Circadian Rhythm Sleep Disorders


With industrialization, we have gone to a 24-hour society. Not only are there consumers who are awake at all hours, shopping, driving, dining, and recreating; but there are industries oriented towards 24-hour production. This has led to increasing proportions of our society involved in shift work. About 20% of American workers are engaged in some form of shift work system. Shift workers have higher incidence of health problems, particularly gastrointestinal complaints. Between 40% and 80% of shift workers complain of difficulty sleeping. In one study, more than half of night workers admitted that they slept on the job at least once a week. The problem is usually exacerbated in individuals with dual roles, particularly women who also function as caretakers of their children and household managers. In addition, the shift worker may also have another coexistent sleep disorder further degrading sleep quality.

One must keep in mind from the start that problems arising from shift work are complex and not isolated to the timing of the work schedule. There are heavy influences of social and domestic factors. Social and family responsibilities are constant emotional and psychological stresses affecting the shift worker who has to chose between them and sleep. Frequently, various aspects of the shift worker's relationships are sacrificed in favor of others. The priority of what is sacrificed may lead to increased interpersonal stresses. For instance a male shift worker may sacrifice intimacy with his wife to preserve roles as companion to his wife; a female shift worker may sacrifice companionship to preserve her role as caregiver to her children. Family and friends may not understand the issues the shift worker faces in choosing which roles are important. Similarly the shift worker may be inaccurately prioritizing a role which he feels is important to his significant others. The shift worker may also feel an emotional loss from the inability to participate easily in social functions that continue to be limited to a traditional daytime clock, such as going to a museum or football game.

To compound matters, the shift workers natural biologic rhythms and tendencies to sleepiness and alertness have a very strong pressure to remain entrained to the regular day-night cycle. Indeed, the adaptation to a new sleep-wake cycle takes many days. During this time the individual suffers from primary sleep disruption while trying to sleep during daytime hours leading to a sleep deprived state. While at work, the individual is attempting to function highly at times that would normally be "down-time". During the adjustment period, the cycles of body temperature, hormonal release, and sleep-wake are in complete disarray. All of these factors lead to adverse effects on mood, productivity and sense of well being. The tendency for these biologic rhythms to return to the traditional day-night schedule is great. The majority of shift workers flip back to the traditional schedule during time off, thus having to start the adjustment process all over, even when on a permanent night shift schedule.

To date, an accurate method of predicting the most suitable shift worker has not been established. There are individual characteristics that may indicate difficulty coping with shift work. These include physical factors such as age over 50, medical conditions such as heart disease, diabetes and gastrointestinal problems, and coexistent sleep disorders. Psychological factors such as alcohol or drug abuse, psychiatric illness, and "morning-type" personality characteristics play a role. Social aspects such as having to maintain a second job, or heavy household responsibilities also signal potential problems with coping with shift work.

Similarly, there is no "ideal shift work schedule". Shift work schedules must be tailored to the type of work being done. Jobs requiring heavy manual labor or sustained vigilance are not suitable to 12-hour shifts for instance. With recent medical understanding of how the brain and body adapt to changes in sleep-wake schedules, certain aspects of shift schedules are now known to be particularly difficult. Features can be built in to the system to enhance adaptation. Rotating shift schedules which work against the body's methods of adaptation have been identified as likely to cause shift work coping problems. Rotating shifts that change once a week ("weekly rotation") allow just enough time for the body to adapt to the new schedule when it comes time to change to a new schedule. Shifts that rotate backwards, from first to third to second shifts, work against the body's natural tendency to forward rotate. Shift schedules in which first shift starting times are before 7:00am have also been identified as potentially associated with coping problems. A rapid rotating shift which is gaining popularity in Europe consists of two day shifts, then two evening shifts, then two night shifts, followed by two days off. This schedule capitalizes on not having to adapt to a night schedule or worry about slipping back to a day schedule during time off. The two night shifts are fraught with fatigue, however, and may not be suitable for certain tasks. In the United States, chronohygiene is increasingly being used to enhance adaptation to the night shift. This includes very bright illumination of the work place followed by careful light shielding on the commute home and during the sleep period with meal breaks appropriately timed to facilitate biological adaptation to the night cycle.

The intervention with the greatest impact that can take place in the work place regarding shift work coping abilities is education. Management benefits from training in recognizing a problem that leads to poor employee morale, increased absenteeism and high job turnover (leading to higher recruiting and retraining costs) and to higher medical and accident costs. Management also benefits from education regarding the recent findings in sleep medicine research which help select appropriate shift work schedules and methods which enhance adaptation to shift work. Workers benefit from education regarding good sleep hygiene and how the various social and biological factors affect their ability to adapt to shift work. They also benefit from instruction on how to control these factors, optimizing those which enhance their ability to cope with shift work and minimizing the factors which are working against them. Supportive counseling to address social issues affecting shift work coping can also have a great impact.


Rapid transit has markedly influenced the range and scope of international business. No longer are business meetings solely a part of big business; medium and even small businesses are taking advantage of the availability of jet travel to conduct coast-to-coast and international business in person. Such air travel can be extremely physically demanding leading to significant fatigue and physical complaints while on the trip and upon return.

