xlvii. Distribution of early and late types

7 November 2009 at 02:23 | Posted in Circadian rhythm | 7 Comments
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Distribution, early and late types

The illustration above is adapted from Till Roenneberg et al., the team who invented the Munich Chronotype Questionnaire, MCTQ.  The MCTQ is a modern version of the Morningness-eveningness Questionnaire, MEQ, and it is considered to give the best estimate of morningness and eveningness chronotypes.  They have chosen to consider sleep onset at 00:30 and 01:00 as “normal” for the adult population.  Their results are 46.5% early types, 28.5% normal types and 25% late types — as shown in this table:

According to the illustration from MCTQ Percentage of population

Chronotype sleep time    % SUM
       
   EARLY TYPE  EXTREME> 2.0 % 20.30 – 04.30 < 0.5     46.5 %
21.00 – 05.00 < 0.5
21.30 – 05.30 < 0.5
22.00 – 06.00    2.0
     
MODERATE13.0 % 22.30 – 06.30    3.5
23.00 – 07.00    9.5
     
SLIGHT31.5 % 23.30 – 07.30  14.5  
00.00 – 08.00  17.0
         
         
NORMAL TYPE 00.30 – 08.30  16.0     28.5 %
01.00 – 09.00  12.5
         
         
   LATE TYPE 

 

SLIGHT15.0 % 01.30 – 09.30    9.0        

 

 

    25.0 %

02.00 – 10.00    6.0
     
MODERATE6.5 % 02.30 – 10.30    4.0
03.00 – 11.00    2.5
     
EXTREME> 3.5 % 03.30 – 11.30    2.0
04.00 – 12.00    1.0
04.30 – 12.30    0.5
05.00 – 13.00 < 0.5
05.30 – 13.30 < 0.5
         
SUM         100.0 %

But isn’t 1 AM rather late at night to be considered a “normal” bedtime?  In my opinion, normal sleepy time would be no later than 11:30 PM, midnight and perhaps 12:30 AM. 

Using my own idea of what is normal, I’ve reconstructed the table to show these results:  15% early types, 47.5% normal types and 37.5% late types, as shown here:

In my opinion, based upon their figures:

percentage of population

Chronotype sleep time    % SUM
       
   EARLY TYPE  EXTREME< 1.0 % 20.30 – 04.30 < 0.5     15 %
21.00 – 05.00 < 0.5
21.30 – 05.30 < 0.5
     
MODERATE5.5 % 22.00 – 06.00    2.0
22.30 – 06.30    3.5
     
SLIGHT9.5 % 23.00 – 07.00    9.5
         
         
NORMAL TYPE 23.30 – 07.30  14.5       47.5 %
00.00 – 08.00  17.0
00.30 – 08.30  16.0
         
         
   LATE TYPE 

 

SLIGHT21.5 % 01.00 – 09.00  12.5        

 

 

 

    37.5 %

01.30 – 09.30    9.0
     
MODERATE10.0 % 02.00 – 10.00    6.0
02.30 – 10.30    4.0
     
EXTREME6.0 % 03.00 – 11.00    2.5
03.30 – 11.30    2.0
04.00 – 12.00    1.0
04.30 – 12.30    0.5
05.00 – 13.00 < 0.5
05.30 – 13.30 < 0.5
         
SUM         100.0 %

So I’ve also redone the figure at the top of this page to reflect my opinion of what is early and late: 

 Distribution, early and late types

What time do you think “normal types” go to sleep at night?

See the Roenneberg 2007 review: Epidemiology of the human circadian clock.  See also the 5th comment below for an UPDATE.

Posted by Delayed2Sleep (aka “D”).

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Next: Guest blogger:  Breann (again)

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7 Comments »

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  1. Over the past few years I’ve asked a lot of friends, as well as peers at work (I’m a programmer) what time they go to bed, and how much sleep they need, and my impression is that a “normal” bedtime is between 11:30pm-12:30am. What surprises me is that most people report getting between 6 and 7.5 hours of sleep per night, skewed toward the lower end of that. It explains how so many people can go to bed at midnight and still get into work by 9am. I wish I could do that! I go to bed around 2am and need over eight hours of sleep, and more often, closer to 9 hours.

