Shift work sleep disorder
Encyclopedia
Shift work sleep disorder (SWSD) is a circadian rhythm sleep disorder
characterized by insomnia and excessive sleepiness affecting people whose work hours are scheduled during the typical sleep period. There are numerous shift work
schedules, and they may be permanent, intermittent, or rotating; consequently, the manifestations of SWSD are quite variable.
and excessive sleepiness associated with working (and sleeping) at non-standard times. Total daily sleep time is usually shortened by several hours despite attempts to optimize the sleep environment. Sleepiness is manifest as a desire to nap, unintended dozing, impaired mental acuity, irritability, reduced performance, and accident proneness. Shift work is often combined with extended hours of duty, so fatigue can be a compounding factor. The symptoms coincide with the duration of shift work and usually remit with the adoption of a conventional sleep-wake schedule. The boundary between a “normal response” to the rigors of shift work and a diagnosable disorder is not sharp.
propensity for sleep and wake. In addition to circadian misalignment, attempted sleep at unusual times can be interrupted by noise, social obligations, and other factors. Finally, there is an inevitable degree of sleep deprivation associated with sudden transitions in sleep schedule. For example, a night worker who stays awake for 24 hours on the first night of a tour of duty is acutely sleep deprived by morning.
There have been many studies suggesting health risks associated with shift work. For example, a 2007 study led by the IARC (International Agency for Research on Cancer
) showed that shiftwork has been associated with cancer
. Other studies have reported that night workers have an increased incidence of heart disease, digestive disorders and menstrual irregularities. Because a formal diagnosis of SWSD was not typically made in these studies, it remains unclear whether the reported risks apply to the subset of shifttworkers who qualify for a diagnosis of SWSD or apply to all shiftworkers.
considerations.
Many night workers take naps during their breaks, and in some industries, planned napping at work (with facilities provided) is beginning to be accepted. A nap (if possible) before starting a night shift is a logical prophylactic measure. However, naps that are too long (over 20-30 minutes) may generate sleep inertia
, a groggy feeling after awakening that can impair performance. Therefore brief naps (10 to 30 minutes) are preferred to longer naps (over 30 minutes). Also, long naps may also interfere with the main sleep bout.
In the transportation industry, safety is a major concern, and mandated hours of service
rules attempt to enforce rest times.
is a hormone secreted by the pineal gland
for about 12 hours at night. Taking melatonin resets the body clock in the opposite direction from light exposure; that is, taking melatonin in the afternoon or evening may cause the clock to reset to an earlier time, while taking melatonin in the morning may cause the clock to reset to a later time. Melatonin has been shown to accelerate the adaptation of the circadian system to a night work schedule. Melatonin may benefit daytime sleep in night workers by an additional direct sleep promoting mechanism. In the US and Canada, melatonin is not classified as a drug; it is sold as a dietary supplement. Although it is not licensed by the FDA as a treatment for any disorder, there have been no serious side effects or complications reported to date.
is the most widely used alerting drug in the world and has been shown to improve alertness in simulated night work. Modafinil
and armodafinil
are non-amphetamine alerting drugs originally developed for the treatment narcolepsy that have been approved by the FDA (the US Food and Drug Administration
) for excessive sleepiness associated with SWSD.
Circadian rhythm sleep disorder
Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep...
characterized by insomnia and excessive sleepiness affecting people whose work hours are scheduled during the typical sleep period. There are numerous shift work
Shift work
Shift work is an employment practice designed to make use of the 24 hours of the clock. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts....
schedules, and they may be permanent, intermittent, or rotating; consequently, the manifestations of SWSD are quite variable.
Diagnosis
The primary symptoms of SWSD are insomniaInsomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
and excessive sleepiness associated with working (and sleeping) at non-standard times. Total daily sleep time is usually shortened by several hours despite attempts to optimize the sleep environment. Sleepiness is manifest as a desire to nap, unintended dozing, impaired mental acuity, irritability, reduced performance, and accident proneness. Shift work is often combined with extended hours of duty, so fatigue can be a compounding factor. The symptoms coincide with the duration of shift work and usually remit with the adoption of a conventional sleep-wake schedule. The boundary between a “normal response” to the rigors of shift work and a diagnosable disorder is not sharp.
Causes and co-morbidities
Insomnia and wake time sleepiness are related to misalignment between the timing of the non-standard wake/sleep schedule and the endogenous circadianCircadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
propensity for sleep and wake. In addition to circadian misalignment, attempted sleep at unusual times can be interrupted by noise, social obligations, and other factors. Finally, there is an inevitable degree of sleep deprivation associated with sudden transitions in sleep schedule. For example, a night worker who stays awake for 24 hours on the first night of a tour of duty is acutely sleep deprived by morning.
