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Understanding Circadian Rhythms

What is a Circadian Rhythm? How do circadian rhythms work, and how do they affect sleep?


Circadian rhythms are driven by your body’s internal master clock—it controls things like your sleep/wake cycle, eating habits and digestion, and your body temperature.  Usually it is synchronized with the day-night cycle This biological process helps produce the hormone melatonin in the evening, influencing you to feel sleepy, and slows that production in the morning when you’re exposed to light, which allows you to wake up and be alert. 


What Is A Circadian Rhythm? 

  • Your body’s biological clock located in the brain in the suprachiasmatic nucleus (SCN) produces circadian rhythms and regulates the timing of things in your body like when you want to sleep or eat.
  • These rhythms are named circadian meaning “about a day” because they tend to occur at least every 24-hours.
  • Natural factors in your body produce circadian rhythms but signals in the environment, like daylight, as well as exercise and temperature, also affect them.
  • Problems can occur when your biological clock is not lined up with the day-night cycle. This type of abnormality has been linked to health conditions like obesity, diabetes, depression, and sleep disorders.


What Controls Circadian Rhythms?

Circadian rhythms ensure that your body’s processes are synched and optimized during each 24-hour period. They aren’t unique to humans though—they also help some animals sleep and stay safe in their shelters at night, while causing some animals to be awake and hunt at night and sleep during the day.

In humans, circadian rhythms control many body processes. For instance, your digestive system produces proteins to make sure you eat on schedule, and the endocrine system regulates hormones to match your energy expenditures during the day.

The circadian rhythms for each of the systems in the body are strongly influenced by a master clock in the brain, the suprachiasmatic nucleus, sending signals at the appropriate times.


Why Do Circadian Rhythms Matter?

When we talk about circadian rhythms, it’s mostly in relation to sleep. That’s because when our circadian rhythm is out of sync, our sleep is, too. Without the right signals from your body’s internal master clock, you might not fall asleep, have fragmented or sleep poorly, or wake up too early and not be able to fall back to sleep. These may indicate presence of a circadian rhythm-related sleep disorder.


What Are the Most Common Circadian Rhythm-Related Sleep Disorders?

Delayed Sleep Phase Disorder: Some people feel alert at night and often can’t go to sleep until the middle of the night, causing them to sleep well into the following day.

Advanced Sleep Phase Disorder: Some people fall asleep early in the evening, from 6:00-9:00 p.m., and wake in the early hours of the morning at say, 2:00 a.m. This often happens to people in their later years.

Jet Lag: This is when circadian rhythms have been disturbed by air travel through two or more time zones. It’s difficult for people to function well at first when they’re in a new time zone.

Shift Work Disorder: Night workers whose schedules conflict with the body’s natural circadian rhythm are often sleepy and have ongoing tiredness.


How Does a Circadian Rhythm Get Out of Sync?

A disrupted circadian rhythm can occur either due to an internal malfunction or a mismatch between your body clock and external factors like social or work environment (for example, if you’ve stayed up very late watching a movie or you have to work the night shift). Additional factors that can disrupt your circadian rhythm are:

  • Changing work shifts a lot
  • Not keeping consistent sleep and wake times
  • Insufficient light exposure during the day and bright light exposure at night
  • Poor sleep habits (drinking caffeine or alcohol too close to bedtime, lack of a bedtime routine, looking at your phone or computer too late at night)
  • Jet lag
  • Medications


Could You Have a Circadian Rhythm Disorder?

If you experience insomnia, daytime sleepiness, difficulty waking up, depression, or sleep loss, talk to your healthcare provider. She or he may recommend that you keep a sleep diary or meet with a sleep specialist. Treatment options like lifestyle and behavior therapy (getting more daylight exposure, limiting naps, getting exercise, and practicing good sleep habits) as well as medication and chronotherapy (shifting your sleep/wake cycle by progressively delaying sleep over time) can alleviate the effects of circadian rhythm sleep disorders.