Circadian rhythms influence body temperature, sleep and wakefulness and a variety of hormonal changes. Sunlight and other time cues help to set and maintain circadian cycles. Even without these time cues from the great outdoors, fluctuations in circadian rhythms would continue to occur within a period of about one day. Circadian rhythms are coordinated by small nuclei at the base of the brain, the suprachiasmatic nuclei (SCN). The SCN have connections with other parts of the brain to control the body's temperature, hormone release and other functions. A pathway runs from the eye to the SCN and light seems to play the largest role in setting the circadian "clock".  Blind people often report problems with circadian rhythms, since it is difficult for them to get the time cues needed to set their circadian rhythm. Other factors that may affect the SCN and the setting of the circadian clock include changes in body temperature and medications. Body temperature, for example, starts to rise during the later hours of sleep, just before waking up. This seems to promote a feeling of alertness upon awakening in the morning. In the evening, body temperatures decrease in preparation for sleep. A drop in temperature also occurs in most people between 12 and 4pm, which may explain why many people feels sleepy in the early afternoon. Although it has yet to be proven that changes in body temperature determine our sleep habits, there does appear to be a relationship between the two.

Disorders of Circadian Rhythm

Jet lag

The most commonly experienced problem with circadian rhythm is jet lag.  Jet lag occurs when a person travels across several time zones within a day or two. A typical flight across seas, often produces jet lag symptoms that can last for a week or more. These symptoms include daytime sleepiness, insomnia, indigestion, irritability and poor concentration. Some people adapt more quickly than others, depending on the number of the time zones involved. Another example of a jet lag scenario is a shift worker.  When changing back and forth to different sleep/ wake patterns, often a person experiences the same symptoms.

Tips for coping with jet lag and shift work

1. Allow extra time for adjustment during a trip or when switching to a new work schedule.

2. Depending upon the new time zone, a 20 to 30 minute nap at a specific time of day can be useful in overcoming the jet lag symptoms.

3. The occasional use of short-acting sleeping medications can help reduce the symptoms of the circadian rhythm disorder. Check with a healthcare provider before taking any medications and never mix sleeping pills with alcohol or a antihistamines. Keep in mind these are for temporary use only and the effectiveness may fade within a month's time.

Heredity & Circadian Rhythm Problems

An individual's circadian system seems to be affected by genetics. Age-related changes in the circadian system also appear to influence the natural rhythm and ability to respond to time cues. These factors can lead to a conflict between the body's sleep cues and the demands of society.  Scientists are just beginning to understand how the circadian system works and what can be done to improve our ability to cope with these problems.

Advanced sleep phase syndrome (ASPS)

Waking up and going to bed too early?  For most, sleepiness begins in the early afternoon and results in an early bed time.  When morning comes sufferers of ASPS often wake up too early and then aren't able to go back to sleep  ASPS is more common among older adults and has only recently been recognized as a significant medical problem.

Delayed sleep phase syndrome (DSPS)

Going to bed and waking up too late?  Some people find that they are not able to fall asleep until 2 or 3am, and that they then have trouble waking up in time for work or school. This problem can interfere with both daily performance at work and school. Few lifestyles allow for this kind of sleep/wake schedule and psychological stress is often a result.

Weakened Circadian Rhythms

Some people seem to have a nonexistent or weakened circadian cycle. They become sleepy after being awake only a few hours and then nap for a few hours. These napping sessions occur randomly throughout the day. The constant napping often ends up substituting for a full night's sleep.

Treatment for circadian phase disorders

1. An abnormal circadian rhythm can be a symptom of depression or of poor sleep habits. In these cases, a sleep specialist should be consulted.

2. Light therapy is being studied and used as a way to shift the circadian system and reset the body's clock. Properly timed exposure to bright lights may help advance the sleep cycle.

3. Chronotherapy is used to reset the circadian rhythm by slowing altering a persons sleep wake patter. The intended result is accomplished by making use of the natural twenty-four-hour rhythm, employing later and later bedtimes until the patient has reached the desired bed time.

4. Some researchers have explored the use of supplemental melatonin. Melatonin is a chemical that is naturally produced by the body to help induce sleep. Melatonin supplements have been advertised as sleep aids, however; studies have not shown that melatonin helps those with frequent shift changes. Questions about the safety and dosing have not been answered, and the F.D.A.C. considers melatonin experimental.