Breastfeeding and sleep

A human baby is born "premature" compared to many mammals. Why? Because otherwise it would be unable to leave the uterus and pass through the birth canal. At birth, its brain is only a quarter of its adult size [4]!

A baby is born before its head becomes too large to pass through. And it is born with a very tiny stomach. At birth, it can hold only 5 to 7 ml of liquid (barely a teaspoonful!). That is why just a few drops of colostrum are exactly what it needs at birth.

Yet it needs a continuous source of fuel to nourish its brain, which will grow a great deal in the first few months. So it needs frequent feeds.

That is why giving a "large" bottle to settle a baby will serve no purpose other than to give it a stomachache and cause even more frequent wakings. Imagine being given several litres of soup just before going to sleep!

At birth, the sleep cycles of babies' sleep are much shorter than in adults: 50 minutes compared to 90 minutes. 

And each time they transition between cycles, they may wake up. During the first months, or even the first years, sleep is still fragile and poorly structured.

Before 3 months, a baby has no circadian organisation. Research has shown that the beginnings of circadian organisation do not start to develop until 8 weeks after birth[5]. 

After 3 months, the influence of day and night increases and sleep periods lengthen during the night. However, circadian organisation is not complete until 1 year[6] or even 2 years, depending on the research. 

It is worth noting that at 9 months, the proportion of children who start waking again at night increases, reaching a peak in the second year. At 3 years old, 20 to 35% of children still wake during the night, and this decreases until the age of 5[7].

Melatonin, the levels of which increase in your milk at night (melatonin is undetectable in daytime milk[8]), will help your baby regulate their natural clock[9].

In addition to melatonin, breast milk produced at night is rich in other substances such as tryptophan, an amino acid that induces sleep. It is a precursor to serotonin, a hormone essential for the brain and its development. Serotonin helps the brain to function better, has a positive effect on mood, and helps to organise sleep/wake cycles. Tryptophan will increase the number of serotonin receptors. A baby breastfed at night will therefore develop more serotonin receptors, as shown by Darcia Narvaez, an American researcher[10]. 

A study on newborns showed that having the baby in the mother's room significantly improved the baby's sleep (33% peaceful sleep compared with 25% for those placed in a nursery) and wellbeing (crying period 0.6% compared with 7.5%), without reducing the mothers' sleep comparatively[11].

When breastfeeding, you may feel tired — this is normal. It is a release that occurs at the moment of putting the baby to the breast, with a sensation of thirst in the first few weeks.

The exact reasons for this mechanism are not well understood (dopamine release promoted by prolactin and/or oxytocin, which can also act directly on brain receptors and has an anxiolytic and sedative effect) [12] [13].

Prolactin accelerates the transition to slow-wave sleep, and therefore to recovery. Sleep will thus be of better quality, even if much more fragmented, with more frequent waking.

Prolactin is a hormone that establishes, builds, and maintains lactation. And like melatonin, it also follows the circadian rhythm. In the first days of breastfeeding, the body sets up prolactin receptors in the breasts to regulate milk production. With each feed, prolactin levels rise. 

Furthermore, breastfeeding at night helps to prevent engorgement, and the drop in milk production that can result from it [14].

For mothers with low breast storage capacity, there cannot be prolonged intervals between feeds — and this applies equally during the day and at night [15]. Finally, night feeds are most often necessary to maintain lactation with a certain number of feeds in 24 hours. To find out more about this, see our article on how to increase milk supply. 

A study conducted with 204 exclusively breastfeeding mothers examined the relationship between room-sharing or not, the number of feeds, and infant weight gain. Among newborns who stayed with their mother and were fed on demand, weight gain was greater, despite a lower volume of milk consumed compared to those fed with formula. The authors explain this difference by the fact that mother-baby contact led to less agitation and crying, and therefore less energy expended [16].

Infant colic, for which there is no known "cure", is a phenomenon affecting babies between 2 weeks and 4 months of age, characterised by episodes of intense crying, usually in the evening.

Indeed, whilst melatonin does not follow the circadian rhythm at this age, another hormone, serotonin, does. Melatonin and serotonin work in tandem, normally balancing each other out. Serotonin reaches its peak during the night, and when there is no melatonin to counterbalance it, it can cause intestinal contractions. Melatonin relaxes the intestinal muscles, thereby reducing the risk of colic, but babies do not produce it on their own before the age of 3 months. 

Thus, breastfeeding, by providing an external source of melatonin, can help reduce the risk of colic [17] [18].

Sudden infant death syndrome may be explained in part by a reduced ability to rouse from sleep. Night-time awakenings may therefore be a protective factor. Indeed, a baby that wakes (briefly) during the night will tend to spend more time in lighter, more protective sleep phases.

Breastfed babies tend to wake more frequently, rousing for a few minutes to feed. The National Health and Medical Research Council in Australia suggests that breastfeeding may reduce the risk of sudden infant death syndrome by 44%[19].

An American researcher studied the sleep of breastfed babies who shared their mother's bed. These babies spent more time in sleep phases 1 and 2 (lighter and therefore more protective), had fewer episodes of obstructive apnoea, and had more regular breathing than babies who slept alone in their own room[20].

According to American researcher McKenna, breastfeeding saves around 750 babies each year, whether from sudden infant death syndrome (SIDS) or other illnesses[21].

An analysis of 288 studies found evidence that breastfeeding may protect against SIDS, and that this protection was stronger when breastfeeding was exclusive[22]. 

Another analysis from 1983 examined newborn/mother statistics, looking in particular at the intensity and duration of breastfeeding. It found a small protective effect of breastfeeding against SIDS, which increased the more extensive (exclusive) and prolonged the breastfeeding was[23].

Between one and four months, babies begin to consolidate their sleep[27], converting their short sleep phases into longer periods of rest. The mother's rhythm helps the baby find its own.

By around three months, approximately two thirds of babies have begun to consolidate their sleep, even though half of them subsequently regress[28].

At one year old, around 50% of babies still need to be soothed by their parents at least once a night on almost every night[29].