58. Gender differences in sleep

11 September 2010 at 17:17 | Posted in Circadian rhythm | 2 Comments
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I’ve earlier seen hints that there are differences in men’s and women’s sleep timing.  Now a new study confirms that and has also found differences in the quantity of melatonin secretion and in the daily temperature amplitude.

The study participants were normal sleepers:  28 women and 28 men, ages 18-30, matched in pairs for age, habitual bedtime, habitual wake time and MEQ-results.  Under strictly controlled conditions, so-called constant routine, their core body temperatures and melatonin levels were measured.

The women reached higher levels of melatonin in the blood.

The men had a greater amplitude in body temperature throughout the day and night.

The illustration shows the significant differences in sleep timing between women and men, on average.  In each of the 28 matched pairs of participants, significant differences were found between the women and the men with regard to the intervals

  • between DLMOn and bedtime,
  • between wake time and DLMOff, and
  • between temperature minimum and wake time.

The women were sleeping and waking at the same clock time, but at a later biological time than the men.

Abbreviations:

  • MEQ = the Morningness-Eveningness Questionnaire by Östberg and Horne
  • DLMOn = Dim Light Melatonin Onset
  • DLMOff = Dim Light Melatonin Offset (Here, based on blood level, not offset of synthesis.)

 

Reference:  Cain, Sean W., Christopher F. Dennison, Jamie M. Zeitzer, Aaron M. Guzik, Sat Bir S. Khalsa, Nayantara Santhi, Martin W. Schoen, Charles A. Czeisler and Jeanne F.  Duffy.  Sex Differences in Phase Angle of Entrainment and Melatonin Amplitude in Humans.  Journal of Biological Rhythms 2010 25: 288.  DOI: 10.1177/0748730410374943

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Next post: Coming soon

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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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xlii. Researchers mentioned here

13 June 2009 at 18:05 | Posted in Circadian rhythm | 6 Comments
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Several researchers have been mentioned / cited here, and there’ll surely be more.  They are listed below. 

Bjorvatn, Bjørn (in post vii.), is a sleep researcher at the University in Bergen, Norway, and a co-founder of Bergen Sleep Center.

Czeisler, Charles A. (in post xliii.) has been researching circadian rhythms for several decades.

Dagan, Yaron  (in post xxxviii.) in Israel, often publishing together with Judith Abadi, stated in 2001: “Certain sleep-wake schedule disorders (SWSDs) cannot be successfully managed clinically (…).  …we propose new medical terminology for such cases–SWSD disability. SWSD disability is an untreatable pathology of the circadian time structure…  It is imperative that physicians recognize the medical condition of SWSD disability in their patients and bring it to the notice of the public institutions responsible for vocational and social rehabilitation.”  In almost all of his papers, he emphasizes that people with circadian rhythm disorders often are misdiagnosed because physicians don’t know (enough) about such disorders.  Here is a case study (abstract) about a 14-year-old boy whose other diagnoses fell as soon as his sleep disorder was diagnosed.  It should perhaps be obvious that I appreciate Dagan’s work and his opinion. 

DeCoursey, Patricia (in post xix.), is the grand old, grand old of the field of chronobiology.  In 1960 she invented the Phase Response Curve when the “daily” activity rhythms of her flying squirrels, kept in constant darkness, responded to pulses of light exposure. The response varied according to the time of day — that is, the animals’ subjective “day” — when light was administered. When DeCoursey plotted all her data relating the quantity and direction (advance or delay) of phase-shift on a single curve, she created the PRC. It has since been a standard tool in the study of biological rhythms.

Dijk and Lockley (in post v.).  Derk-Jan Dijk and Steven W. Lockley often publish together.  Dijk, who studies the regulation of sleep and circadian rhythms in humans, is director of the Surrey Sleep Research Centre in the UK.  Lockley, Assistant Professor of Medicine, Harvard Medical School, and Associate Neuroscientist in Sleep Medicine, Brigham and Women’s Hospital in the USA, is particularly interested in the effects of light on the circadian pacemaker in humans.

Horne and Östberg (in post xxxviii.) published their Morningness-Eveningness Questionnaire (MEQ) in 1976.   It is based on O. Öquist’s 1970 thesis at the Department of Psychology, University of Göteborg, Sweden: ”Kartläggning av individuella dygnsrytmer”, “Charting Individual Circadian Rhythms”.  This marks the beginning of modern research into chronotypes.  Olov Östberg modified Öquist’s questionnaire and, together with J. A. (Jim) Horne, he published the MEQ (pmid 1027738, abstract ) which still is used and referred to in virtually all research on this topic. 

Roenneberg, Till (in post xxxvii. and in post xlvii.), professor at the University of Munich, is one of the best-known chronobiologists in Europe, having received international prizes for both his research and his teaching.  He has built up the Centre for Chronobiology at the Munich Medical School with its database on the sleep of over 50 000 Europeans.  In 2008 in India he collaborated with and directed a project in Mangalore chronotyping the south Indian population, with data covering nearly 75 000 participants.  Roenneberg’s work ranges from the cellular/molecular mechanisms of the circadian clock to the consequences of shift work and, as mentioned, huge surveys.

Thorpy, Michael J. (post xxxii.), board certified in sleep medicine, is a sleep researcher and a professor of clinical neurology at the Albert Einstein College of Medicine in New York.  He has held high office in the National Sleep Foundation and in the Sleep Section of the American Academy of Neurology.  Thorpy was for many years editor of The International Classification of Sleep Disorders: Diagnostic and Coding Manual (ICSD) and has been publishing books and articles since the 1980s.

Uchiyama, Makoto (in posts xxxviii. and xxvii.), professor at the Nihon University School of Medicine in Tokyo and managing editor of Sleep and Biological Rhythms, the official English language journal of the Japanese Society of Sleep Research (JSSR), is a prolific co-author of studies on sleep, particularly on DSPS and Non-24, often in cooperation with Masako Okawa, chair of the Asian Sleep Research Society. (ASRS).  This research field is very active in Japan, where study subjects often are people with these disorders.  In the west, in contrast, studies are more often done on healthy, normal people with results extrapolated to effects in people with the disorders.  The Japanese researchers have shown, for example, that the interval between the lowest core body temperature and spontaneous awakening is much longer in people with Non-24 and DSPS than the “about two hours” which is considered normal.

Zivkovic, Bora, aka “Coturnix (in posts xxxvii.xxxiii.xviii. and  xv.), should have had his PhD by now but the ideal job came along and his dissertation isn’t getting done.  He tells about that and about chronobiology and about lots more at ScienceBlogs

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Next:  xliii. Blindfolding the blind

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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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