Sleep Rhythms: Circadian, Ultradian, and Sleep Shifts
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Despite what your work schedule says or what late-night happy hour you want to hit, your body knows when it’s time to sleep. This natural inclination is dictated by a multitude of both internal and external factors—many of which are totally under our control.
Our sleep rhythms are as unique as our fingerprints, but there are definitely some commonalities we all experience. And when you learn how your personal ebb and flow of energy works, you can learn how to work with it to get the most restful, restorative sleep possible.
What is Circadian Rhythm?
Perhaps the most common name when it comes to sleep rhythms is circadian rhythm. This 24-hour biological clock runs in the background of our lives, telling our bodies when it’s time to sleep, wake up, eat—you name it. It responds to the light-dark cycle of the day and is what makes us feel more awake when the sun is out and sleepy when it’s dark.
The main internal factor that regulates our circadian rhythm is melatonin. This hormone is produced by the pineal gland in our brains and is responsible for making us feel sleepy. The production of melatonin is dictated by the light we’re exposed to.
When it’s dark, our brains produce more melatonin, and we feel sleepy. In contrast, when it’s light out, melatonin production decreases, and we feel more awake. Ever wonder why you’re ready to hit the hay way earlier in the winter than in the summer? That’s because there’s less sunlight during winter days, which sends a cue to our brains to produce more melatonin sooner.
Genetics plays a role in how our circadian rhythms work, too. Some people are simply early risers, while others are night owls. This natural variation is dictated by our genes and can be further influenced by our lifestyle choices.
What is Ultradian Rhythm?
A little lesser known is ultradian rhythm, which is really just an umbrella term to describe a large number of biological clocks that we cycle through multiple times within a 24-hour period.
There are all sorts of ultradian rhythms at play in our bodies, but one of the most relevant to sleep is what’s called the Basic Rest and Activity Cycle (or BRAC). The legitimacy of this rhythm is still under debate, but according to its founder, Nathaniel Kleitman, we all cycle through 90-minute periods of high and low energy.
During the day, our energy and alertness levels ebb and flow in response to this ultradian rhythm. More research needs to be done to understand ultradian rhythms and their impact on sleep, but if you find yourself nodding off at the same time every day, it could be worth noting.
Sleep Rhythm Shifts
In a perfect world, our internal clocks would stay on the same schedule forever. But, of course, life happens, and our bodies’ sleep rhythms have to adapt. Here are some of the most common sleep rhythm disruptions:
- Shift work: Working odd hours—nights, weekends, early mornings—can take a toll on our natural sleep rhythms. Studies have shown that shift workers are more likely to experience insomnia and other sleep disorders.
- Jet lag: This one’s pretty self-explanatory. When we travel across time zones, our bodies have to readjust to the new light-dark cycle. It can take a few days (sometimes even a week) for you to return to your usual sleep patterns and feel like yourself again.
- Pregnancy: Hormone fluctuations during pregnancy can cause all sorts of disruptions to our bodies, including our sleep rhythms. It’s not uncommon for pregnant women to experience insomnia, as well as excessive daytime sleepiness.
- Age: The older we get, the less REM sleep and slow-wave sleep we tend to get. This can throw off our natural sleep rhythms and make it more difficult to get a good night’s rest.
- Illness: When we’re sick, our bodies work overtime to fight the infection. This can lead to disruptions in our sleep patterns and make it more difficult to fall asleep and stay asleep. The medications we take to get better can also interfere with sleep.
- Lifestyle changes: Big transitions like having a newborn, starting a new job, or moving to a new city can all have an impact on our sleep rhythms. It can take some time for our bodies to adjust to the new normal and establish healthy sleep habits.
There are all sorts of things that can throw off our sleep rhythms. But the good news is, with a little bit of effort, it’s possible to get them back on track.
How to Optimize Your Sleep Rhythm
Prioritizing sleep is key to maintaining a healthy sleep rhythm. Here are a few simple things you can do to make sure you’re getting the most out of your shut-eye:
- Create a soothing bedtime routine: Try taking a bath, reading a book, or stretching. Doing the same things every night signals to your body that it’s time to wind down and prepare for sleep.
- Establish a consistent sleep schedule: Going to bed and waking up at the same time each day helps to keep your body’s internal clock on track.
- Limit screen time before bed: The blue light emitted by screens can interfere with sleep. Try to avoid using electronics for at least an hour before you go to bed.
- Create a restful environment: Make sure your bedroom is dark, quiet, and cool. This will help you fall asleep and stay asleep through the night.
- Get regular exercise: Exercise has countless benefits, including improving sleep quality. Getting just a half hour of exercise a day can make a big difference.
- Limit caffeine and alcohol: Both of these substances can interfere with sleep.
If you’ve gone through all of these tips and you’re still struggling to get a good night’s rest, it might be time to talk with a doctor. There are a variety of sleep disorders that can disrupt our natural sleep rhythms. But with the help of a medical professional, you can identify any underlying sleep disorders and come up with a plan to treat them.
There’s no magic cure for getting a good night’s sleep. But learning how to work with your natural sleep rhythms can help you get the most out of your shut-eye. Establishing a regular sleep schedule, limiting screen time before bed, and getting regular exercise are all good places to start.
If you’re still struggling to sleep, talk with a doctor about any underlying sleep disorders.
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Cleveland Clinic. (2021). Jet Lag. https://my.clevelandclinic.org/health/diseases/12781-jet-lag
Cleveland Clinic. (2022). Melatonin. https://my.clevelandclinic.org/health/articles/23411-melatonin
Division of Sleep Medicine at Harvard Medical School. (2007). Individual Variation and the Genetics of Sleep. https://healthysleep.med.harvard.edu/healthy/science/variations/individual-variation-genetics
Hashmi AM, et al. (2016). Insomnia during pregnancy: Diagnosis and Rational Interventions. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017073/
Kleitman N. (1982). Basic Rest-Activity Cycle-22 Years Later. https://pubmed.ncbi.nlm.nih.gov/6819628/
Lavie P. (1992). Ultradian Cycles in Sleep Propensity: Or, Kleitman’s BRAC Revisited [ABSTRACT]. https://link.springer.com/chapter/10.1007/978-1-4471-1969-2_13
Li J, et al. (2019). Sleep in Normal Aging. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5841578/
National Institute of General Medical Sciences. (2022). Circadian Rhythms. https://www.nigms.nih.gov/education/fact-sheets/Pages/Circadian-Rhythms.aspx
ScienceDirect. (2010). Ultradian Rhythm [ABSTRACT]. https://www.sciencedirect.com/topics/medicine-and-dentistry/ultradian-rhythm
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