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CIRCADIAN RHYTHMS

Most biological and psychological processes vary according to a natural rhythm. Many of these variables (including sleep) have a cycle of about a day and are called circadian rhythms. Circadian rhythms influence body temperature, sleep and wakefulness, and a variety of hormonal changes. Sunlight and other time cues help to set circadian cycles so that they are consistent from day to day. Even if we didn't have time cues from the outside, fluctuations in circadian rhythms would continue to occur within a period of about one day. In most people, the naturally occurring circadian period is about 25 hours, slightly longer than a day! Some people find that their sleep/wake cycles cannot adjust to a 24-hour period, however hard they try. Bedtimes may be very irregular or continue to drift later and later, resulting in a variety of problems similar to those encountered with jet lag.

Circadian rhythms are coordinated by small centers at the base of the brain, the suprachiasmatic nuclei (SCN). This center has connections with other parts of the brain to control the body's temperature, hormone release, and many other functions. A pathway runs from the eye to the SCN, and light seems to play the largest role in setting the circadian clock. Interestingly, blind people often report problems with circadian rhythms, since it is difficult for them to get the time cues needed to set their circadian clocks. Other factors that may affect the SCN and the setting of the circadian clock include changes in body temperature and effects of a variety of medications.

In healthy people, the various circadian rhythms are "in tune" like the many instruments of an orchestra. Body temperature, for example, starts to rise during the last hours of sleep, just before waking up. This seems to promote a feeling of alertness in the morning. In the evening, body temperature decreases in preparation for sleep. A drop in temperature also occurs in most people between 2:00 and 4:00 p.m., which may explain why many people feel sleepy in the early afternoon. Although it has not been proven that changes in body temperature determine our sleep habits, there does appear to be a relationship between the two.

Disorders of circadian rhythms
Occasionally, certain circumstances or factors can cause the "circadian orchestra" to go out of sync.

Jet lag
The most widely experienced circadian problem is jet lag, which occurs when a person travels across several time zones. A typical flight from the United States to Europe, for example, often produces jet lag symptoms that can last for a week or longer. These include insomnia, daytime sleepiness, indigestion, irritability, and poor concentration. Some people require up to a week to adjust to new time cues; some adapt more quickly, depending on the number of time zones involved.

Circadian problems for shift workers
Shift workers are those who work nontraditional hours, such as night shifts or rotating shifts. These workers often face problems similar to jet lag without ever leaving home. People who work the night shift have to adjust to an unnatural schedule of working while others are sleeping and sleeping while others are awake. In addition, they may not get the same amount of sleep during the day as daytime workers do at night because of interruptions such as noise, sunlight, and increased room temperature.

People who work rotating shifts often find it difficult to get enough sleep, since their work schedules change frequently. Certain adjustments to the sleep schedule can help make this transition easier. On the last few days of the evening shift, workers should delay bedtimes and wake-up times by one to two hours. As the night shift begins, workers will already be well on the way to adapting to the new schedule.

Tips for coping with jet lag and shift work
1. Try to allow extra time for adjustment during a trip or when switching to a new work schedule. Don't skimp on time for resting.
2. Depending upon the new time zone, a short nap at a specific time of day can be useful in helping overcome jet lag.
3. The occasional use of a short-acting sleeping pill can help reduce the symptoms of circadian rhythm disorder. Check with a doctor before taking any medications, and never mix sleeping pills with alcohol or antihistamines.

It is generally not advisable to use a sleep aid for longer than three to four weeks, since the effectiveness wears off over time.

Delayed sleep phase syndrome (DSPS)
Some people find that they are not able to fall asleep until 2:00 or 3:00 a.m., and that they then have trouble waking up in time for work or school. Few lifestyles allow for this kind of sleep/wake schedule. This problem - which is more common in young adults than in other age group - can interfere with employment and school, and can lead to psychological stress.

Advanced sleep phase syndrome (ASPS)
This syndrome is more common among older adults, and has only recently been recognized as a significant problem. Sleepiness usually begins in the early afternoon, and sufferers often wake up too early and then aren't able to go back to sleep. Because ASPS usually doesn't interfere with working hours, society is more tolerant of this problem than of DSPS. ASPS becomes a problem, however, when sleepiness interferes with plans for evening business or social commitments. As in DSPS, lack of sleep does little to remedy this problem. ASPS suffers would continue to wake up early even if they forced themselves to stay awake until later in the evening.

Weak or nonexistent circadian rhythms
Some people seem to have weak or nonexistent circadian cycles. They become sleepy after being awake only a few hours, and then may nap for a few hours. These napping sessions occur at random throughout the day. For these people, brief naps substitute for a full night's sleep.

1. In some cases, an abnormal sleep cycle can be a symptom of depression or of poor sleep habits. Evaluation by a professional can lead to proper treatment. 2. Bright-light therapy is being studied 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 can be used to "rest" the circadian system. This technique makes use of the natural 25-hour rhythm, employing later and later bedtimes until the patient has rotated bedtime completely around the clock and the desired bedtime is reached. 4. Some researchers have explored the use of supplemental melatonin, a naturally occurring substance that increases in the bloodstream during the night. Although this form of treatment is experimental, it is believed to help promote sleep onset.

SLEEP HYGIENE
These guidelines can be helpful in alleviating all types of sleep disorders. These suggestions will help most people sleep well.

Get up about the same time every day.
Go to bed only when sleep
Establish relaxing pre - sleep rituals - such as a warm bath, light bedtime snack, or 10 minutes of reading.
Exercising regularly. Confine vigorous exercise to early hours, at least six hours before bedtime and do mild exercise - such a simple stretching or walking- at least four hours prior to bedtime.
Keep a regular schedule. Regular times for meals, medication, and other activities help keep the inner clock running smoothly.
Avoid ingestion of caffeine with six hours of bedtime. Don't drink alcohol, especially when sleepy. Even small does of alcohol can have a potent effect when combined with tiredness.
Avoid smoking close to bedtime.
Try to nap at the same time every day; mid afternoon is the best time for most people
Avoid sleeping pills, or use them conservatively. Most doctors avoid prescribing sleeping pills for periods longer than three weeks.

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