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Sleep Disorders

Keeping Time with Your Internal Clock - Circadian Rhythms

The circadian rhythm is the internal body clock regulating all the body's functions that cycle over a 24 to 25 hour time period. These rhythms are reset daily to match a 24 hour day by such factors as exposure to daylight and social cues, for example when we eat our meals.

Our internal body clocks play a major role in determining when we feel sleepy and when we are awake. Individuals who keep a regular sleep-wake schedule tend to awaken at about the same time every day. In fact for some people, this is so routine that they do not need an alarm clock to awaken in the morning.

Problems with Circadian Rhythms

Problems with the circadian rhythm arise when the internal rhythms become of out synch with the surrounding environment. This occurs in the setting of rotating shift work or rapid travel through time zones (jet lag). In addition, some individuals are programmed to go to bed early and wake up early ("morning larks") while others tend to stay awake until late into the night and like to sleep late into the day ("night owls"). Morning larks and night owls may experience problems when work or school requires them to be awake at a time when they would rather be sleeping.

Changing Circadian Rhythms

The internal clock can be advanced (moved forward so you are sleepy earlier in the evening) or delayed (moved backwards so you are more awake late into the night) by changing the timing of light exposure and other social cues. However, the internal clock can only be adjusted by 1-2 hours per day in either direction with these maneuvers. When individuals try to alter their rhythms by more than this, they tend to feel poorly with fatigue, sleepiness and nausea (as seen with jet lag, for example).

It often takes several days to fully adjust our circadian rhythms to a new schedule and thus going back and forth between schedules over the course of a few days can be difficult. This problem is often seen in those who perform rotating shift work. They feel chronically fatigued and tend to suffer from a lack of adequate sleep.

Delaying the Internal Clock

As most individuals normally have an internal rhythm that is slightly longer than the 24 hour day, it's easier to delay the biological clock as opposed to advance it. This can be accomplished by making changes such as excising in the evening, eating meals late in the evening, and getting bright light exposure in the late evening (sun light is usually best). Avoiding light exposure early in the morning will also help. As noted above, it may take several days before your brain and body adjust to a new schedule and it is best done gradually and not all at once.

In some cases, the appropriate use of melatonin or related medications may be useful, though this should only be done under the care of a physician with knowledge in this area.  The use of stimulants to help you delay your sleep schedule is complicated by side effects from the stimulants, and by the fact that they don't significantly alter the underlying circadian clock. The use of stimulants to delay the internal clock is generally not recommended.

Advancing the Internal Clock

Like delaying your internal clock, advancing your circadian rhythms (going to bed earlier and waking up earlier) can be achieved by behavioral modifications. Getting early morning light exposure, avoiding light exposure late in the day, eating meals earlier and avoiding late day exercise all can help with advancing the body's clock. This tends to be more difficult to do than delaying your clock, so patience and persistence may be needed.

The use of melatonin or other agents that might help with advancing the circadian rhythm should be done under the care of a physician.

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Last Reviewed: Mar 21, 2014

Dennis   Auckley, MD Dennis Auckley, MD
Associate Professor of Medicine
School of Medicine
Case Western Reserve University