Chronotype
Encyclopedia
Chronotype is an attribute of animal
s, including human beings, reflecting at what time of the day their physical functions (hormone level, body temperature, cognitive faculties, eating and sleeping) are active, change or reach a certain level. This phenomenon is commonly reduced to sleeping habits only, referring to people as "larks
" and "owls
" which refer to, respectively, morning people (those who wake up early and are most alert in the first part of the day) and evening people (those who 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 creatures, that is to say they are active in the daytime. As with most other diurnal animals, human activity-rest patterns are endogenous
ly controlled by circadian rhythm
s.
Normal variation in chronotypes encompasses sleep/wake cycles that are from about two hours earlier to about two hours later than average. 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 disorder
.
. 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.
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 Scale of Morningness (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.
look for objective markers by which to measure the chronotype spectrum.
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, including human beings, reflecting at what time of the day their physical functions (hormone level, body temperature, cognitive faculties, eating and sleeping) are active, change or reach a certain level. This phenomenon is commonly reduced to sleeping habits only, referring to people as "larks
Lark (person)
Lark is a term used to describe a person who usually gets up early in the morning and goes to bed early in the evening. Other terms are "morning person" and "early bird"....
" and "owls
Night owl (person)
Night owl is a term used to describe a person who tends to stay up until late at night. Another name for a night owl is evening person.The opposite of a night owl is an early bird, a lark as opposed to owl, someone who tends to begin sleeping at a time that is considered early and also wakes early...
" which refer to, respectively, morning people (those who wake up early and are most alert in the first part of the day) and evening people (those who 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 creatures, that is to say they are active in the daytime. As with most other diurnal animals, human activity-rest patterns are endogenous
Endogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
ly controlled by circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...
s.
Normal variation in chronotypes encompasses sleep/wake cycles that are from about two hours earlier to about two hours later than average. 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 disorder
Circadian rhythm sleep disorder
Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep...
.
History
The 20th century saw greatly increased interest in and research on all questions about sleepSleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
. Tremendous strides have been made in molecular, neural and medical aspects of biological rhythmicity. Physiology professor Nathaniel Kleitman
Nathaniel Kleitman
Nathaniel Kleitman was Professor Emeritus in Physiology at the University of Chicago. Author of the seminal 1939 book Sleep and Wakefulness, he is recognized as the father of American sleep research...
'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
William C. Dement
William Charles Dement is a pioneering US sleep researcher, and founder of the Sleep Research Center, the world's first sleep laboratory, at Stanford University. He is a leading authority on sleep, sleep deprivation, and the diagnosis and treatment of sleep disorders such as sleep apnea and...
and Eugene Aserinsky
Eugene Aserinsky
Eugene Aserinsky , a pioneer in sleep research, was a graduate student at University of Chicago in 1953 when he discovered REM sleep. He made the discovery after hours spent studying the eyelids of sleeping subjects...
, 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.
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 Scale of Morningness (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
Shift work
Shift work is an employment practice designed to make use of the 24 hours of the clock. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts....
scheduling, travel fatigue and jet lag
Jet lag
Jet lag, medically referred to as desynchronosis, is a physiological condition which results from alterations to the body's circadian rhythms; it is classified as one of the circadian rhythm sleep disorders...
, athletic performance or best timing of medical procedures.
Characteristics
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 chronobiologyChronobiology
Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...
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, p. 109).
- Clodoré et al., France, 1986, found differences in alertness between morning and evening types after a two hour sleep reduction.
- Gibertini et al., US, 1999, assessed blood levels of the hormone melatoninMelatoninMelatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...
, 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., US, 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., US, 2000, found that, in young adults, the daily body temperature minimum occurred at about 4 a.m. for morning types but at about 6 a.m. 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 cortisolCortisolCortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
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."