    By the way, I don’t think that these people are sleep-deprived, even though so many newspaper articles claim that many of us are. They have intellectually demanding jobs and seem to be alert and performing well.

  2. Thanks for interesting comment, Tim. A couple of very large studies have shown that a huge percentage of adults in the USA self-report 7.5 hours. (And, as you may well have read, people with considerably longer as well as shorter sleep, live shorter lives than those who sleep near 7.5 hrs., with no causality suggested.)
    .
    People with DSPS and Non-24 do generally sleep 8-9+ hrs.
    .
    Sleep deprivation is tricky to define and measure. One clue is whether these 6-hr sleepers sleep longer on the weekends or not. If 6 hrs is enough, it should be enough 7 days/week. Thanks again.

  3. I’ve been reading up on DSPS because I think it’s what I have, but they always seem to cut off at 5-5:30AM for the most extreme version. When left to my own devices, my perfect bedtime is around 9 AM. Usually waking up around 3PM. Is that just an extra extreme case or something else altogether? I don’t know if I have the full syndrome or disorder, because I can function ok if I have to work a 9 to 5 job, but I end up needing naps after work because it’s hard to get to sleep at night, and I’d end up staying up all night on my days off\vacations. Luckily I rarely had to deal with that, I usually work jobs that allow me to come in the afternoon or overnights.

  4. Oh, yes, there are people who can’t get to sleep before 6 AM, 7 AM and later. There are 2 aspects to consider re severity. The first is late sleep onset but good sleep. The other is degree of flexibility. Even people with a normal sleep time of 11 PM to 7 AM may be more or less flexible about it. Some can work swing or nights with little problem, others may get sick and very miserable. It sounds to me like you have a severely delayed phase by nature, but that your timing is very flexible. Make sense?

  5. UPDATE: Someone wrote me to ask where I got the percentages in the chart at the very top of this post; they are not in the referenced 2007 review by Roenneberg. Here’s how to get a copy of that chart:
    .
    Go to http://www.euclock.org. In the top section “Chronotype”, choose your language. Fill out the MCTQ and, if you include your e-mail address, Roenneberg et co. will send you your result in a PDF including that chart. I’ve not been able to find the chart on the ‘net, though it may be there somewhere. Hope this works for anyone interested.

  6. I think the first chart’s definition of “normal” is ridiculous, at least for the US. it appears to have “normal” waking at 8:30 or 9:00 am. Don’t most jobs in the US start at 9am? Schools at 7:30 or 8? I haven’t yet met anyone who can teleport instantly from sleep to work so this idea of “normal” or “typical” seems remarkably out of sync with society.

    Now, maybe it is “normal” for people to go to bed at that time and so everyone is running a sleep deficit (as mentioned in another comment) but if people really couldn’t function that way, I’d think people would be adjusting their bedtimes more or society would shift working hours. Really an interesting question.

    I’d love to see a study or get info on where they take typical sleepers and delayed sleepers and give them shifted work schedules. Delayed sleepers can do great if they work from 11-7, for example, and sleep from 2am-10am. Give them a start time of 8 or 9am, waking at 7 or 8 and it’s chronic sleep deficit. What happens when you take “typical” sleepers of 11:30pm-7:30 am or whatever and make them go to work even earlier? Do they just go to bed earlier? Or can they not fall asleep till 11:30pm either and are chronically exhausted?

    Maybe someday there will be more acceptance of the charting you have above, with more flexible work hours for folks.

    Ok, that is All. Great blog!

  7. Thanks for the engaged comment and the good words about the blog! And, yes, maybe someday people (doctors first!) will acknowledge that Circadian Rhythm Disorders exist and that a great many people would benefit from more flexible work hours. Some day.


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