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Circadian Rhythm Disorders

Your body runs on a 24-hour schedule during which exposure to light and darkness affects your internal clock within the brain, a master pacemaker that regulates your circadian (24-hour) rhythms. The sleep-wake cycle is one of the most obvious circadian rhythms controlled by the internal biological clock, but there are other circadian rhythms within the body including hormones and body temperature to name a few. There are several important cues that help regulate the timing of the circadian clock within the brain, including the light-dark cycle, rest and activity, and melatonin. As long as the body’s internal clock is synchronized with the outside world, we are in harmony with our environment allowing us to sleep well and to be fully alert when desired. However, when the body’s internal clock is out of synchrony with the desired schedule of the outside world, then pathology results in some degree of insomnia and/or excessive sleepiness. As a result, you may also experience decreased job or academic performance, irritability, depression and difficulties with interpersonal relationships.

Circadian rhythm disorders include several different disorders affecting the timing of sleep and wakefulness and are generally considered pathological when either excessive sleepiness or insomnia interferes with our ability to function within a desired sleep-wake schedule. Circadian rhythm disorders may occur at any age. They are more commonly found in shift workers, adolescents, pregnant women, the elderly, blind people or people with impaired neurocognitive or physical impairment, but they can also be found otherwise normal and healthy individuals.

Common circadian rhythm disorders:

Shift-Work Sleep Disorder. Approximately 25% of the American work force works on a rotating or night shift schedule. Shift work sleep disorder is characterized by excessive sleepiness when you wish to be awake (often during the night shift) and difficultly sleeping when you wish to be in bed.

Approximately 25% of employed men and 17% of employed women in the United States currently work either on the night shift or on a rotating shift schedule. Shift workers perform critical functions in hospitals, on police forces, as emergency personnel, and in the transportation and manufacturing industries. Shift workers battle the natural sleep-wake rhythm of the body. There is a natural inclination to sleep between the hours of midnight and 6:00 AM, just when they need to be most alert to maximize their productivity. Shift work is generally defined as night work or any time other than the usual “nine-to-five” business day. However, it also includes shifts that call for rotating or periodically changing hours, split shifts when an employee works all or part of two consecutive shifts, and extended shifts when working longer than the typical eight-hour day.

Shift-work sleep disorder is characterized by excessive sleepiness when you wish to be awake (often during the night shift) and difficultly sleeping or insomnia when you wish to be in bed. The insomnia may occur either when trying to sleep during the day after a night shift, or when trying to shift back to a regular schedule of sleeping at night. Indeed, problems can also be exacerbated when trying to shift back to a normal schedule on days off from work when trying to be on the same schedule as the rest of the family. The constant rotation of schedules prevents the brain’s internal clock from synchronizing with the external environment leading to excessive sleepiness or insomnia.

Effects of Shift Work
Of those who work the night shift, 40-80% have sleep complaints, and 5-20% report moderate to severe sleep problems. Excessive sleepiness while working on the night shift not only leads to decreased productivity, but can have disastrous consequences as has been well documented from several famous man-made disasters caused by fatal errors that have occurred while working on the night shift. The Chernobyl (1986) and 3-Mile Island (1979) nuclear disasters, as well as the Exxon Valdez oil tanker grounding (1989), all occurred between the hours of 12:00 and 4:00 AM and were found to be caused errors made secondary to excessive sleepiness while working on the night shift. Although the space shuttle Challenger explosion (1986) occurred at 11:38 AM, the erroneous decision to launch the shuttle was made by the team working during the night shift.

Sleep deprivation can lead people to think and move more slowly, make more mistakes, and become more forgetful. Lack of sufficient sleep can cause irritability, impatience, anxiety, depression and lowered productivity. Sleep deprivation costs U.S. businesses $150 billion a year in accidents and decreased productivity. Shift workers are also more likely to experience stomach problems, menstrual irregularities, illness, weight gain, heart problems, high blood pressure, and a higher risk for diabetes than day workers.

Tips and treatment for night shift workers
There are several tips and interventions that may be very helpful for patients who work the night shift. As much as possible, you should try to maintain a strict sleep-wake schedule. Keeping the same schedule, even on days off from work, is the ideal way to synchronize your brain’s internal clock with the desired external schedule. Although it is sometimes not possible to maintain the same schedule on days off, you should avoid frequently rotating shifts. The more the schedule shifts, the more difficult your brain’s internal circadian clock will have in adapting to the schedule, and the more insomnia or excessive sleepiness you will experience.

