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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xxxviii. Eveningness vs. DSPS

10 November 2007 at 07:00 | Posted in Circadian rhythm | 4 Comments
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“Well, I don’t like getting up before seven either,

but I have to, and I do.”

Implication: and you can, too.

But, is that true?

The article on Wikipedia about Chronotypes, morningness/eveningness, reports what researchers know so far about these normal variations, which have been studied since about 1970 and are measured by the Horne-Östberg questionnaire, the MEQ, a short version of which can be found online at Bruce Logie’s interesting site.

 
It can be interesting to compare normal evening types with what we know about people with Delayed Sleep-Phase Syndrome.

 
Normal, healthy sleepers can be morning types (up to 25%), intermediate types (50% or more) or evening types (up to 25%). Any of them can be classified as long sleepers or short sleepers in normal distribution. They have normal “sleep architecture”, as do most people with DSPS. 
 
Normal night owls who are good sleepers:
 
  • like to sleep in and don’t like to go to bed early.
  • are more alert in the evening than just after awakening, as opposed to morning types.
  • can take a nap at 10 a.m. or noon after a night with less sleep than usual, while morning types generally don’t want a nap until 2 p.m. or later.
  • experience both Dim-Light Melatonin Onset (DLMO) and the minimum of the daily cortisol rhythm later (clock time) than morning types.

So far, it sounds like people with DSPS are evening types, as the properties above apply to both groups. However, normal evening types:

  • after starting a new routine requiring them, for example, to start work earlier than before, will adjust their sleep-wake schedules to the new times within a few days.
  • awaken spontaneously earlier in their circadian phase than morning people; that is, the interval between the low point of the body temperature and wake time is shortest in evening types. In people with DSPS, it’s notably much longer than average.

People with DSPS do not adjust to a new schedule easily, if at all.

CRSD [circadian rhythm sleep disorders] patients differ from night or morning type people … in the rigidity of their maladjusted biological clock. While “owls” and “larks” prefer morning or evening, they are flexible and can adjust to the demands of the environmental clock. CRSD patients, on the other hand, appear to be unable to change their clock by means of motivation or education,” according to Dagan, 2002 (PDF, page 3).
 
Or, as Wikipedia puts it: Attempting to force oneself through 9 – 5 life with DSPS has been compared to constantly living with 6 hours of jet lag.”
 
Uchiyama et al, 1999, found that people with DSPS do not evidence normal recovery sleep after sleep deprivation. They conclude that “[t]his suggests that DSPS may involve problems related to the homeostatic regulation of sleep after sleep deprivation.
 
Some of the characteristics of normal evening types may or may not also be characteristic of people with DSPS. If these points have been reported in the literature about DSPS, I haven’t seen them:
  • Evening types have a core body temperature which is a bit lower than average, both day and night. Is this also true for people with DSPS?
  • Evening types have a melatonin profile which declines much more slowly after midpoint, as compared with morning types. Is this also true for people with DSPS?
  • Evening types take a long time to “get going” after awakening. In relation to the timing of spontaneous awakening, the following points contribute to this for evening types, and possibly also for people with DSPS:
  • the timing of lowest body temperature,
  • the timing of the cortisol minimum,
  • the timing of melatonin offset, and
  • the slower decline of blood levels of melatonin.  

We have a disorder which, without treatment, forces us to fall asleep even later than evening types. Simply trying to enforce conventional sleep and wake times does not advance the circadian markers. It seems almost impossible to wake us much earlier than our pre-programmed wake time (as my siblings will attest). The disorder is chronic, changing little or not at all after the age of 20.  

When normal chronotypes shift their schedules, all the body’s rhythms catch up and are synchronized to each other within a few days. In DSPS, the dissynchrony may continue as long as the shifted, “unnatural” schedule lasts, even for years or decades, leading to physical and psychological disorders.

It’s clear that people with DSPS who (try to) work days, have much the same set of problems that many shift workers have, whether these always work nights or are on a rotating schedule. However, shift workers’ problems receive sympathy and understanding while people with DSPS are commonly stereotyped as undisciplined and lazy. Dagan again (PDF, page 7), on adolescents, points out that “[f]requently, the patients’ parents, teachers, doctors, or psychologists believe that the patients’ biological sleep-wake problem and the accompanying dysfunction at school are motivational or psychological in nature, a belief that during the years, the patients tend to adapt themselves. This attitude toward CRSD patients, to which [they have] been subjected since early childhood or adolescence, adds psychological distress to the practical difficulties of coping with life.”

Like normal people, we do adjust (entrain) to the earth’s 24-hour rotation, but, without treatment, we don’t “learn” to wake up at a conventional, early time of day.

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Next:  xxxix. Guest Blogger

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xxxiii. Owls of the World, Unite!

24 March 2007 at 12:57 | Posted in Circadian rhythm | 2 Comments
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In Denmark, Norway and possibly other countries ‘larks’ (early-risers) are called ‘A-people’ while ‘owls’ (late-risers) are ‘B-people’. Language is important in defining issues, so this terminology is unfortunate, I think, but it is well-established. Just the fact that there is a defining terminology in various languages is an admission that there is an issue. The common terms in English, larks for morningness and owls for eveningness, seem much less (de-)grading. 

 Danes are, in my experience, good organizers. In late December 2006, the B-Society, ‘B-samfundet’, went public and it now has nearly 4000 members and a newsletter in Danish. On its web page, its goals are defined in Danish and in English. [Update, June 2007: There’s now an international site in English: The B-Society.] There is a page for comments [now defunct, replaced by forum], which are appearing thick and fast in the Scandinavian languages as well as English and others; spam is also appearing, so something needs to be done about that.

