Circadian Rhythm Disorders

Circadian rhythm disorders are disruptions of the natural biological cycles that control how people are attuned to night and day.

Most people function on a circadian rhythm of about 24 hours, which is controlled by the internal biological clock in the brain. Shifting into or out of daylight savings time, traveling across time zones (which can cause jet lag), or working at a job that involves late evening or nighttime work can affect the body's circadian rhythm. However, factors outside the body, especially bright light, help to set the internal clock to the day cycle or time schedule appropriate to where the person is.

In a person with a circadian rhythm disorder, the body is unable to maintain its normal rhythm. The natural sleep schedule changes so that the person is out of phase with day and night.

Advanced sleep phase syndrome is a circadian rhythm disorder in which people fall asleep earlier in the evening and wake up earlier in the morning than they would like; it is common among older people. In delayed sleep phase syndrome, people fall asleep later at night and wake up later in the morning.

Less commonly, older people can have such a severe circadian rhythm disorder that they seem to be on no schedule at all, falling asleep and waking up unpredictably. These changes may be caused by aging. Visual loss and changes in hormones and surroundings may also contribute.

Diagnosis and Treatment

A doctor diagnoses a circadian rhythm disorder by looking closely at the timing of a person's sleep. Good sleeping habits are essential to restoring desirable sleep schedules.

Bright light therapy, in which a person is exposed during the day to sunlight or bright light from special light sources, may reinforce the body's natural responses to light. Bright light therapy may be effective for advanced or delayed sleep phase syndrome. Usually, the bright light is used in the evening for an advanced sleep phase and in the morning for a delayed sleep phase.

Short-term treatment with a sleep aid may help reset the circadian rhythm. Melatonin taken an hour before a person's regularly scheduled sleep time may be effective for preventing jet lag, especially when traveling east across more than three time zones. Melatonin has also been used to establish regular sleep-wake cycles in people with unpredictable rhythms.