While working the night shift, it is important to minimize or avoid caffeine-containing products, especially during second half of the shift before going home, since any stimulant consumption will prevent you from being able to initiate or maintain sleep once going to bed at the end of the shift. Although keeping the work environment well lit with bright light can help maintain alertness while working at night, you should also avoid bright light exposure prior to going to bed since it will decrease your ability to sleep. If there is daylight at the end of the shift and you plan on sleeping once you get home, it is recommended to wear sunglasses during the drive home. It is also very important to keep the bedroom dark and quiet by using heavy curtains to keep out sunlight and turning off or unplugging the telephone so that sleep will not be disrupted.

Bedtime Tips

  • Darken the bedroom and adjust the bedroom temperature to simulate nighttime.
  • Unplug the telephone and eliminate other potential distractions as much as possible
  • Avoid caffeine for at least five hours before bedtime
  • Avoid exercising within at least three hours of bedtime

Driving Tips

  • Do not drive a motor vehicle if excessively sleepy
  • Nap before driving home, if possible, if you are excessively sleepy
  • Car pool, if possible, and have the most alert person do the driving
  • Consider taking public transportation if available
  • Wear sunglasses at the end of the shift when driving home if there is sunlight and you wish to sleep when getting home.

Tips for Work

  • Take short breaks throughout your shift to break up monotony
  • Exercise during breaks if possible
  • Try to work with a partner since conversation can keep you more alert
  • Don’t leave the most boring tasks for the end of your shift since this is when you feel most drowsy

Delayed Sleep Phase Syndrome. This disorder occurs when the body’s internal circadian clock is somewhat longer than 24-hours or the individual has a natural tendency to be a “night owl”, leading to habitually late bedtimes, not feeling tired in the evening and difficulty initiating sleep. These patients also have difficulty waking up in the morning and can sleep through the alarm clock, possibly leading to missed school or work.

In the normal condition, the brain’s internal circadian clock is very close to 24 hours, just like the natural 24-hour day. However, some individuals have an internal circadian clock that is somewhat longer than 24-hours or have a natural tendency for habitually late bedtimes. In patients with delayed sleep phase syndrome, this tendency is exaggerated leading them to not feel tired in the evening and causing a pathological difficulty initiating sleep at night. These patients commonly have sleep-onset insomnia, but can maintain sleep well once sleep has finally been initiated.

Patients who are “night owls” are most likely to suffer from delayed sleep phase syndrome. These patients also have difficulty waking up in the morning and can sleep through the alarm clock, possibly leading to missed school or work. Although patients with delayed sleep phase syndrome feel tired and sleepy in the morning, they feel wide awake in the evening. This disorder is most commonly seen in adolescence to young adulthood when the brain’s biological clock tends to naturally slow down at the time of puberty. If you have a teenager sleeping in until late morning or noon on weekends, difficulty getting to bed on school nights and difficulty getting up for school, you should suspect delayed sleep phase syndrome as a possible cause.

Delayed sleep phase syndrome can be worsened or exacerbated in the face of inadequate sleep hygiene, a common problem in adolescence. In the age of iPhones, text messaging, video games, social networking, and other electronic media, many kids have a long list of excuses to delay bedtimes. By going to bed late and getting up early for school, they tend to accumulate a profound sleep debt by Friday night and then pay back that debt on the weekends, often sleeping in until late morning or noon.

Sleeping in for an extra 3-5 hours on days off resets the biological clock to a later or delayed “time zone”. For a teenager in Ohio living in Eastern Standard Time, it is common for them to live their weekend as if they were living in the Pacific or California time zone. After two nights of going to bed at midnight or later on the weekend, they need to come back to the Ohio time zone and go to bed before 9-10:00 PM for school the next morning. Unfortunately, their brain is not ready to go to sleep that early and they may be unable to fall asleep even if they make the effort to go to bed at a reasonable time. As a result, they wake up sleep deprived the next morning, and the vicious cycle repeats with the accumulation of another sleep debt during the week waiting to be paid back the following weekend, all the while leading to decreased school performance. (See Sleep Hygiene).

Tips for Treating Delayed Sleep Phase Syndrome

  • Maintain a strict sleep-wake schedule even on weekends or days off from work or school, and, most importantly, maintain a strict wake-up time.
  • Minimize bright light in the evening.
  • Maximize bright light in the morning and consider having a bright light on a timer to automatically turn on in the bedroom at the same time each morning.
  • It is often helpful to have an “unplugged” hour prior to bedtime with all electronic devices tuned off one hour before bedtime and to try reading with indirect light instead.
  • Your physician may recommend starting melatonin 1-3 mg approximately 3 hours prior to bedtime. Melatonin can “phase advance” the brain’s circadian clock to an earlier bedtime.
  • Avoid exercise approximately 3-5 hours prior to bedtime, but instead try exercising in the morning upon awakening.

