The Stanford Center for Sleep Sciences and Medicine

Shift Work and Circadian Rhythm Disorders

Returning Rhythm to your Sleep

The human body has an internal clock that regulates when we sleep, permitting sleep at night and helping us maintain wakefulness during daylight. This clock works best when we maintain regular routines, most importantly when we wake up, and when we have adequate exposure to daylight. The clock cycles around 24 hours (about a day). This is why it is called a circadian rhythm (circa means about and diem means day).

Sometimes the rhythm gets disrupted, whether it’s from an internal change to your clock or the result of working night-time shifts or the rhythm becomes out of sync with the external clock due to jet lag.

What is Circadian Rhythm Disorder?

A circadian rhythm disorder occurs when the internal clock regulating sleep and wakefulness is weakened or when it is misaligned with a person’s desired sleep period. Sleep specialists use a diagnostic system called the International Classification of Sleep Disorders (ICSD). The diagnostic category is established by a panel of experts who take into account available research and clinical experience. The current version of the diagnostic system include nine different circadian rhythm disorders, the most common of which are delayed sleep phase, advanced sleep phase, and shift work that are discussed below.

The Stanford Sleep Medicine Center helps people who suffer from circadian rhythm disorders sleep better at the times they wish to sleep and be more productive when they wish to be awake. An important component of treatment is helping patients sync their internal clocks with their desired sleep-wake schedules.

Read more about Circadian Rhythm Disorders:

Delayed Sleep Phase Syndrome | Advanced Sleep Phase Syndrome
Shift Work Sleep Disorder

Delayed Sleep Phase Syndrome

Delayed Sleep Phase Syndrome is a disorder in which the timing of sleep and the peak period of alertness are delayed several hours relative to societal clock. People with Delayed Sleep Phase Syndrome generally have difficulty falling asleep unless they go to bed very late (usually some hours after midnight) because their internal clock is sending alerting signals until late into the night, and have difficulty waking up at what is considered a “normal” time in the morning, because their internal clock is not yet producing strong alerting signals. Unless other sleep disorders, such a sleep apnea or insomnia, are present, an individual with Delayed Sleep Phase Syndrome sleeps well (in terms of duration and quality) when going to bed and waking up late but the syndrome makes it difficult to wake up in time for a typical school or work day. People are not considered to have a delayed sleep phase disorder unless they also experience impairment in social, occupational or other areas of their life as a result of their sleep disorder.

The prevalence of Delayed Sleep Phase Syndrome in the general population is unknown although the prevalence rate among adolescents and young adults is approximately 7-16%. The syndrome may develop in early childhood but most commonly it emerges or exacerbated during adolescence. Some adolescents delay their sleep schedules for social reasons and may not have underlying abnormalities in their circadian rhythm. For those, sleep schedules normalize in early adulthood.

Treating Delayed Sleep Phase Syndrome

Those suffering from Delayed Sleep Phase Syndrome often only seek the help of a sleep specialist after they’ve unsuccessfully tried to change their sleep schedule on their own. Sleep specialists use two particular treatment methods to help patients with this syndrome: Light Therapy and Chronotherapy.

Light Therapy
This technique uses appropriately timed exposure to light. The source of light could be artificial, such as a full spectrum lamp at 10,000 lux or portable visor at lower light intensity or, when reliably available at the right time, natural outdoor light. Longer properly timed light exposure is better, with recommended exposure duration of 30–90 minutes. The ideal timing of the light exposure depends on the best approximation available of the person’s circadian clock. The sleep specialists works with the patient to decide on the timing of the light exposure based on patient’s symptoms and life circumstances. The specialist may start by recommending light exposure take place shortly before the patient’s usual time of spontaneous awakening. The specialist helps the patient slowly shift the sleep period to an earlier time. After the desired sleep schedule is attained patients should maintain a fixed rise time (even on weekends and vacations) and ideally continue to use morning light exposure on most mornings, though the duration of light exposure can be shorter. Specialists often recommend using dim lights in the evening in conjunction with bright light exposure in the morning during the advancement of the sleep schedule.

To read more about bright light therapy, visit the Treatments Section.

Chronotherapy
This technique aims to reset the circadian clock by slowly delaying the bedtime (and hence the sleep period) by about two hours every few days. This strategy is used less commonly than the light therapy method. It invariably disrupts normal schedule of activity during the shift, when day and night are reversed.

