Most people operate on a 24-hour biological clock that is synchronized with bodily hormone production and natural light and darkness. These 24-hour cycles are collectively known as the circadian rhythm, and they play a major role in our sleep cycle.
Circadian rhythm sleep disorders – formally known as circadian rhythm sleep-wake disorders – are a group of conditions tied to dysfunctions or misalignments with the body’s internal clock. Examples of these disorders include mild conditions such as jet lag, as well as more debilitating conditions such as delayed and advanced sleep-wake disorder, irregular sleep-wake rhythm disorder, and shift work disorder.
The circadian rhythm is crucial to different physiological processes. In addition to sleep, this rhythm helps regulate body temperature, eating and digestion, and hormonal activity. The master circadian clock is found in the hypothalamus of the brain and composed of a cluster of proteins known as the suprachiasmatic nucleus (SCN). In a healthy adult, this clock resets – or “entrains” – every 24 hours based on light and darkness cycles. A healthy person who wakes up in the morning will gradually become more tired throughout the day, and feelings of sleepiness will peak in the evening when it is dark out.
A person’s sleep rhythm changes and evolves with age. This is why teenagers often go to bed later than both younger children and adults. As we get older, we tend to go to bed and wake up at earlier times of the day.
According to the American Academy of Sleep Medicine (AASM) International Classification of Sleep Disorders, a circadian rhythm sleep-wake disorder occurs because of an alteration to the body’s internal timekeeping system, the clock’s inability to entrain roughly every 24 hours, or a misalignment between the clock and a person’s external environment.
While symptoms for these disorders can vary, most cause excessive daytime sleepiness. Insomnia – difficulty falling or staying asleep – is another common issue associated with these disorders.
A formal diagnosis of a circadian rhythm sleep-wake disorder involves specific criteria including:
As these criteria demonstrate, circadian rhythm sleep disorders can provoke significant health effects including problems in work or school as well as an elevated risk of vehicular or workplace accidents.
Based on AASM classifications, the separate types of circadian rhythm sleep-wake disorders include the following:
Delayed sleep-wake phase disorder occurs when a person’s sleep-wake cycle is pushed back more than two hours beyond what is considered a typical sleep schedule. A delayed circadian rhythm can cause people to struggle with falling asleep at night and waking up earlier in the morning. People with this condition often suffer from lack of sleep if they have school or work obligations that require an early wake-up time. Many people with this disorder are considered evening chronotypes, or night owls; its prevalence rate for young adults and adolescents is 7 to 16%.
Advanced sleep-wake phase disorder is essentially the opposite: the person tends to fall asleep and wake up more than two hours before their desired times. Advanced age is a major risk factor for this disorder.
In order to receive a diagnosis for delayed or advanced sleep-wake phase disorder, the patient must experience symptoms for at least three months. In addition, they must also report improvements to their sleep quality and duration if allowed to follow their own sleep schedule (rather than a schedule dictated by work or other obligations).
This disorder is characterized by inconsistent sleep patterns without a stable rhythm or entrainment to day-night cycles. Abnormal sleep periods can cause both difficulty sleeping and excessive daytime sleepiness during the course of the day. Most people with irregular sleep-wake rhythm disorder have neurodevelopmental or neurodegenerative disorder, such as Parkinson’s disease, Alzheimer’s disease, or Huntington’s Disease. The disorder has also been observed in children with developmental disabilities.
The fragmented sleep cycle of this disorder typically yields periods of sleep that last four hours or less. As a result, people with irregular sleep-wake rhythm disorder frequently nap throughout the day. Sleep fragmentation may be more severe for Alzheimer’s patients who experience sundowning, which involves restlessness, agitation, or confusion that coincide with sunset.
Also known as free-running disorder, non-24-hour sleep-wake rhythm disorder occurs when the internal clock does not reset every 24 hours. As a result, a person’s normal sleep period is constantly shifting, working its way around the clock over a period of days or weeks. Severity of symptoms often depends on the person’s schedule and whether their obligations conflict with their sleep cycle.
