Nod Ed: Newborns, Circadian Rhythms, and Sleep Training

April 6, 2018

Sorry—sleep training just won’t work before your baby turns 3-4 months old


The Takeaways:

  • Sleep (along with other activities) operates on a circadian rhythm, following the 24-hour cycle of day and night.

  • Babies don’t develop circadian rhythms until they’re about three months old. Until then, their sleep is on a cycle shorter than 24 hours.

  • Sleep training isn’t effective before the circadian rhythm develops, because the baby’s internal clock is not synchronized with the length of the day. So in the first few months they don’t get tired at the same time each day.  


The Full Story

Ever wonder why you always get hungry and tired at around the same times every day? Chalk it up to your circadian rhythm. A circadian rhythm is a cycle that lasts the length of a day, which includes your sleeping and waking cycles. Newborn babies have their own sleeping and eating cycles, but they’re much shorter than 24 hours, which is why—as you may have noticed—babies sleep and eat way more frequently than children and adults do.


Over time, as babies spend more time exposed to the natural light and dark of day and night, their sleeping and eating cycles get longer and eventually fall into traditional 24-hour patterns that synchronize with day and night. This generally starts around the 3- to 4-month mark, although—fun fact—some babies who haven’t been exposed to any artificial light (i.e. electric light) have been known to develop circadian rhythms as early as 2 months.


Unfortunately for exhausted new parents everywhere, sleep training just isn’t effective before the circadian rhythm develops. Since a newborn’s sleeping cycle is shorter than 24 hours, your baby could have very different levels of tiredness at the same time on two given days. So if you were wondering why two nights ago he was fast asleep from eight until midnight, while last night those were exactly the hours he wouldn’t sleep, well, now you know. This is why for the first few months, it’s not really possible to get your baby onto a regular schedule. The best thing you can do is let your baby sleep when they’re tired and eat when they’re hungry, even if it’s in the middle of the night. (Sorry!!)


But there’s light (and sleep!) at the end of the tunnel. Once the circadian rhythm develops, around that magical 3-to-4-month milestone, your baby will get tired at the same time each night. That’s when you can start sleep training, to make sure the tiredness translates into actually falling and staying asleep.


We know you’re probably eager to start sleep training, and we’re excited to start as soon as your baby is ready. Until then, sleep as much as you can, enjoy getting to know your little guy or gal, and know that a full night’s sleep is coming soon.



I Caroline Mcmillen, Joyce S M Kok, T Michael Adamson, Jan M Deayton, & Rachel Nowak. (1991). Development of Circadian Sleep-Wake Rhythms in Preterm and Full-Term Infants. Pediatric Research, 29(4), 381-4.


Menna-Barreto, L., Benedito-Silva, A., Marques, N., De Andrade, M., & Louzada, F. (1993). Ultradian Components of the Sleep-Wake Cycle in Babies. Chronobiology International,10(2), 103-108.


Mcgraw, K., Hoffmann, R., Harker, C., & Herman, J. (1999). The development of circadian rhythms in a human infant. Sleep, 22(3), 303-10.



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