58. Gender differences in sleep
11 September 2010 at 17:17 | Posted in Circadian rhythm | 2 CommentsTags: Circadian rhythm, Core body temperature, DLMO, Entrainment, Melatonin, MEQ
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 CommentsTags: Chronotype, Eveningness, MEQ, Morningness, Prevalence
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 |
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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:
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 CommentsTags: Chronotype, Circadian rhythm, Core body temperature, Cortisol, DLMO, DSPS, Eveningness, Jet lag, Melatonin, MEQ, Morningness, Shift work, Sleep architecture, Sleep deprivation

“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.
- 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.
- 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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