Sleep Disorder, Shift Work

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Basics

Description

Shift work disorder (SWD), classified as a circadian rhythm sleep-wake disorder, is characterized by excessive sleepiness during desired waking period and/or insomnia during desired sleeping period. SWD is caused by a misalignment between the internal circadian rhythm and the required sleep-wake schedule defined by nontraditional work shifts including night shifts, afternoon or evening shifts, early morning shifts, irregular shifts, and rotating shifts (1).

Epidemiology

Prevalence
  • In the United States, approximately 20% of employed adults are shift workers (1).
  • SWD has an estimated prevalence of approximately 2–5% in the general population of the United States (1).
  • Shift work is often seen in service related occupations such as health care, protective services such as law enforcement and fire safety, transportation, and food services (1).

Etiology and Pathophysiology

  • Sleep disturbances in shift workers are explained by disruptions in two biologic processes. The homeostatic sleep drive and circadian rhythm of alertness interact with each other to regulate sleep. The homeostatic sleep drive increases with wakefulness and decreases with sleep. Alertness is regulated by the suprachiasmatic nucleus of the anterior hypothalamus and promotes wakefulness during the daytime and sleep at night. As homeostatic sleep drive increases during the day, the circadian rhythm of alertness increases and vice versa (1),(2).
  • Circadian rhythms play a role multiple biologic functions, including regulation of body temperature, hormone levels, blood pressure, metabolism, cellular regeneration, sleep-wake cycles, and DNA transcription and translation (3). This internal biologic clock fluctuates with 24-hour cycles and is primarily regulated by external and environmental cues (2).
  • The strongest influence on circadian rhythm is light. Light entering the eyes stimulates the retinohypothalamic and retino-geniculo-hypothalamic pathways to the SCN of the hypothalamus, subsequently suppressing melatonin from the pineal gland. During the day, melatonin levels are low, and the circadian rhythm of alertness is high (1).
  • Periods of darkness cause the SCN to induce melatonin release from the pineal gland, which can also help to reset the molecular clock (3).
  • In shift workers, there is a misalignment between one’s endogenous circadian rhythm of sleep and wakefulness and a sleep-wake schedule based on nontraditional shift work. Dyssynchrony results in excessive sleepiness during the work shift and/or insomnia during desired sleep time (1),(2),(3).

Genetics
Not all shift workers experience SWD, and there is variability in symptoms occurring among shifts workers with SWD. One possibly genetically linked trait is a person’s preference for the morning versus the evening. This is partially linked to the polymorphism of the PER3 “clock” gene involved in sleep-wake regulation (1).

Risk Factors

  • Older age may increase risk of development of SWD. Insomnia increases with age, and older adults may prefer the morning, increasing their risk for SWD (1).
  • Female shift workers reportedly have more symptoms of sleep loss, excessive sleepiness, and psychological distress relative to men. However, more studies are needed because it is unclear whether such differences exist due to other factors such as job type or home responsibilities (1).

General Prevention

  • Reduce or eliminate shift work.
  • Try to rotate shifts forward if shifts must be rotated.
  • Use bright light during shifts.
  • Improve sleep hygiene.
  • Schedule regular sleep including naps (<1 hour) just before a shift or, if possible, during a shift.

Commonly Associated Conditions

  • Shift workers often have impaired immediate free recall, decreased processing speed, and selective attention impairments that may worsen with longer duration of shift work (3).
  • Shift workers also have a higher risk of vehicular accidents, job-related injuries, absenteeism, and quality control errors (3).
  • SWD has been associated with gastrointestinal (GI) disease, specifically peptic ulcer disease, cardiovascular disease (CVD), ischemic stroke, infertility, pregnancy complications, mood disorders, and substance use disorders (3),(4). SWD has also been associated with obesity, diabetes, and metabolic disorders (1),(2).
  • There is also a possible increased risk of breast and prostate cancer. The International Agency for Research on Cancer (IARC) has classified shift work involving a circadian disruption as a probable carcinogen (5).

