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Circadian Rhythm Sleep Disorders
Circadian rhythm sleep disorders occur when people’s internal sleep-wake schedule (clock) does not align with the earth’s cycle of darkness (night) and light (day).
Jet lag and shift work commonly disturb the usual rhythms of sleep and waking.
People cannot awaken or go to sleep when they need or want to.
Doctors base the diagnosis on symptoms, sometimes using information from a sleep log and sleep laboratory testing.
Good sleep habits and exposure to bright light can help people readjust their sleep-wake cycle.
Circadian means around ( circa ) the day ( dies ). Circadian rhythms are the regular changes in mental and physical states that occur in about a 24-hour period—a person’s internal clock. These rhythms are controlled by an area of the brain that is influenced by light (called the circadian pacemaker). After entering the eye, light stimulates cells in the back of the eye (retina) to send nerve impulses to this area. These impulses signal the brain to stop producing melatonin, a sleep-promoting hormone.
Normally, people vary in their sleep and wake times. Some (morning people or larks) prefer to sleep and wake early. Others (night people or owls) prefer to sleep and wake late. Such variations are not considered a disorder as long as people can do the following:
People with a circadian rhythm sleep disorder fall asleep at inappropriate times and then cannot sleep or wake up when they need or want to. Their sleep-wake cycle is disrupted.
Causes may be internal or external. Internal causes include damage to the brain (for example, due to brain infection (encephalitis), stroke, head injury, or Alzheimer disease) and insensitivity to the cycle of night and day.
External causes include the following:
Sleep-wake reversals are common among people who are hospitalized because they are often awakened during the night and because their eyes are not exposed to sunlight long enough during the day.
There are several types of circadian rhythm disorders.
Jet lag disorder is caused by rapid travel across more than two time zones.
Shift work disorder varies in severity depending on how often shifts change, how much they change, whether they make sleep and wake times earlier or later, how many consecutive nights are worked, and how long the shift lasts. Always working night or evening shifts and keeping the same bed times on days off is preferable. However, even then, daytime noise and light may interfere with sleep. Also, workers often shorten their sleep time and sleep at different times on days off to participate in social or family events.
Delayed sleep phase syndrome occurs when people consistently go to sleep and awaken late (for example, go to sleep at 3 am and wake up at 10 am or as late as 1 pm ). This syndrome is more common among adolescents and young adults. People with this syndrome cannot fall asleep earlier even if they try.
Advanced sleep phase syndrome occurs when people consistently go to bed and awaken early. It is more common among older people. People with this syndrome cannot stay awake until later times even if they try.
Non–24-hour sleep-wake syndrome occurs when the sleep-wake cycle changes every day. Sleep and wake times vary by 1 to 2 hours each day. This syndrome is much less common and tends to occur in blind people.
Because people cannot sleep when they need to, they may be sleepy during the day and have difficulty concentrating, thinking clearly, and doing their usual activities. They may misuse alcohol, sleep aids, and stimulants in an effort to sleep or stay awake.
Symptoms may be worse when people change their sleep schedule frequently, as when they frequently travel across several time zones or change their shift at work. Symptoms are also worse if the change makes wake and sleep times earlier (advances the sleep cycle) because delaying sleep is easier than going to sleep earlier. The sleep cycle is advanced when people fly east or when shifts change from days to nights to evenings.
If the cause is external, the timing of other circadian body rhythms, including temperature and hormone secretion, is affected. Thus, people may feel generally unwell, irritable, nauseated, and depressed, as well as sleepy. The risk of heart and metabolic disorders may also be increased.
If the cause of the disruption can be corrected, symptoms resolve over several days as rhythms readjust. In older people, resolution may take a few weeks or months.
Developing good sleep habits can help (see Sleep Hygiene).
Exposure of the eyes to bright light at appropriate times may be the most helpful strategy. Such exposure helps reset the internal clock. For example, travelers should spend time in sunlight, particularly in the morning, after they reach their destination (see Problems in Transit : Sleep Disturbance). Shift workers should spend time in bright light (sunlight or artificial light) at times when they should be awake. Wearing sunglasses on the way home from work reduces exposure to bright light before bedtime and may help. While shift workers are asleep, they should make the bedroom as dark and quiet as possible. Sleep masks and white-noise devices can be used. Exposure to bright light in the morning may help people with delayed sleep syndrome. Bright light in the evening may help people with advanced sleep syndrome.
Another strategy is to gradually shift the sleep-wake schedule to the one that is desired. Travelers may benefit from gradually shifting their schedule to approximate that of their destination, beginning well ahead of travel time.
If symptoms persist, sleep aids with effects that last only a short time (short-acting drugs) and drugs that stimulate the brain (such as modafinil) may help people sleep better and feel more alert during the day. However, these drugs do not adjust the body rhythms any faster.
Melatonin may help minimize the effects of jet lag and problems related to working shifts. However, its use is controversial. Melatonin appears to be safe for short-term use (up to a few weeks), but the effects of using it for a long time are unknown.
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