A significant part of long flight-time travel is due to the physical and emotional stresses that occur apart from those resulting from time zone changes. These stresses include low cabin humidity, low cabin pressure, noise, vibration, cramped seating, and travel stress and anxiety. The resulting symptoms include dry eyes, muscular soreness and cramps, headaches, swelling and bloating, and occasional dizziness. These symptoms are common to all long flight-time air travel regardless of whether time zones have been crossed (for instance from North to South America). These symptoms generally do not last longer than the first 24 hours.

In contrast, jet lag is an impairment of one's sense of well being that results from the conflict between the body's internal clock and the external time cues of the new destination time zone. The symptoms of jet lag last much longer than those common to long flight-time travel because the body's mechanisms of resynchronizing with the new environment are delayed and may not be complete for several days after arrival. The effects of time zone changes are usually shorter lived than those experienced in the adjustment of changes in shift work schedule. This is because the time cues such as daylight, meal times and social interactions in the destination environment reinforce synchronizing to the new time zone. These same cues are working against adjustment of the shift worker's internal clock.

There are three major components to jet lag: external desynchronization, internal synchronization, and sleep deprivation. External desynchronization refers to the conflict between the internal clock with the external time cues. The internal clock sets the timing of sleepiness, alertness, hunger etc. With as little as a 3-hour time zone difference there arises a dissonance between these internal signals and the external cues such as sunrise and meal times. As the individual is exposed to these new external time cues, the internal clock adjusts to the new time zone. This process may take several days.

Internal desynchronization occurs due to the process of readjustment of the internal clock. The internal clock consists of several biological factors that rise and fall with the daily clock. These include the sleep-wake cycle, the body temperature cycle, and various hormonal cycles. Each system resets or adjusts itself differently, some adjusting forward with the clock, some backwards. Some systems will adjust rapidly others more slowly. During this adjustment period, the various systems are not in harmony with each other or the environment.

The third component of jet lag is sleep loss. This occurs beyond the sleep loss associated with long flight-time travel. This sleep loss is a result of the internal and external desynchronization components. The deprivation of good quality sleep adds to the fatigue and malaise of jet lag. The amount of sleep loss also seems to influence the desynchronization components. When sleep loss is great, the pressure to get sleep overcomes some of the desynchronization and individuals sleep longer. When sleep loss is minimal, travelers are more susceptible to the influences of desynchronization and sleep more poorly.

Several factors affect the ability to adjust to trans-meridian travel. The direction of travel affects adaptation. Eastward travel is associated with more fragmented sleep and higher levels of daytime sleepiness. Age over 50 is associated with more frequent awakenings and poorer quality sleep. There are some indications that the more seasoned frequent traveler may adapt to time changes better than infrequent flyers. Personality types (larks vs. night owls) may also influence adaptation, again depending on the direction of travel.


The sleep phase syndromes are also arising from a conflict between the internal and external clocks. In shift work and jet lag, the external clock has been modified so that it is incongruent with the internal clock. In the sleep phase syndromes, it is the internal clock which is shifted with respect to the external clock.

Delayed Sleep Phase Syndrome (DPSP) is more likely to adversely affect conventional daytime workers than their evening or night shift counter-parts. Indeed, many sufferers of (DPSP) give in to their disorder and arrange their schedule around it. Individuals with DPSP are "night-owls". Their peak functional efficiency occurs in the evening hours. They do not feel sleepy until the early morning hours (3 to 6 AM). At this time, if they go to bed they have no difficulty falling asleep or staying asleep. They enjoy a normally structured sleep, and will not naturally wake up until midday (11 AM to 2 PM). This is because their daily sleep/wake rhythms (circadian rhythms) are delayed with respect to the normal day/night cycle. Many sufferers of DPSP attempt to adhere to the conventional day/night cycle. In doing so, they invariably suffer a sleep onset insomnia. They will also experience daytime sleepiness while they attempt to awaken and function against their internal clock early in the morning. This condition is not to be confused with individuals who behaviorally prefer or force themselves to stay up late or over sleep in the morning. Individuals who behaviorally alter their sleep/wake cycle are more akin to shift workers, artificially altering their external clock. In many respects, individuals with DPSP are constantly battling the same effects of internal/external clock incongruity as shift workers and individuals with jet lag except that these effects are due to a shift in the internal clock.

Advanced Sleep Phase Syndrome is probably a rarer entity than DPSP. In this disorder, the internal clock sleep phase is advanced to an earlier time with respect to the day/night cycle. Sufferers will experience sleepiness in the early evening hours and will awaken in the early morning hours. A key feature to both sleep phase syndromes is that, when left to its own timing, the sleep quality is normal. These individuals are the "larks", and probably adapt poorly to evening or night shift work.

Like the other circadian rhythm disorders (shift work and jet lag), the sleep phase syndromes are treatable through education, rigorous sleep hygiene and chronotherapy. Chronotherapy includes rigorous timing of bedtime, arise time, meal times, the timing of exposure to bright light, and some times the use of medications.