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Internal sleep clock

07/06/2005 10:51AM


I know I have a very strong circadian rhythm or internal sleep clock. If I go to sleep at 11pm, I get into the habit of waking up at 7am,which is fine. But on those occasions when I go to sleep later, at 1am or 2am for example, I automatically still wake up at 7am, when lots of other people seem to compensate and sleep for a longer time the next morning. (I feel awful with less than 8 hours sleep). Other than the obvious solution of just keeping the same bed time, what about those times when I can`t? Is there any way to `sleep in` when my body needs to but won`t?? Thanks


Your question is quite a testament to the power of circadian rhythms! As you have pointed out, our internal body clocks play a major role in determining when we feel sleepy and when we feel awake. Individuals on very regular sleep-wake schedules tend to awaken at the same time every day and for some individuals, this is so routine that they do not need an alarm clock to awaken in the morning. This becomes a problem when situations arise that place the internal rhythms out of synchrony with the environment (a classic example of this Jet Lag – see a previous Netwellness answer) or when the circadian rhythms make it difficult to obtain enough sleep following a late night, as in your situation.

The body’s circadian rhythms usually cycle over a 24 to 25 hour time period. These rhythms are reset daily to match a 24 hour day by factors such as exposure to daylight and social cues, for example when we eat our meals. 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 in either direction per day 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).

Furthermore, 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 persons who perform rotating shift work. They feel chronically fatigued and tend to suffer from a lack of adequate sleep.

If you wish to try to delay your circadian rhythms (allowing you to stay up later and hopefully sleep later), then evening exercise, late evening meals, and late evening bright light exposure may help. However, as noted above, it may take several days before your brain and body adjust to this new schedule. Taking sedatives at the end of a late night could also be considered to try and help you “sleep through” your usual wake up time, though this approach is generally not recommended due to the short acting nature of most of the sedatives commonly used these days as well as the potential for side effects, including feeling sleepy or fatigued the next day. Avoiding stimulants (for example caffeine) on nights you stay up late may help you to be able to sleep in.

You should discuss this issue with your primary care physician. Specific factors in your history may be useful in tailoring a strategy that might work for you. Referral to a Sleep Specialist in your area may also be helpful.

If you would like further information about circadian rhythms, sleep disorders or sleep itself, I recommend the American Academy of Sleep Medicine website.  In addition to information about sleep medicine, the website also contains a list of accredited Sleep Centers and may help you to locate one nearest you. Good Luck!

For more information:

Go to the Sleep Disorders health topic.