infancy have been shown to be associated with subsequent sleep problems during early childhood, which in turn are linked to behavioural and learning problems.

Cultural differences in sleep during infancy
Short sleep duration is prevalent in Asian countries, not just among adults, but also among infants. A cross-cultural study³ conducted across 11 Asian countries (China, Hong Kong, India, Indonesia, Japan, Korea, Singapore, Malaysia, Philippines, Taiwan, Thailand, and Vietnam) including Singapore and five Caucasian countries (Australia, Canada, New Zealand, United Kingdom, and United States) found that infants (aged zero to 36 months) from Asian countries had shorter sleep duration and later bedtimes compared to their Caucasian counterparts.

Bedtimes ranged from as early as 1927 hours in New Zealand to 2217 hours in Hong Kong, while total sleep duration ranged from 11.6 hours in Japan to 13.3 hours in New Zealand. Interestingly, there are no significant differences in the day sleep duration across the countries. There are also differences in sleep-related parenting practices. For example, Asian parents are more likely to bed-share and room-share as compared to Caucasian parents. Bed-sharing was practised in 5.8 percent and 83.2 percent of the participants surveyed from New Zealand and Vietnam respectively. It is not entirely clear if the driving forces behind the cultural differences in sleep are biological and/or environmental.

Factors that affect sleep in young children
Aside from cultural influence, many other factors can affect sleep in young children, including biological, environmental and social factors. These include socioeconomic status, gender, maternal age and education, screen time, sleeping arrangement and diet/nutrition.^4,5 Ironically, there is no magic bullet that’s guaranteed to make babies “sleep like a baby”.

Better sleep for baby
In general, sleep hygiene is important in improving the sleep of little ones (or even the not so little ones like us!). Sleep hygiene refers to good sleep habits and not how clean your baby or the bedsheets are – although those are good to have too! And this is especially true for infants who need consistency and routine in order to get good sleep. This includes keeping to the same bedtime every day and having some form of bedtime routine. Infants, as we come to realise, are really creatures of habit. Having bedtime and playtime routines also helps them to regulate hormone production and secretion.

Risk factors that influence sleep in early infancy are not as well-studied as those in school-going children. However, investigating early determinants of sleep may help us to better understand physiopathology as well as develop prevention interventions of unhealthy sleep patterns from an early age.

References

1. Tham EK, Schneider N, Broekman BF. Infant sleep and its relation with cognition and growth: a narrative review. Nature and science of sleep. 2017; 9: 135-149.
2. Zhou Y, Aris IM, Tan SS, et al. Sleep duration and growth outcomes across the first two years of life in the GUSTO study. Sleep medicine. 2015; 16 (10): 1281-1286.
3. Mindell JA, Sadeh A, Wiegand B, How TH, Goh DY. Cross-cultural differences in infant and toddler sleep. Sleep medicine. 2010; 11 (3): 274-280.
4. Plancoulaine S, Reynaud E, Forhan A, et al. Night sleep duration trajectories and associated factors among preschool children from the EDEN cohort. Sleep medicine. 2018; 48: 194-201.
5. Touchette E, Cote SM, Petit D, et al. Short nighttime sleep-duration and hyperactivity trajectories in early childhood. Pediatrics. 2009; 124 (5): e985-993.
   

ABOUT THE AUTHOR
_{Dr Cai Shirong’s main research interest is in infant sleep as a modifiable target for health interventions and the risk factors that shape infant sleep. Presented with the opportunities to access developmental cohorts strategically positions Dr Cai to study infant sleep alongside subsequent developmental stage outcomes such as cognition, mood, behaviours, growth, adiposity and cardio-metabolic health. Aside from infant sleep, she also has a keen interest in multidisciplinary research, linking psychology and neuroscience with metabolic conditions such as gestational diabetes.}