How Circadian Rhythms Impact Sleep

The Sleep-Wake Cycle and Its Role in Health

High angle view of couple sleeping on bed at home

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Sleep is among the many physiological processes in the human body directed by circadian rhythms, a collection of interrelated internal clocks that oscillate independently throughout the day. It isn't surprising, then, that when a person's circadian rhythms are off they may experience problems such as insomnia or daytime sleepiness.

If you're dealing with sleep issues, having a general understanding of how circadian rhythms are established and how they can be thrown off can help you make sense of the steps you can take to get establish a healthy sleep schedule.

Factors That Effect Circadian Rhythms

External factors known as zeitgebers from the German for "time givers"—in particular light—and genetics are primary influencers of circadian rhythms.

Sun and Light

Both are important to circadian rhythms because photosensitive cells in the retina are directly connected to the anterior hypothalamus gland in the brain where the suprachiasmatic nucleus (SCN), or the body's pacemaker, is located. The SCN synchronizes many of the biological and physiological processes of the body, including sleep and wakefulness.

Sunlight entering the eye travels to the optic nerves, above which the X-shaped optic chiasm delivers the nerve signals to the SCN.

  • As morning sunlight increases at the start of the day, the visual system signals the SCN to activate receptors in the brain that stimulate the production of the stress hormone cortisol, leading to wakefulness and increased energy.
  • As sunlight decreases at the end of the day, the visual system signals the SCN to activate the pineal gland, the organ responsible for producing the sleep hormone melatonin.

Genetics

Certain genes have been found to help maintain circadian rhythms independent of external influences. The first such gene, called CLOCK (Circadian Locomotor Output Cycles Kaput), was identified by Dr. Joseph Takahashi and colleagues in 1994. Multiple genes have since been identified that constitute the body's core molecular clock.

Circadian Desynchronization

When a person's internal clock is misaligned, circadian disorders such as delayed sleep-wake phase syndrome (an inability to fall asleep) and advanced sleep-wake phase syndrome (in which sleep occurs prematurely) can develop. The degree of desynchronization is largely dependent on an individual's genetics and the extent to which day and nighttime patterns are interrupted.

Desynchronization can occur as a result of any number of circumstances, among them:

  • Time zone changes. Jet lag is a familiar circadian rhythm disruptor for people who travel.
  • Daylight savings time. The loss of a single hour can have a short-term effect on circadian rhythms.
  • Total blindness. Research has shown that people who are blind from birth frequently have difficulty with their sleep-wake cycle because of the lack of environmental light cues.This can lead to a condition known as non-24 sleep-wake rhythm disorder (non-24 SWRD).

Non-24 sleep-wake phase disorder can also occur in sighted individuals, albeit rarely. The cause is not entirely clear, but it seems to affect those with extremely irregular work hours, including those with ongoing shift work. For people dealing with insomnia or non-24 SWRD, a nightly 5-to-10 milligram dose of melatonin may improve sleep patterns.

Overcoming Circadian Rhythm Disorders

Irregular sleep patterns can interfere with health and quality of life. For example, nightshift workers often respond to the stress of their schedules by overeating, which can lead to weight gain and poor glucose control.

If faced with insomnia or non-24 SWRD, a nightly 5 to 10 mg dose of melatonin has been known to improve sleep patterns.

Ultimately, the best way to overcome circadian dysregulation is to reset your internal clock by taking steps to improve your sleep hygiene.

  • Maintain a regular sleep schedule: Go to bed at the same time every night of the week and use an alarm to wake yourself up at the same time every morning.
  • Don't take naps: Sleeping during the day decreases "sleep debt," so that you need less sleep at night. This can interfere with a regular sleep routine.
  • Don’t watch TV or read in bed: Stop any form of entertainment and turn off all electronics (including cell phones) at least 30 minutes before bedtime.
  • Avoid caffeine and alcohol several hours before sleep: Caffeine can overstimulate you. Alcohol may help you fall asleep but is likely to cause sleep interruptions and morning grogginess.
  • Keep the bedroom dark: Turn off all lights and tightly close curtains or window shades. Replace window coverings that allow light to shine through with room-darkening shades. Note that sleep masks can prevent sunlight from entering the eye and impede the environmental signals meant to stir you when it's time to wake up.
  • Turn down the thermostat: You're likely to sleep more soundly in a room that's cool. Even in winter, don't pile on too many blankets.
  • Keep it quiet: Sudden noises can cause momentary starts that interrupt otherwise restful sleep. If your partner snores loudly, explore anti-snore remedies or invest in a pair of earplugs.

A Word From Verywell

The causes of circadian disorders are not always clear and may take more than melatonin to set things right. If faced with chronic insomnia and daytime sleepiness, ask your doctor for a referral to a board-certified sleep physician who can help diagnose and treat your condition.

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  1. Quera Salva MA, Hartley S, Léger D, Dauvilliers YA. Non-24-Hour Sleep-Wake Rhythm Disorder in the Totally Blind: Diagnosis and Management. Front Neurol. 2017;8:686. doi:10.3389/fneur.2017.00686

  2. Solaiman SS, Agrawal R. Non-24-hour sleep-wake circadian rhythm disorder in a sighted male with normal functioning. J Clin Sleep Med. 2018;14(3):483-4. doi:10.5664/jcsm.7008

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