Circadian rhythm disorders are disruptions in a person's circadian rhythm -- a name given to the "internal body clock" that regulates the (approximately) 24-hour cycle of biological processes in animals and plants. The term circadian comes from Latin words that literally mean around the day. There are patterns of brain wave activity, hormone production, cell regeneration, and other biological activities linked to this 24-hour cycle.

The circadian "clock" in humans is located mainly in the suprachiasmatic nucleus (SCN), which is a group of cells located in the hypothalamus (a portion of the brain). Circadian rhythms are important in determining human sleeping patterns.

What Causes Circadian Rhythm Disorders?

Circadian rhythm disorders can be caused by many factors, including:

Shift work
Pregnancy
Time zone changes
Medications
Changes in routine

Common Circadian Rhythm Disorders

Jet Lag or Rapid Time Zone Change Syndrome: This syndrome consists of symptoms including excessive sleepiness and a lack of daytime alertness in people who travel across time zones.
Shift Work Sleep Disorder: This sleep disorder affects people who frequently rotate shifts or work at night
Delayed Sleep Phase Syndrome (DSPS): This is a disorder of sleep timing. People with DSPS tend to fall asleep at very late times and have difficulty waking up in time for work, school, or social engagements.
Advanced Sleep Phase Syndrome: Advanced sleep phase syndrome is a disorder in which the major sleep episode is advanced in relation to the desired clock time. This syndrome results in symptoms of evening sleepiness, an early sleep onset, and waking up earlier than desired.
Non 24-Hour Sleep Wake Disorder: Non 24-hour sleep wake disorder is a condition in which an individual has a normal sleep pattern but lives in a 25-hour day. Throughout time the person's sleep cycle will be affected by inconsistent insomnia that occurs at different times each night. People will sometimes fall asleep at a later time and wake up later, and sometimes fall asleep at an earlier time and wake up earlier.

How Are Circadian Rhythm Disorders Treated?

Circadian rhythm disorders are treated based on the kind of disorder diagnosed. The goal of treatment is to fit a persons sleep pattern into a schedule that can allow the person to meet the demands of a desired lifestyle. Therapy usually combines proper sleep hygiene techniques and external stimulus therapy such as bright light therapy or chronotherapy. Chronotherapy is a behavioral technique in which the bedtime is gradually and systematically adjusted until a desired bedtime is achieved. Bright light therapy is designed to reset a persons circadian rhythm to a desired pattern. When combined, these therapies may produce significant results in people with circadian rhythm disorders.

Reviewed by The Sleep Medicine Center at The Cleveland Clinic.

WebMD Medical Reference provided in collaboration with the Cleveland Clinic