From Wikipedia, the free encyclopedia
Chronotype is an attribute of human beings
reflecting whether they are alert and prefer to be active early or
late in the day. The continuum is often referred to as
"morningness/eveningness" or "larks" and "owls" where morning people wake up
early and are most alert in the first part of the day, and evening
people are most alert in the late evening hours and prefer to go to
bed late. Chronotype is also referred to as circadian type, diurnal
preference or diurnal variation.
Humans are normally diurnal animals, active in the daytime. As
with most other diurnal animals, human activity-rest patterns are
endogenously controlled by circadian
Normal variation in chronotypes encompasses sleep/wake cycles
that are from about two hours earlier to about two hours later than
Extremes outside of this range can cause a person difficulty in
participating in normal work, school, and social activities. If a
person's "lark" or (more commonly) "owl" tendencies are strong and
intractable to the point of disallowing normal participation in
society, the person is considered to have a circadian rhythm sleep
The twentieth century saw greatly increased interest in and
research on all questions about sleep. Tremendous strides have been made in
molecular, neural and medical aspects of biological rhythmicity.
Physiology professor Nathaniel Kleitman's 1939 book
Sleep and Wakefulness, revised 1963,
summarized the existing knowledge of sleep, and it was he who
proposed the existence of a basic rest-activity cycle. Kleitman,
with his students including William C. Dement and Eugene
Aserinsky, continued his research throughout the 1900s.
O. Öquist’s 1970 thesis at the Department of Psychology,
University of Göteborg, Sweden, marks the beginning of modern
research into chronotypes, and is entitled Kartläggning av
individuella dygnsrytmer, or "Charting Individual Circadian
Rhythms". Olov Östberg modified Öquist’s questionnaire and in 1976,
together with J. A. (Jim) Horne, he published the Morningness -
Eveningness Questionnaire, MEQ, which
is still used and referred to in virtually all research on this
topic. A short version can be found online.
Researchers in many countries have worked on validating the MEQ
with regard to their local cultures. A revision of the scoring of
the MEQ as well as a component analysis was done by Jacques
Taillard et al. in 2004, working
in France with employed people over the age of 50. Previously the
MEQ had been validated only for subjects of university age.
Several other assessment tools have been developed: the
Circadian Type Inventory (Folkard 1987); the Composite Morningness
Questionnaire (Smith 1989); the Lark-Owl Chronotype Indicator, LOCI
(Roberts 1999); and the Munich Chronotype Questionnaire, MCTQ
(Roenneberg 2003). Some of these are designed with particular
situations in mind, such as shift work scheduling, travel fatigue and jet lag, athletic performance
or best timing of medical procedures.
Most people are neither evening nor morning types but lie
somewhere in between. Estimates vary, but up
to half are either morning or evening people. People who share a
chronotype, morningness or eveningness, have similar
activity-pattern timing: sleep, appetite, exercise, study etc.
Researchers in the field of chronobiology look for objective markers
by which to measure the chronotype spectrum.
- Horne and Östberg, 1976, found that morning types had a higher
daytime temperature with an earlier peak time than evening types
and that they went to sleep and awoke earlier, while no differences
in sleep lengths were found. They also note that age should be
considered in assessments of morningness and eveningness, noting
how a "bed time of 23:30 may be indicative of a Morning type within
a student population, but might be more related to an Evening type
in the 40-60 years age group" (Horne & Östberg, 1976,
- Clodoré et al., France, 1986, found
differences in alertness between morning and evening types after a
two hour sleep reduction.
- Gibertini et al., USA, 1999,
assessed blood levels of the hormone melatonin, finding that the melatonin
acrophase (the time at which the peak of a rhythm occurs)
was strongly related to circadian type, while amplitude was not.
They note that morning types evidence a more rapid decline in
melatonin levels after the peak than do evening types.
- Duffy et al., USA, 1999,
investigated "changes in the phase relationship between endogenous
circadian rhythms and the sleep-wake cycle," and found that while
evening types woke at a later clock hour than morning types,
morning types woke at a later circadian phase.
- Baehr et al., USA, 2000, found
that, in young adults, the daily body temperature minimum occurred
at about 4 in the morning for morning types but at about 6 in the
morning for evening types. This minimum occurred at approximately
the middle of the eight hour sleep period for morning types, but
closer to waking in evening types. Evening types had a lower
nocturnal temperature. The temperature minimum occurred about a
half hour earlier in women than in men. Similar results were found
by Mongrain et al. in Canada, 2004.
- Zavada et al., The Netherlands, 2005, show
that the exact hour of mid-sleep on free (non-work) days may be the
best marker for sleep-based assessments of chronotype; it
correlates well with such physiological markers as Dim-Light
Melatonin Onset (DLMO) and the minimum of the daily cortisol rhythm. The
researchers also state that each chronotype category "contains a
similar portion of short and long sleepers."
- Giampietro and Cavallera, Italy, 2006, refer
to many studies in their examination of the relationship among
chronotypes, personality and creative thinking.
- Paine et al., New Zealand, 2006,
conclude that "morningness/eveningness preference is largely
independent of ethnicity, gender, and socioeconomic position,
indicating that it is a stable characteristic that may be better
explained by endogenous factors."
- Chung et al., Taiwan, 2009,
studied sleep quality in shift-working nurses and found that "the
strongest predictor of sleep quality was morningness-eveningness
not the shift schedule or shift pattern," as "evening types working
on changing shifts had higher risk of poor sleep quality compared
to morning types."
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