Infant Sleep Update: Why Young Babies “Mix Up” their Days and Nights

by Jennifer Goldbronn, MAS, RD

Today, we will talk about how light/dark cycles affect how babies sleep at various ages. Understanding how these cycles affect babies' sleep patterns will help you understand yet another reason why newborns wake up so often during the night. (Peirano 2003)

In adults, sleep and wake time is regulated by 2 internal “clocks,” one that responds to the light/dark cycle and one that is based on a need for sleep that builds up during the waking hours. The clock that responds to the light/dark cycle is located in the brain and uses hormones to regulate activity and sleep over each 24 hour period. This system is called the “circadian rhythm.” Circadian rhythms are not functioning in newborns and that is a good thing because newborns need to wake both day and night for care and to be fed enough to grow well and stay healthy. (Peirano 2003)

When Circadian Rhythms Develop: “My baby has his days and nights mixed up!”

You may have heard about (or experienced!) erratic newborn sleep patterns. It seems that newborns have their days and nights “mixed up.” It’s true! A young baby’s sleep patterns do not follow the light/dark cycle (awake during the day, sleeping at night) like adults’ do. Babies’ sleep patterns don’t start to follow light/dark cycles until about 6 weeks of age, and circadian rhythms are not fully developed until 12 to 16 weeks. This does not mean that you should expect your baby to sleep through the night at 16 weeks. It means that you’ll start to see a clear pattern of wakefulness during daytime hours and a longer stretch of sleep during the night by the time your baby is 12 to 16 weeks old. (Peirano 2003, Heraghty 2008)

While you can’t do anything hurry this process, there are a few things that may influence how quickly your baby develops circadian rhythms after the first 6 weeks. Type of feeding (formula-fed vs. breastfed), environmental lighting (lights on in house in the evening hours), and infant age all can affect the development of your baby’s circadian rhythms. One study found that breastfed infants, 1st born infants, and girls developed circadian rhythms earlier than other infants (but there was still a broad range of 8-16 weeks). (Mirmiran 2003)

How to Work with Your Babies’ Natural Rhythms

Here are a few things you can do to work with (instead of against) your baby’s natural rhythms.

1. Keep the room where your baby sleeps dark at night. When your baby wakes during the night, keep the lights low when taking care of his needs, such as feeding or diaper changes.

2. Expose your baby to natural light during the day.

3. Follow a consistent bedtime routine that includes slowing things down in the evening, including lowering the lights and noise level.

The first 6-weeks of your baby’s life are especially challenging; learning about your baby’s sleeping and waking patterns can help you understand why your young baby may seem like he doesn’t follow a consistent “schedule.” You are going to need help during those weeks when you are most sleep deprived yet need to take care of your other responsibilities. Your baby eventually will learn that nighttime is for sleeping. Until then, here are some past posts to help you deal with the inevitable sleep deprivation you will experience while your baby needs so much nighttime care.

Can Little Changes Lead to a Little More Sleep? 
Thoughts from a Sleep Deprived Mom
Tips from the Trenches: Surviving Sleep Deprivation
Weighing the Pros and Cons of Napping

References

Peirano P, Algarín C, Uauy R. Sleep-wake states and their regulatory mechanisms throughout early human development. J Pediatr. 2003;143:S70-9.

Mirmiran M, Maas YGH, Ariagno RL. Development of fetal and neonatal sleep and circadian rhythms. Sleep Medicine Reviews. 2003; 7 (4): 321-334.

Heraghty JL, Hilliard TN, Henderson AJ, Fleming PJ. The physiology of sleep in infants. Arch Dis Child. 2008;93(11):982-5.