Why do babies need TONS of sleep

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Okay so this has always perplexed me. It’s not so much a question of why babies need sleep. I understand why everyone needs sleep. Put simply, their bodies grow and repair themselves. However, I’ve been told by many parents that they put their babies to bed at 7:00PM and they are supposed to sleep until around 7:00AM. What I have found, however, is that most of the same parents also complain that their babies are waking up waaay too early. My roommates, specifically, have been dealing with their baby waking up at 4:30AM very consistently.

I have studied the mechanics of sleep (cycles, stages, conditions, etc) on account of my narcolepsy. The science doesn’t add up here, but I am certainly not a pediatrician. To compound the issue, they also put their babies down for naps that are often a couple hours long. Wouldn’t this be counter-intuitive? Babies should have a circadian rhythm, and their bodies should naturally know when they are ready to be awake. Is this really the correct course of action for a baby? Why do babies need so much sleep?

In: Biology

12 Answers

Anonymous 0 Comments

Babies *triple* their weight by their 1st birthday. Additionally there is a ton of brain development that happens in the first couple years of life. The brain doubles in size in the 1st year of life. This large amount of growth takes a lot of energy so they conserve energy in other ways, namely sleep.


Just because you mentioned it, the circadian rhythm doesn’t really develop until 2-3 months of age. Before that hunger is going to be the main sleep-wake driver.

Anonymous 0 Comments

Babies don’t actually develop a circadian rhythm for the first few months. In general, growth and development takes a lot of energy and sleep conserves energy and is especially important for cognitive development, which babies are doing a lot of. The lack of circadian rhythm can exacerbate this, as they have shorter sleep cycles.

Anonymous 0 Comments

I think you’re missing a few things, both on the practicalities of infants but also the reasons for sleep.

As a practical matter, if you put your baby to bed later, what you get is a crankier baby at 4:30am (or 5am, or 6am). This is annoying as hell, yes. It’s also pretty reliable.

Similarly, if you skip naps, you get “overtired” babies, not ones that sleep better.

Why: Well babies *are not adults* or even older children, and the sleep cycle mechanics you studied don’t necessarily apply to them as neatly. They don’t *have* an established circadian rhythm like adults or older kids do.

As for “why do they need so much sleep,” you actually already answered this: “bodies grow and repair themselves.” Babies are growing a *lot more* than older children or especially adults. So they need a ton more sleep. Don’t ask why babies sleep so much, ask why they’d *ever* wake up. They wake up to eat more, and/or to communicate other issues (mainly by crying). Then they go back to sleep to use all that food to grow. Before too long they start sleeping less and spending more time awake so they can learn more, but little kids still sleep a *lot* more than adults – 10-12 hours compared to the adult 8-ish. Again, this is because they’re growing, and that happens asleep.

Basically, they sleep a lot because they’re growing a lot, and they wake up at annoying random times because their bodies don’t have an established sleep cycle.

Anonymous 0 Comments

Babies do communicate very loud when they need sleep. And it changes everyday. So even if you put them to sleep 9 pm they still wake up 4:30 so you just miss out on more time at night.

Anonymous 0 Comments

There are a bunch of points you are missing:

Babies are not born with a circadian rhythm. For the first 3-4 months, they don’t sleep like adults at all. Adults sleep in 40-60 minute cycles. Babies do not. They begin to develop these cycles as they age.

Babies grow at an incredible speed. By 12 months, they have tripled their birth weight. A baby’s brain does 90% of its development before age 5. Growing like this takes a ton of energy. This is why babies eat so frequently, even through the night. They also need a lot of sleep so they have enough energy to grow. This is especially important for brain development.

Babies can’t make it through the day without sleeping. A normal baby, depending on age, will sleep 10-12 hours a night and 3-4 hours during the day. Skipping naps does not make them sleep longer at night. It actually makes them sleep worse because they become overtired. In order to develop properly, they have to sleep throughout the day and night.

TLDR: babies are not tiny adults. Their body systems and sleep patterns are very different. You can’t compare the sleep needs of an adult to the sleep needs of a baby. It’s like comparing apples and oranges.

Anonymous 0 Comments

Babies are so labor intensive to care for that it’s likely the ones that were awake and crying more were murdered.

Anonymous 0 Comments

This is speculation on my part but I think it’s because newborns are actually in 4th trimester.

Babies are born when they are not because their brains/ bodies are ready but because their head is as big as can be while still fitting through Moms pelvis. So human newborns are much more immature than other mammals when they’re born.

It makes sense for babies in utero to sleep most of the day because they are confined, dont have much coming into their senses and therefore don’t have much to learn, and dont want to hurt mom or themselves by getting too active. In utero they don’t have circadian rhythm because there isn’t enough light to sync to yet. Their main job is growing not learning so they can just be mostly asleep through it.

Anonymous 0 Comments

Aside what was already explained, babies have a lot of new information to be processed every day. Every day is a new thing to learn, seeing leaves for the first time, seeing new colors for the first time, new smells, new sounds, understanding what’s pleasant, what’s not…understanding the concept of pleasant, even. And we do burn calories thinking. So imagine…idk, buying a new computer and wanting to use photoshop + illustrator + After effects + powerpoint + 3D Max + Baldur’s Gate 3 + downloading 5 new games. Yeah, the computer will overheat because it’s too much.

Anonymous 0 Comments

Small factory with a high output requires more down time for maintenance. Plus the foreman is a baby. Nepotism. Don’t ask.

Anonymous 0 Comments

My 8 month old sleeps from 7pm-7am without waking up 9/10 nights (barring bad teething basically) also has 3 1-2 hour naps during the day. Babies are only happy for about 2-3 hours at a time without a nap. It is probably because they are growing very fast and are very weak proportionally to a grown person. Their whole job is to strengthen their muscles by doing normal daily tasks. Babies can barely move their head when they born, by a year they should be walking.