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Advanced Sleep Phase Syndrome

Advanced Sleep Phase Syndrome is a disorder in which the timing of sleep and the peak period of alertness are advanced several hours relative to societal clock. People with Advanced Sleep Phase Syndrome generally have difficulty staying awake unless they go to bed very early because their internal clock is already at a relatively quiet state, and wake up very early, at what is considered a “normal” time in the morning, unable to fall back asleep, because their internal clock is already producing strong alerting signals. Unless other sleep disorders, such a sleep apnea or insomnia, are present, an individual with Advanced Sleep Phase Syndrome sleeps well (in terms of duration and quality) when going to bed and waking up early but the syndrome makes it difficult to stay awake in the evening and be engaged in social activities. Sleep quality is not impaired by the syndrome but afflicted individuals may have short sleep duration if they delay their bedtime. Nonetheless people with Advanced Sleep Phase Syndrome do not report that the syndrome affects their daytime work or school activities. Their most common complaint is that their evening activities are cut short by the need to sleep much earlier than what is considered the norm. This can affect family and social relationships. Individuals with Advanced Sleep Phase Syndrome should be cautious about driving in the late afternoon and evening, because they may be too drowsy. They also do not adjust well to evening or night shifts.

The prevalence of Advanced Sleep Phase Syndrome in the general population is unknown although it is most prevalent among older adults. Advanced Sleep Phase Syndrome has the same prevalence among men and women. Researchers have also found a strong genetic link: 40%-50% of people suffering from Advanced Sleep Phase Syndrome are related to someone who has the syndrome.

Treating Advanced Sleep Phase Syndrome

Most people don't seek treatment unless it starts to significantly impact their social life. Sleep specialists treat Advanced Sleep Phase Syndrome with evening bright light exposure (Bright Light Therapy). This helps delay the patient’s biological clock. The source of light could be artificial, such as a full spectrum lamp at 10,000 lux or portable visor at lower light intensity or, when reliably available at the right time, natural outdoor light. Longer properly timed light exposure is better, with recommended exposure duration of 30–90 minutes. The ideal timing of the light exposure depends on the best approximation available of the person’s circadian clock. The sleep specialists works with the patient to decide on the timing of the light exposure based on patient’s symptoms and life circumstances. There aren’t as much data about the effectiveness of light therapy for Advanced Sleep Phase Syndrome as there are for morning light exposure in delayed Sleep Phase Syndrome. One Australian study found good results with 4 hours of evening light exposure.

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Shift Work Sleep Disorder

Shift Work Sleep Disorder is a circadian sleep disorder in which a person experiences a constant or recurrent pattern of sleep interruption due to shift work schedule, resulting in difficulties initiating and maintaining sleep and/or excessive sleepiness when awake. Other symptoms of Shift Work Sleep Disorder include difficulty concentrating, headaches, and low energy. Non-traditional shifts, particularly rotating shifts, force people to place their sleep window at a time that is not congruent with their underlying circadian clock. Rotating shifts also weaken the signals from the internal clock leading to greater difficulties with sleep and sleepiness. As a result, people with Shift Work Sleep Disorder may have trouble staying alert at their work shift and feel their sleep is unrefreshing.

Treating Shift Work Sleep Disorder

Managing Shift Work Sleep Disorder is inherently difficult. Research is showing that some shift work schedules are better than others, but shift workers do not always have a choice. Improving the sleep of a shift worker with sleep difficulties requires understanding how the circadian clock works and finding pragmatic solutions to help people keep as strong of a circadian rhythm as is feasible under these unnatural work conditions. Adjusting the internal clock to adapt to a night-time may include properly timed bright and dim light exposures relative to the timing of the sleep window. For example, an individual whose shift ends in the morning who intends to go home and sleep should minimize exposure to light between the end of work and bedtime (e.g., wear sunshade, have blackout shades).

Shift work is often combined with a longer than 8 hour work schedule. As a result, shift workers tend to sleep less than day workers and become more sleep-deprived over several days and therefore need to be cautious when driving and when in environments in which dozing off is dangerous. Sleep specialists can often help shift workers maintain alertness by offering alerting medication or counter fatigue behavioral recommendations. Workers with irregular or rotating shifts are at particularly high risk for accidents and their sleep problem is harder to manage. Young adults and people who describe themselves as “night owls” appear to find it easier to adjust to night and non-traditional work shifts.

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