vi. The timing of sleep

22 November 2005 at 23:45 | Posted in Circadian rhythm | Leave a comment
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We have several circadian rhythms which are determined by our body clocks.  The most obvious of these is the sleep/wake cycle.  We can and do override nature’s signals – otherwise alarm clocks wouldn’t have been invented.  
 
We vary widely in our ability to live on a schedule different from the built-in one.  Some people seem to have little trouble adjusting to shift work; others prefer to avoid it at all costs.  Some people struggle with jet lag and even with the switch to or from Daylight Savings Time; others ask “What’s the big deal?”   
  
Have scientists done any research into these differences among us?  They’ve done a great deal of work explaining what adjustments the body has to accomplish in such situations, but I can’t find anything about why one person adjusts quickly and easily while another (of the same age) just simply can’t. 
 
In the presentation below I’m talking about adults who do adjust their body clocks to a 24-hour day and who have adequate sleep quality.  With thanks to Darren for helping me to reason along these lines, I think adults are of four types with regard to the timing of sleep:

1) Normally timed body clock, flexible.  Preferred wake-up time is about 7 a.m. and there’s no problem getting to sleep eight or so hours earlier.  While an afternoon or night shift might wreak havoc with social life, it is no big deal physically / mentally.

2) Normally timed body clock, inflexible.  Bedtime and wake-up as above but with as little variation as possible.  Attempts to work or live on another schedule have caused such physical and/or mental discomfort / illness that any pressure to try it again will be resisted.

3) Abnormally timed body clock, flexible.  Seven a.m. is an unfortunate time to have to get up, but with sufficient self-discipline the night before, it can be done.  No big deal, but some sort of freelance career, or an afternoon or night shift, might be preferable.

4) Abnormally timed body clock, inflexible.  Those who’ve been paying attention during this lesson now see where this is going.  A person whose biological rhythms say that waking up at around noon (or at around 3 a.m.) is the only way to stay healthy, is theoretically no worse off than number 2 above.  Just do it!  Just stick to the necessary bedtime of 4 a.m. (or 7 p.m.), sleep your eight hours and you’re fine.

These ‘Type 4’ individuals have ASPS or DSPS – I’ll get back to what the alphabet soup stands for.

When one of them works a day shift, the boss and the doctor are going to say, as mine have done:  “I believe that you are not willfully telling lies; I know you too well for that.  At the same time I cannot see how what you are telling me could be the case.  I know of no explanation, and I can’t imagine how you really feel.”

Well, of course, those are the generous comments.  I’ll leave the less generous ones to your imagination.

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Next post:  vii. Sleep and OTHER daily cycles

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