Breastfeeding at night

Why do babies feed during the night?

There are many reasons for normal babies needing to feed at night. Three possible ones are: (1) breast milk and infant formula are relatively low in energy requiring babies to feed often, (2) the growing brain needs a lot of glucose which babies need to replenish frequently, and (3) babies are born very immature and require contact with parents, day and night. In short, human biology doesn’t support a pattern of sleeping through the night early in life.

A) Describing why babies need to feed at night and the role of breastfeeding

It is not fully understood why babies need to wake and feed during the night, but it may be because:

  1. Human milk is relatively low in energy.
  2. The human brain needs lots of glucose to work.
  3. Babies are born very immature.

In short, it is unreasonable to expect a baby to sleep through the night because our biology doesn’t support this pattern.

Breastfeeding has a role in infant sleep. Breastfeeding can help a baby fall asleep, thus limiting the length of the night waking. Some breast milk components will increase and decrease at various times during the day and night. These variations may be providing nutrients when they are most needed by the baby and also teaching and supporting the baby’s internal clock. For these reasons, breast milk can be called chrononutrition.

B) Human milk is relatively low in energy

An armadillo. Photo by Joe Lemm on Unsplash

Mammals are named for the Latin word for breast. Milk secretion may have started as early as 300 million years ago (Oftedal 2012). Now, there are about 4000 species of mammals today that inhabit a wide range of environments (McClellan 2008). Each type of mammal produces a distinctive type of milk to meet the needs of its young. The range in milk types is actually astonishing.

1) The hooded seal

Marine mammals such as whales, seals, and sea lions have milk that is high in fat. For example, hooded seal milk is 60 to 70% fat. By comparison, human milk is about 4% fat. Hooded seal mothers only breastfeed their pups for about one week. During this time, the pup gains 7 kilograms (15 pounds) to double its birth weight at the time of weaning (Oftedal 1988). The high fat content helps the pup gain weight quickly to keep warm, allowing it to leave the Arctic ice and enter the sea, safe from unstable sea ice and polar bears (Boyd 1998).

2) The Malaysian tree shrew

The Malaysian tree shrew produces milk with a fat content of about 25%, so the mother needs to spend only about two minutes with her young every other day to provide them with enough calories (Hubrecht 2010). As a result, she is less likely to give away the location of her young to predators, and can spend more time foraging for food.

3) Armadillos

Armadillos are mammals found in the south central U.S.A. and Central and South America. Their bodies are covered with bony plates. Their milk is very high in protein (8-11%) compared to the milk of other mammals. Human milk, by comparison, is only about 1.5% protein (Power 2018). The protein serves as a vehicle for calcium and phosphorus, which are needed to build the young armadillos’ armour.

4) Human milk

Human milk has relatively little fat, about four per cent, and its energy content is lower, like the milk of many land-based mammals. Yet, even compared with other land mammals, our babies grow slowly. They don’t need extra rich milk.

Because the baby’s stomach can take in only a small amount of this relatively low-energy milk, babies need to feed regularly to get enough nutrients to grow. If they slept through the night, they would go one-third of a 24-hour period without food. This is a long time, given the low energy of human milk.

Infant formula is similar in calories to human milk.

C) The human brain needs a lot of milk sugar to work

Human milk has a lot of milk sugar (lactose) and fewer nutrients compared with the milk of other non-primate mammals (Sellen 2007). The baby’s body turns lactose into glucose, which is then used by the brain for energy.

The human brain is large and complicated compared with the brains of other mammals our size (Cairo 2011). It accounts for only 2% of an adult’s weight but consumes 20% of all the energy our bodies use (Mergentahler 2013). A baby’s brain is about 10% of its body weight but uses a remarkable 50% of the energy used (Grande Covián 1979).

The human brain grows quickly during the first year, tripling its weight from about 300 grams (10 ounces) to about 900 gm (30 oz) (Dekaban 1978). The average adult brain weighs 1,300 to 1,400 gm (around 3 lbs). 

In the first year of life, while the brain triples in size, the average baby’s height increases only by half, from about 50 centimetres (20 inches) to 75 cm (30 in).

Given the large size of the human brain, its high energy demands, and its rapid growth during the first year, it’s most likely that babies wake up to feed at night to get the glucose necessary for their brains to work and grow.

D) Babies are born immature

Compared with the young of other species, human babies are extremely immature at birth and take a long time to mature. Indeed, our brains are not truly mature until we are 25 years of age (Arain 2013).

As a result, human babies need close contact with their parents over a long period. Unlike other mammals, human babies can’t walk, can’t feed themselves, can’t keep themselves warm, and so on. This is true during the night as well as the day, so many babies won’t sleep through the night.  

A lack of contact and the stress caused by separation can have long-term health consequences.

E) Other reasons for waking

Babies may also wake up other reasons such as painful tummy cramps as they digest milk, feeling too warm or cold, needing a diaper change, or unfamiliar sounds. 

References

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Cairo O. External measures of cognition. Front. Hum. Neurosci. 2011; Oct 4
 
Dekaban A.S. Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights. Ann. Neurology,1978;4:345-356
 
Grande Covián F. [Energy metabolism of the brain in children (author's transl)]. [Article in Spanish] An Esp Pediatr. 1979 Mar;12(3):235-44
 
Hubrecht, RC, Kirkwood J. The UFAW Handbook on the Care and Management of Laboratory and Other Research Animals. 8th Ed. John Wiley & Sons 2010
  
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Oftedal OT, Doness DJ, Bowen WD. The composition of hooded seal (Cystophora cristata) milk: an adaptation for postnatal fattening. Canadian Journal of Zoology, 1988; 66(2): 318-322
 
Power ML, Watts MS, Murtough K, et al. Macronutrient composition of milk of captive nine-banded armadillos (Dasypus novemcinctus). J Mammology 2018;99(2):498-504