Advanced Sleep Phase Syndrome. Patients with this disorder are known as "larks" and have a natural tendency to awaken early in the morning even without an alarm, yet have difficulty staying awake in the evening. The brain’s circadian clock tends to speed up as we get older, sometimes leading to a natural circadian rhythm that is somewhat shorter than 24 hours. For this reason, advanced sleep phase syndrome can often occur in elderly individuals. When affected by this disorder, the individual falls asleep at a much earlier time than the desired clock time and complains of excessive sleepiness in the evening, yet experiences early morning insomnia and an inability to fall back asleep when awakened before the desired alarm.

Irregular Sleep-Wake Rhythm. This disorder is a chronic condition during which sleep and wake periods are disorganized and vary throughout a 24-hour period. Sleep is broken up in short periods at night and long naps during the day.

Jet Lag Disorder. Traveling across more than 2-3 time zones in a short period of time creates a misalignment between the brain’s internal clock and the external environment or new time zone leading to either sleepiness or insomnia depending on the new time zone.

Traveling across many time zones over a very short period of time is common today with jet travel. In 8-14 hours we can now fly directly to Europe, Japan, Australia or China and suddenly find ourselves in a completely different time zone. Unfortunately, our brain’s biological clock is unable to shift time zones as quickly, creating a misalignment between the brain’s internal clock and the external environment. Indeed, it may take the brain’s circadian clock several days, and sometimes well over a week, to fully adapt to the new time zone.

During this misalignment, it is natural to feel sleepy at the new destination even though it may be daytime if it happens to coincide with night-time in your habitual or home time zone. On the other hand, it should come as no surprise that you may experience insomnia, either difficulty getting to sleep or waking up before the desired rise time, if the timing of the insomnia corresponds to daytime in your originating or home time zone.

Business travelers, athletes, and concert performers need to pay particular attention to the effects of jet lag if they expect to perform at their highest level when arriving at their new destination. Daytime fatigue and sleep disturbances can lead to cognitive impairment such as thinking and moving more slowly, making more mistakes, and becoming more forgetful. Lack of sufficient sleep can cause irritability, impatience, anxiety, depression and lowered productivity.

Tips to Minimize Jet Lag
Planning ahead and intervening when necessary should always be considered prior to traveling and when arriving at your new destination to minimize the effects of jet lag. If you plan to travel across 5 or more time zones, you may wish to consider leaving early enough so that you arrive at your destination several days before any important meeting or performance. When traveling across less than 5 time zones, it is also important to remember that it is generally much easier to travel westward which involves a “phase delay” of the circadian clock and simply requires staying up a few hours later for bedtime. Most people find it more difficult to go to bed several hours earlier than the desired bedtime as occurs when traveling eastward, causing a “phase advance” of the circadian clock.

Some people find it helpful to approximate the new time zone several days prior to traveling by going to bed earlier if traveling eastward or later if traveling westward. Physical activity during the new circadian day and making a concerted effort to integrate within the new time zone are generally good rules of thumb to adapt quickly to a new time zone.

Medications may be helpful in certain cases for time zone travelers, but you should consult with your physician for a treatment regimen best suited for your specific needs to address the number of time zones to be traveled. Melatonin is available over-the-counter and the brain’s circadian clock is sensitive to melatonin. Melatonin given at the appropriate time can shift the timing of the circadian clock to adapt more quickly to a new time zone. However, melatonin given at the wrong times can make the situation worse and highlights the need to discuss the use of such medications with your physician before traveling. Sedative hypnotics, such as Ambien, may be used to promote sleep, whereas stimulants to promote wakefulness may also be considered in some circumstances, particularly when traveling across many time zones. However, you should discuss the appropriateness and timing of such medications with your physician.


Diagnosis of circadian rhythm disorders is based on a clinical evaluation and often involves the use of a sleep diary. Many patients with a circadian rhythm disorder, however, may also have one or more other sleep disorders. If another sleep disorder is suspected, you may be asked to undergo an overnight sleep study or polysomnogram.

For More Information

For more information about circadian rhythm disorders, visit the American Academy of Sleep Medicine at http://www.sleepeducation.com and the National Sleep Foundation at http://www.sleepfoundation.org

circadian rhythm disorders, shift-work sleep disorder, delayed sleep phase syndrome, advanced sleep phase syndrome, jet lag, irregular sleep-wake rhythm


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