The B-Society wants the world to please forget the archaic requirement for all work to be done while the sun is up and preferably just as soon as it’s up. When everyone must appear at work and school at the same time in the (early) morning, traffic jams result and up to half of the workers will not be performing at peak capacity for several hours yet. We’ve had electric light for well over a century, and it is past time to make some changes to everyone’s benefit.   

To quote the site (I’ve corrected their halting English some): “… it is unproductive for ‘owls’ dealing with knowledge, creativity and innovation to be at work at 8:00 a.m. without being present mentally, since their productivity peaks in the afternoon and in the evening. The different rhythms of people will generate a good bottom line in the innovation-driven society.”

One concrete project which may show some promise is awarding “certification” to employers who are friendly to “owls”, aka B-people. As they put it: “The B-Society is working with B-Certification of employers who accept and respect the working rhythm of ‘owls’. B-Certification will enable ‘owls’ to navigate in the labour market and find those workplaces that actually implement flexible working hours as well as show respect for and acceptance of the life and work rhythm of ‘owls’.
Now this is an idea whose time has come! The B-Society seems not to have heard of Delayed Sleep-Wake Syndrome (DSPS), only the eveningness of fairly normal “owls”. Yet achievement of their goals will obviously help us, too, as sleep deprivation is nasty for all of us. More power to them!
 
The chronobiologist “Coturnix” has a blog entry about the B-Society here. I borrowed his title.
And the remarkable photo of an attacking owl is the winner of National Wildlife’s 35th annual photography competition. Kim Steininger of Pennsylvania took the picture in Ontario, Canada, last winter. She noticed that one of the great gray owls was staring back at her. “I didn’t think anything of it until it started flying at me,” she says. Before getting out of the way, she captured this digital photo with a 500mm telephoto lens.

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Next:  xxxiv. Guest Blogger: Alan West

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xii. Circadian rhythm disorders

27 November 2005 at 11:14 | Posted in Circadian rhythm | 6 Comments
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There are a great many sleep disorders. I read recently that an official list of them had been pared down to about 70. Many have to do with not getting enough sleep, or getting sleep of poor quality by several criteria. Some have obvious causes, such as chronic pain, frequent stops in breathing etc.

My interest is in the timing of sleep as my sleep seems otherwise normal. As the experts put it, I have normal “sleep architecture”. (For a good, short explanation of sleep architecture — stages and brain waves — see this page from Feinberg School of Medicine at Northwestern University in the USA.)

Nearly all of us can reset our clocks daily, adjusting the various rhythms to 24 hours. As much as I’ve read about it, I’ve not found a good enough explanation for being able to adjust to 24 hours while not being able to adjust to sleeping midnight to eight or so.

I’m not immune to the light/dark cycle. I need to get up at noon. I fly 8 hours east or west, go through jet lag like anyone else and within days I need to get up at noon in the new location. This is built in. I’m not the only one. I’d just like to understand it better.

A Japanese paper (2004) suggests these possible mechanisms:

  • reduced sensitivity of the oscillator to photic entrainment,
  • an intrinsic period beyond the range of entrainment to the 24 hour day, and
  • abnormal coupling of the sleep/wake cycle to the circadian rhythm.

 

The least common and most debilitating circadian disorder is the one where body temperature, melatonin secretion, sleep and other rhythms vary several times a day, in and out of phase with one another, so called Irregular Sleep/Wake Disorder. This has been reported in humans who’ve been in accidents and had physical injuries to the hypothalamus. It’s also been provoked by surgery in lab animals.

One of the most rare disorders which occurs naturally is called Non-24. Sufferers simply(?) live on a 23, 25 or 26 hour cycle, getting up one hour later each day for example, thus coming in sync with the earth’s rotation every few weeks. Their rhythms are in sync internally, just not with the light/dark cycle outside. Most, but not all, of these people are blind. 

ASPS, Advanced Sleep-Phase Syndrome, is also rare. These people fall asleep and awaken much earlier than normal. The disorder runs in families, and an American family has been studied intensively the last few years. Research on their genetic mutation was published in 2001. “Detailed sequence studies of the candidate human gene, hPer2, in the affected family members, revealed a key change in a single amino acid — from serine to glycine — at position 662 in the hPer2 protein.” The alteration “occurred in the portion of the hPer2 protein that governed binding to an enzyme called casein kinase one-epsilon (CK1e ).” In animal models, this enzyme regulates “proteins involved in controlling the length of circadian rhythms.”

Now this is beyond me, but it would appear that these disorders may be genetically programmed. Though ASPS is rare, it seems reasonable that researchers start there, since one can compare the DNA of people who are related to one other.

DSPS, Delayed Sleep-Phase Syndrome, is a bit more common. Studies indicate that somewhat more than one in a thousand adults have DSPS (Japan 0.13%, Norway 0.17%). It runs less commonly in families, but it doesn’t seem unreasonable to guess that its cause may be similar to that of ASPS.
 
Clearly, anyone whose health cannot tolerate frequent forced awakening earlier than 10 a.m., will have few real choices in our society. Thus, hardcore (inflexible) DSPS must be considered a disability.

Another disorder which may be related to the others is Seasonal Affective Disorder, SAD. Sufferers are normal in summer, have problems of mood, weight gain etc. when days get shorter and can often be treated successfully by bright light therapy. It seems likely that they may have a mild form of ASPS or DSPS which is “treated” by morning/evening daylight when days are long.

Diurnal preference, spoken of as “morningness”, larks, and “eveningness”, owls, is also a subject of study, the field of chronobiology. This is, reasonably enough, connected to one’s circadian rhythms. However, it does not appear that ASPS is an extreme morningness chronotype nor DSPS an extreme eveningness chronotype. The internal relationships among the various rhythms do not place these conditions on a simple continuum.

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Next post:  xiii. DSPS-sleep

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