Circadian Rhythm Disorders (including Shift Work)

Circadian rhythms are physiological and behavioral changes in the body that occur on roughly a 24-hour cycle, sometimes called the internal body clock.  These rhythms regulate number of important processes in our body, including telling us when it’s time to go to sleep.   For most individuals, our internal clocks run longer than 24 hours, but are kept on the 24-hour day-night cycle by timing of light exposure (which affects melatonin release), and daily routines such as timing of meals and exercise.  

Circadian Rhythm Disorders occur when the body’s internal clock becomes out of synch with the usual day-night cycle, resulting in being awake when you desire to be asleep, being asleep when you desire to be awake or just feeling poorly as a result of being out of synch. There are several Circadian Rhythm Disorders and they fit into one of the following categories:

  • Delayed Sleep-Wake Phase Disorder
  • Advanced Sleep-Wake Phase Disorder
  • Non-24-Hour Sleep-Wake Rhythm Disorder
  • Irregular Sleep-Wake Rhythm Disorder
  • Shift Work Disorder
  • Jet Lag


The Circadian Rhythm Disorders

Delayed Sleep-Wake Phase Disorder or Delayed Sleep Phase Syndrome

A condition characterized by an inability to fall asleep until late at night, and the need to sleep late into the morning or even the early afternoon.  If given the chance, the individual will sleep well if sleep and wake times are much later than normal. This is most commonly seen in adolescents and young adults. It leads to problems when the individual must get up early for obligations (such as work or school).

Advanced Sleep-Wake Phase Disorder or Advanced Sleep Phase Syndrome

This condition is characterized by a need to sleep and wake up much earlier than normal.  This is most commonly seen in the elderly.  It leads to problems when the individual is unable to stay awake for desired evening activities.

Non-24-Hour Sleep-Wake Rhythm Disorder (Non-24)

A condition in which an individual’s day length is significantly longer than 24 hours. Most commonly seen in blind individuals who cannot sense the light-dark cycles of the day, this leads to sleep times getting later and later each day until they cycle completely around the clock.

Irregular Sleep-Wake Disorder (ISWD)

This condition is characterized by irregular sleep and wake periods, with at least three sleep periods spaced out during the day and night.  This is most commonly seen in the elderly, particularly in those with dementia. 

Shift Work Disorder

A condition in which an individual is required to work at a time when the internal body clock dictates a normal sleep time, leading to circadian rhythms being out of synch with the lifestyle and  thus they have serious difficulty in adjusting to the required schedule, and will feel poorly as a result of this.  They often end up with a lack of enough sleep time.

Jet Lag

In this condition, rapid travel across multiple times zones results in the body cycles being temporarily out of sync with each other and with the day-night cycle, resulting in sleepiness and/or insomnia, as well as a poor sense of being. This is a temporary condition that resolves with adjustment to the new time zone, which may take several days depending the number of time zones crossed and other factors.


Shift Work Disorder

The Problem

One quarter of the work force in industrialized countries perform some sort of shift work.  To ensure that a 24-hour production period is covered, 2 - 3 shifts are usually necessary in a day.  Millions of Americans are considered shift workers, including doctors and nurses, pilots, bridge-builders, police officers, customer service representatives, commercial drivers, and others.

Sleepiness is common among shift workers, especially during the night shift:

  • 80% of shift workers feel tired during their night shift.
  • 20% do fall asleep at night shift, compared to a much lower incidence among day shift workers.
  • Sleepiness in shift workers approaches levels similar to those seen in patients with primary sleep disorders like sleep apnea or narcolepsy.

Reasons for sleepiness in shift workers are multiple:

  • Shift workers rarely get enough sleep before their shifts.
  • Sleep after the shift is usually shortened by an average of one-third.
  • Even if adequate in duration, sleep near shifts is usually fragmented.  The day-night cycle (circadian rhythm) of the brain and the body may get disrupted when shifts occur on different times of the day.

Shift workers may have primary sleep disorders like sleep apnea or narcolepsy.  Consequences of sleepiness can be hazardous to the worker’s health and may cause sub-optimal work performance:

  • Near-crashes when driving after night shifts are common and they increase with increasing number of shifts.
  • Shift workers are at increased risk for a variety of chronic illnesses such as cardiovascular and gastrointestinal diseases.
  • Shift workers often complain of insomnia, disrupted sleep schedules reduced performance, difficulties with personal relationships, and irritability/depression
  • Sleepiness effects are like that of moderate alcohol consumption.
  • In history, several disasters have been attributed to poor performance of shift work:
    • The nuclear meltdown in Chernobyl
    • The Three Mile Island reactor accident
    • The Rancho Seco reactor near accident
    • The NASA Challenger space shuttle disaster.

The Solutions

There are multiple adjustments that may help a worker cope with the sleep-wake cycle disturbances of different shifts.  If our sleep-wake cycle does not adjust perfectly to our work schedule, especially when the schedule changes continuously, it may be useful to control our shifts schedule and our environment, instead.

  • Number of shifts worked in a row has not been shown to be an important factor in sleepiness.
  • Direction in which shifts rotate may be important.  Shifts that rotate forward (day -> evening -> night) are better tolerated.
  • Longer shifts may cause more problems.
  • Exposure to bright light (more than 2000 lux) increases alertness by inhibiting the secretion of a natural hormone called melatonin.  Melatonin promotes sleep, and its secretion increases in darkness.  It is also helpful to avoid exposure to bright light in the morning after a night shift, so that sleep after the shift is not disturbed.
  • Strategic napping is one way of getting enough sleep before a shift, and during the shift (if feasible).  A nap of no longer than 30 minutes can help.
  • Move bedtime closer towards the anticipated shift end time.  This can be done if there are a few days off between shift switches.
  • Avoid alcohol near bedtime since it disrupts sleep
  • Medications:
    • Caffeine is a stimulant.  Strategic consumption is important to get the beneficial alerting effect.  Caffeine starts working 30 minutes after consumption.  Its effect peaks at 2 hours and lasts for about 5 hours.  However, its use may lead to disruption of subsequent sleep (after the shift), tolerance may develop after continuous consumption which decreases its effectiveness, and the diuretic effect may be dehydrating.
    • Specific medications may be recommended by your Sleep Provider to help you fall asleep, stay awake when at work, and /or adjust or reset your internal clock.

If you still have problems, contact your provider and discuss if you need to see a sleep specialist.

Our Sleep Medicine team uses advanced technology to diagnose and treat sleep disorders at a variety of locations throughout the community. To schedule an appointment, call 216-778-5864.