How Circadian Rhythms Impact Sleep

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, understanding how circadian rhythms are established and how they can be thrown off can help you determine what steps to take to establish a healthy sleep schedule.

Factors That Affect Circadian Rhythms

Light and genetics are external factors known as zeitgebers (German for "time givers") that are primary influencers of circadian rhythms. Certain health conditions may also affect circadian rhythms.

Sun and Light

Both sun and light 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 that constitute the body's core molecular clock have since been identified.

Health Conditions

Certain health conditions increase the risk of disrupted circadian rhythms, including:

• Certain genetic conditions, such as Smith-Magenis syndrome, Angelman syndrome, and Huntington’s disease
• Neurodegenerative diseases, such as Alzheimer’s disease, dementia, and Parkinson’s disease
• Conditions that cause damage to the brain, such as traumatic brain injuries, strokes, and brain tumors
• Autism spectrum disorder

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 (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 such as:

• 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).
  
• Lifestyle habits: Alcohol or illicit drug use, chronic caffeine intake, and nighttime exposure to artificial light (such as from a TV screen, smartphone, or very bright alarm clock) can disrupt circadian rhythms.

Overcoming Circadian Rhythm Disorders

Irregular sleep patterns can interfere with health and quality of life. For example, night shift workers often respond to the stress of their schedules by overeating (especially sugary and fatty foods), which can lead to weight gain and poor glucose control.

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 the room 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.

Summary

Circadian rhythms are a collection of interrelated internal clocks that wax and wane throughout the day. The causes of circadian rhythm disorders are not always clear, but it is known that irregular sleep patterns can interfere with health and quality of life. If you have sleep problems, try to reset your internal clock by taking steps to improve your sleep hygiene and talk with your healthcare provider for additional treatment options.