Sleep Disorder, Shift Work
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- The human system relies on a circadian rhythm coordinated by the suprachiasmatic nucleus (SCN), an endogenous clock in the hypothalamus that links the nervous system to the endocrine system (1).
- A shift in work schedule can desynchronize this circadian pacemaker.
- The major environmental factor disrupting or resetting the circadian rhythm is light at night (LAN) (1).
- Shift work disorder (SWD), classified as a circadian rhythm sleep disorder, is caused by a misalignment between the internal circadian rhythm and the required sleep–wake schedule due to erratic or nighttime shift work (2).
- Diagnostic criteria for SWD require all criteria for circadian rhythm disorder in addition to:
- Criteria for circadian rhythm disorder:
- Persistent/recurrent sleep disruption due to either an alteration in the circadian (24-hour) timekeeping system or misalignment between endogenous circadian rhythm and exogenous factors that affect sleep
- Insomnia/excessive daytime sleepiness or both
- Impairment in occupational, educational, or social functioning
- Criteria for SWD:
- Insomnia/excessive sleepiness, accompanied by reduced sleep time, associated with a recurring work schedule that overlaps with the usual time for sleep
- Symptoms associated with shift work schedule are present for at least 3 months.
- Sleep log or actigraphy monitoring (with sleep diaries) for at least 14 days demonstrates disturbed sleep (insomnia) and circadian and sleep-time misalignment.
- Sleep disturbance is not due to another current sleep disorder, mental disorder, medical disorder, substance use disorder, or medication use.
- Criteria for circadian rhythm disorder:
- Shift work includes night shifts, evening shifts, or rotating shifts. Approximately 15–25% of the workforce in the United States are shift workers (2).
- SWD has been estimated to affect 10–23% of 22 million American shift workers, with a prevalence estimate of approximately 2–5% of the general population (14% night shift workers and 8% of rotating shift workers) (3).
- Circadian rhythms are present in multiple biologic functions, including body temperature, hormone levels, blood pressure, metabolism, cellular regeneration, sleep–wake cycles, and DNA transcription and translation (2).
- Transcription factors involved in circadian rhythms (the “molecular clock”) control production of many proteins expressed with a periodicity of approximately 24 hours. This molecular clock is self-sustaining and requires a daily reset or it may become out of sync with environmental cues (zeitgebers) (2).
- The most powerful zeitgeber (timekeeper) is light. Light transmitted from the retinohypothalamic tract of the eye to the SCN of the hypothalamus upregulates the production of the “clock gene” (PER) (2).
- Periods of darkness cause the SCN to induce melatonin release from the pineal gland, which can also help to reset the molecular clock (2).
- A dyssynchrony between the endogenous molecular clock and external cues (most notably light/dark cycles) is responsible for circadian rhythm disorders and can impact both physical and mental health (2).
- Shift work, including night shifts, early morning shifts, or rotating shifts
- Younger age and “eveningness” (a.k.a. “night owls”) may protect against the development of SWD (2).
No genetic predisposition has been described.
- Limit rotating shifts.
- Use bright light during shifts.
- Schedule brief (10- to 20-minute) naps during shifts, if possible.
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 (2).
- Shift workers also have a higher risk of vehicular accidents, job-related injuries, absenteeism, and quality control errors (2).
- SWD has been associated with gastrointestinal (GI) disease, specifically peptic ulcer disease, cardiovascular disease (CVD), ischemic stroke, infertility, mood disorders, and pregnancy complications (2,4).
- 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 (1).