People with this condition may have insomnia symptoms and excessive daytime sleepiness when their sleep periods don’t match up with the schedule of their social and professional life. When their schedule aligns with sleep periods, a person with this condition experiences few, if any, sleep disturbances.
This disorder primarily affects people who are totally blind. The eyes of a totally blind person cannot transmit as many light signals to the brain, leading to confusion about the time of day. As a result, their internal clock is often unable to entrain on a 24-hour cycle. Between 50% and 80% of blind people report sleep disturbances, and experts estimate half of totally blind people have non-24-hour sleep-wake rhythm disorder. A diagnosis requires symptoms that persist for at least three months.
People whose jobs require them to work partly or completely at night often experience shiftwork disorder, which is characterized by insomnia and excessive daytime sleepiness. The term “shift-work” can apply to any shift that falls outside the traditional 9 a.m. to 5 p.m. schedule, but shift work disorder usually affects those who work late at night and/or early in the morning. Rotating shifts composed of daytime and nighttime hours can also lead to sleep disturbances and daytime grogginess.
Most people with shift work disorder lose between one and four hours of sleep for each 24-hour period, and adjusting to work once their shift begins can become increasingly difficult over time. This disorder can be particularly dangerous because it increases the risk of accidents either at their workplace or on the road during a late-night or early-morning commute.
People with this condition may also develop ulcers, and self-medicate with alcohol or drugs in order to get enough sleep. Estimates vary, but it’s believed as many as 38% of shift workers have this disorder. It is equally prevalent among the sexes and different racial groups.
Most people experience jet lag after flights that pass over multiple time zones. The condition, marked by temporary sleep disturbances and daytime fatigue, represents a transition period during which a person’s internal clock needs to synchronize with local time. Jet lag symptoms typically begin one to two days after the flight and can persist for up to a week or two.
Eastbound travel tends to produce more severe jet lag than westbound travel; northbound and southbound travel usually results in little to no jet lag unless the plane crosses two or more time zones. Additionally, the severity of symptoms often correlates to the number of time zones crossed; for many people, the body will require one day of adjustment for each time zone.
Jet lag is usually not a serious condition, but it can propel people into a downward spiral if they do not practice healthy sleep hygiene during this post-flight period. Persistent symptoms can lead to insomnia and other more serious sleep disorders.
Disorders in this category are usually tied to underlying health conditions. They resemble the other circadian rhythm sleep disorders listed above in terms of general symptoms, including insomnia and excessive daytime sleepiness, but patients do not meet the diagnostic criteria. These are rare cases that typically require tailored care from a doctor or sleep specialist.
Treatment of circadian rhythm sleep disorders depends on the patient’s specific diagnosis. Most treatments emphasize the importance of good sleep hygiene, a healthy sleep environment, and a consistent sleep-wake schedule. These factors can improve entrainment and reduce sleep deprivation for people with these disorders.
Circadian rhythm sleep disorder treatment may include melatonin supplements. These supplements should be prescribed by a doctor and administered at specific times to induce feelings of sleepiness. Properly timed melatonin doses can effectively reorient your circadian rhythm and entrainment schedule. Always consult with a doctor before taking melatonin to ensure you are healthy enough to do so.
Timed bright light exposure in the morning can aid people with delayed sleep-wake phase disorder, whereas the same exposure in the evening can be used to treat those with advanced sleep-wake phase disorder. This type of light therapy can encourage a healthy shift in circadian rhythm.
For people with shift work disorder, timed light exposure during their shift can be helpful. These patients can also benefit from a regimen of napping before work and moderate caffeine intake during their shift. Coping strategies for staying awake during their shift and sleeping during the day can also be effective. These strategies include avoiding bright light during the day, bright light exposure at work, and maintaining an optimal sleep environment. Melatonin supplements or hypnotics can serve as sleep aids during the day, but these are a temporary fix and will not correct circadian misalignment.