Jet lag and shift work commonly disturb the usual rhythms of sleep and waking.
People who have a circadian rhythm sleep disorder cannot awaken or go to sleep at normal hours.
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 initially after waking can help people readjust their sleep-wake cycle.
(See also Overview of Sleep.)
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 hormone that promotes sleep.
Normally, people vary in their sleep and wake times. Some people (morning people or larks) prefer to go to sleep and wake early. Others (night people or owls) prefer to go 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 go to sleep or wake up when they need or want to. Their sleep-wake cycle is disrupted.
Causes of circadian rhythm sleep disorders may be internal or external.
Internal causes include the following:
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
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 disorder 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 delayed sleep phase disorder cannot fall asleep earlier even if they try.
Advanced sleep phase disorder occurs when people consistently fall asleep and awaken early and cannot change this pattern. It is more common among older people. People with advanced sleep phase disorder 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. The length of the sleep-wake cycle remains the same, but it is more than 24 hours. Thus, sleep and wake times are delayed 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 of circadian rhythm sleep disorders 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.
Changes in Behavior to Improve Sleep
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, to minimize jet lag, travelers should spend time in sunlight, particularly in the morning, after they reach their destination. 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 shift workers fall asleep more easily after arriving home. 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 disorder. Bright light in the evening may help people with advanced sleep disorder.
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) may help people with insomnia sleep better, and drugs that stimulate the brain (such as modafinil) may help people feel more alert during the day, or, for people with shift work disorder, during their awake time. 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.
Tasimelteon acts like melatonin. It can help people who are totally blind and have non–24-hour sleep-wake syndrome by increasing nighttime sleep time and decreasing daytime sleep time. This drug is taken by mouth before bedtime at the same time every night. The most common side effects are headaches and abnormal dreams or nightmares.