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Basics

Description

Shift work disorder (SWD), classified as a circadian rhythm sleep-wake disorder, is characterized by excessive sleepiness during desired waking period and/or insomnia during desired sleeping period. SWD is caused by a misalignment between the internal circadian rhythm and the required sleep-wake schedule defined by nontraditional work shifts including night shifts, afternoon or evening shifts, early morning shifts, irregular shifts, and rotating shifts (1).

Epidemiology

Prevalence
  • In the United States, approximately 20% of employed adults are shift workers (1).
  • SWD has an estimated prevalence of approximately 2–5% in the general population of the United States (1).
  • Shift work is often seen in service related occupations such as health care, protective services such as law enforcement and fire safety, transportation, and food services (1).

Etiology and Pathophysiology

  • Sleep disturbances in shift workers are explained by disruptions in two biologic processes. The homeostatic sleep drive and circadian rhythm of alertness interact with each other to regulate sleep. The homeostatic sleep drive increases with wakefulness and decreases with sleep. Alertness is regulated by the suprachiasmatic nucleus of the anterior hypothalamus and promotes wakefulness during the daytime and sleep at night. As homeostatic sleep drive increases during the day, the circadian rhythm of alertness increases and vice versa (1),(2).
  • Circadian rhythms play a role multiple biologic functions, including regulation of body temperature, hormone levels, blood pressure, metabolism, cellular regeneration, sleep-wake cycles, and DNA transcription and translation (3). This internal biologic clock fluctuates with 24-hour cycles and is primarily regulated by external and environmental cues (2).
  • The strongest influence on circadian rhythm is light. Light entering the eyes stimulates the retinohypothalamic and retino-geniculo-hypothalamic pathways to the SCN of the hypothalamus, subsequently suppressing melatonin from the pineal gland. During the day, melatonin levels are low, and the circadian rhythm of alertness is high (1).
  • Periods of darkness cause the SCN to induce melatonin release from the pineal gland, which can also help to reset the molecular clock (3).
  • In shift workers, there is a misalignment between one’s endogenous circadian rhythm of sleep and wakefulness and a sleep-wake schedule based on nontraditional shift work. Dyssynchrony results in excessive sleepiness during the work shift and/or insomnia during desired sleep time (1),(2),(3).

Genetics
Not all shift workers experience SWD, and there is variability in symptoms occurring among shifts workers with SWD. One possibly genetically linked trait is a person’s preference for the morning versus the evening. This is partially linked to the polymorphism of the PER3 “clock” gene involved in sleep-wake regulation (1).

Risk Factors

  • Older age may increase risk of development of SWD. Insomnia increases with age, and older adults may prefer the morning, increasing their risk for SWD (1).
  • Female shift workers reportedly have more symptoms of sleep loss, excessive sleepiness, and psychological distress relative to men. However, more studies are needed because it is unclear whether such differences exist due to other factors such as job type or home responsibilities (1).

General Prevention

  • Reduce or eliminate shift work.
  • Try to rotate shifts forward if shifts must be rotated.
  • Use bright light during shifts.
  • Improve sleep hygiene.
  • Schedule regular sleep including naps (<1 hour) just before a shift or, if possible, during a shift.

Commonly Associated Conditions

  • Shift workers often have impaired immediate free recall, decreased processing speed, and selective attention impairments that may worsen with longer duration of shift work (3).
  • Shift workers also have a higher risk of vehicular accidents, job-related injuries, absenteeism, and quality control errors (3).
  • SWD has been associated with gastrointestinal (GI) disease, specifically peptic ulcer disease, cardiovascular disease (CVD), ischemic stroke, infertility, pregnancy complications, mood disorders, and substance use disorders (3),(4). SWD has also been associated with obesity, diabetes, and metabolic disorders (1),(2).
  • There is also a possible increased risk of breast and prostate cancer. The International Agency for Research on Cancer (IARC) has classified shift work involving a circadian disruption as a probable carcinogen (5).

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