There have been many studies suggesting health risks associated with shift work. For example, a 2007 study led by the IARC (International Agency for Research on Cancer
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
) showed that shiftwork has been associated with cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
. Other studies have reported that night workers have an increased incidence of heart disease, digestive disorders and menstrual irregularities. Because a formal diagnosis of SWSD was not typically made in these studies, it remains unclear whether the reported risks apply to the subset of shifttworkers who qualify for a diagnosis of SWSD or apply to all shiftworkers.
Prescribed sleep/wake scheduling
Experts agree that there is no such thing as an "ideal" night work schedule, but some schedules may be better than others. For example, rotating shifts every two weeks in a forward (delaying) direction was found to be easier than rotation in a backward (advancing) direction. Gradual delays (“nudging” the circadian system about an hour per day) has been shown in a laboratory setting to maintain synchrony between sleep and the endogenous circadian rhythms, but this schedule is impractical for most real world settings. Some experts have advocated short runs (1 to 2 days) of night work with time for recovery; however, in the traditional heavy industries, longer (5 to 7 day) runs remain the rule. In the end, scheduling decisions usually involve maximizing leisure time, fairness in labor relations, etc. rather than chronobiologicalChronobiology
Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...
considerations.
Many night workers take naps during their breaks, and in some industries, planned napping at work (with facilities provided) is beginning to be accepted. A nap (if possible) before starting a night shift is a logical prophylactic measure. However, naps that are too long (over 20-30 minutes) may generate sleep inertia
Sleep inertia
Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. The impaired alertness may interfere with the ability to perform mental or physical tasks...
, a groggy feeling after awakening that can impair performance. Therefore brief naps (10 to 30 minutes) are preferred to longer naps (over 30 minutes). Also, long naps may also interfere with the main sleep bout.
In the transportation industry, safety is a major concern, and mandated hours of service
Hours of service
The hours of service are regulations issued by the Federal Motor Carrier Safety Administration governing the working hours of anyone operating a commercial motor vehicle in the United States for the purpose of "interstate commerce"— moving commercial goods from one U.S. state to another...
rules attempt to enforce rest times.
Bright light treatment
The light-dark cycle is the most important environmental time cue for entraining circadian rhythms of most species, including humans, and bright artificial light exposure has been developed as a method to improve circadian adaptation in night workers. The timing of bright light exposure is critical for its phase shifting effects. To maximize a delay of the body clock, bright light exposure should occur in the evening or first part of the night, and bright light should be avoided in the morning. Wearing dark welder's goggles (avoiding bright light) during the morning commute home from work can improve circadian adaptation, although this cannot be recommended to someone who is driving. For workers who want to use bright light therapy, appropriate fixtures of the type used to treat winter depression are readily available but patients need to be educated regarding their appropriate use, especially the issue of timing. Bright light treatment is not recommended for patients with light sensitivity or ocular disease.Melatonin treatment
MelatoninMelatonin
Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...
is a hormone secreted by the pineal gland
Pineal gland
The pineal gland is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions...
for about 12 hours at night. Taking melatonin resets the body clock in the opposite direction from light exposure; that is, taking melatonin in the afternoon or evening may cause the clock to reset to an earlier time, while taking melatonin in the morning may cause the clock to reset to a later time. Melatonin has been shown to accelerate the adaptation of the circadian system to a night work schedule. Melatonin may benefit daytime sleep in night workers by an additional direct sleep promoting mechanism. In the US and Canada, melatonin is not classified as a drug; it is sold as a dietary supplement. Although it is not licensed by the FDA as a treatment for any disorder, there have been no serious side effects or complications reported to date.
Medications that promote alertness
CaffeineCaffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
is the most widely used alerting drug in the world and has been shown to improve alertness in simulated night work. Modafinil
Modafinil
Modafinil is an analeptic drug manufactured by Cephalon, and is approved by the U.S. Food and Drug Administration for the treatment of narcolepsy, shift work sleep disorder, and excessive daytime sleepiness associated with obstructive sleep apnea...
and armodafinil
Armodafinil
Armodafinil is a stimulant-like drug produced by the pharmaceutical company Cephalon Inc., which was approved by the FDA on June 15, 2007...
are non-amphetamine alerting drugs originally developed for the treatment narcolepsy that have been approved by the FDA (the US Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
) for excessive sleepiness associated with SWSD.