Chronotype

Abstract

Chronotype is a person's characteristic preference for the time of day at which activity and sleep fall, ranging along a continuum from morning types to evening types. MeSH classifies chronotype under personality. It is assessed either with morningness-eveningness questionnaires or as the clock time of mid-sleep on free days, and it shifts with age and differs between the sexes. Genome-wide studies have located hundreds of associated loci, whose combined effect on sleep timing is modest. Chronotype relates to personality traits, to cognitive performance that depends on the hour of testing, to social jetlag, the mismatch between social and biological timing, and, weakly, to depressive symptoms.

Keywords: chronotype, morningness-eveningness, social jetlag, circadian rhythm, sleep timing

Chronotype research belongs to the field of circadian typology, whose reach, as one review sets out, runs from the sleep-wake cycle and rhythms of body temperature, cortisol and melatonin, across adjustment to shiftwork and jet lag, to cognitive abilities, personality traits and psychiatric disorders (Adan et al., 2012). The same comprehensive review noted methodological limitations across that literature and set out directions for further work (Adan et al., 2012).

The topic matters to cognitive psychology because timing preference is measurable at scale and varies systematically between people. Survey data from more than 55,000 respondents to the Munich ChronoType Questionnaire show chronotype to depend on age and sex, and they show sleep timing and sleep duration to be, in general, independent of one another (Roenneberg et al., 2007).

What Chronotype Is

MeSH defines Chronotype as the natural inclination or preference of time of day in which an individual or an organism has the most activity, particularly as it relates to sleeping pattern and circadian sleep-wake preferences. It lists Morningness Eveningness Preferences as an entry term and files the descriptor under personality.

The entry term names the same dimension from the questionnaire side: a morningness-eveningness preference is a self-described tendency to be active early or late. At one end stand morning types, colloquially larks; at the other stand evening types, or owls. Sleep timing emerged as multifactorial, with influences including genetic disposition and light exposure, in a pilot study that analysed 500 returns of a new chronotype questionnaire; more light exposure advanced sleep, though both light exposure and chronotype were self-assessed there (Roenneberg et al., 2003).

Earlier work had already singled out this axis. Of the individual differences in the human circadian system that Kerkhof weighed, introversion-extraversion among them, morningness-eveningness yielded the most dependable contrasts between people (Kerkhof, 1985). The field now files these differences under circadian typology, a construct whose reach spans biology, psychology and health (Adan et al., 2012).

Measuring Chronotype

Horne and Östberg introduced a self-assessment instrument for measuring morningness-eveningness (Horne & Östberg, 1976). It became known as the Horne-Östberg Morningness-Eveningness Questionnaire, or MEQ (Zavada et al., 2005). Preference scales did not escape criticism. When Smith and colleagues examined three morningness scales in 501 undergraduates, they judged every one psychometrically deficient and put forward a 13-item composite scale in their place, a proposal resting on self-report data from a student sample (Smith et al., 1989).

A different strategy asks for clock times. The Munich ChronoType Questionnaire (MCTQ) collects sleep timing separately for work days and for free days (Roenneberg et al., 2003). The split is not cosmetic: work-day sleep duration varies with chronotype, and that relation emerges only when the two kinds of day are analysed apart (Roenneberg et al., 2007).

The two families of measure largely converge. Among 5,055 Dutch Internet responders, 2,481 completed both instruments; in that subgroup the Horne-Östberg score tracked MCTQ mid-sleep on free days closely (r = - 0.73) and mid-sleep on workdays less closely (r = - 0.61), and the MCTQ supplied more detailed sleep-wake information than the preference score alone (Zavada et al., 2005).

Table 1 sets out four of the measures used in this literature.

Chronotype Across the Lifespan

Chronotype is not a constant. Roenneberg and colleagues put chronotype forward as a possible marker for the end of adolescence (Roenneberg et al., 2004), and survey data from the Munich ChronoType Questionnaire show that it varies with both age and sex (Roenneberg et al., 2007). The point was not settled earlier: in 1985 a review found the evidence on age and sex differences insufficient (Kerkhof, 1985).

A large-scale US population picture comes from the American Time Use Survey. Pooling 12 years of 24-hour diary recalls from 53,689 US respondents, Fischer and colleagues placed peak lateness at roughly 19 years of age, after which mid-sleep shifted steadily earlier (Fischer et al., 2017). Two limits shape how far the curve can be read. Each respondent was observed once, so the pattern contrasts age groups rather than following people as they age, and weekend sleep had to stand in for work-free days, with alarm-clock use unknown (Fischer et al., 2017).

The Biology of Chronotype

Timing preference has a physiological counterpart. In a month-long inpatient circadian study, intrinsic circadian period was associated with morningness-eveningness, with circadian phase and with usual wake time, although phase was assessed in only a subset of participants (Duffy et al., 2001). A review names three routes by which chronotype may be assessed or may differ physiologically: the kinetics of homeostatic sleep pressure, the intrinsic circadian period and the phase angle of entrainment (Taillard et al., 2021).

Candidate-gene work then pointed to specific clock genes. A length polymorphism in Per3 was linked both to extreme diurnal preference, in participants classified with the Horne-Ostberg questionnaire, and to delayed sleep phase syndrome in patients; the authors presented it as no more than a potential genetic marker (Archer et al., 2003). In familial delayed sleep phase disorder, marked by late and/or fragmented sleep, a gain-of-function variant of CRY1 lengthened the circadian period; reverse phenotyping in unrelated families corroborated the association without proving it (Patke et al., 2017).

Genome-wide association studies widened the search. Twelve chronotype loci not reported before emerged when Lane and colleagues scanned the genomes of 100,420 UK Biobank participants who had rated their own chronotype; Mendelian randomization gave suggestive evidence linking an evening chronotype with higher educational attainment, and genetic correlations pointed to pathways shared with schizophrenia and, less certainly, with BMI (Lane et al., 2016). A later analysis of 697,828 UK Biobank and 23andMe participants raised the count of morningness loci from 24 to 351 (Jones et al., 2019). Among 85,760 individuals with activity-monitor data, the 5% carrying the most morningness variants slept about 25 min earlier than the 5% with the fewest, and Mendelian randomisation tied morningness to better mental health while showing no effect on either BMI or Type 2 diabetes (Jones et al., 2019). Taking stock of three landmark studies, a review found 9 genes common to 2 of the 3, stressed that the samples were of European ancestry only, and left the contribution of rare variants open (Kalmbach et al., 2017).

Chronotype and Personality

Personality traits are among the domains that reviews of circadian typology cover (Adan et al., 2012). The 1985 review had reported differences along introversion-extraversion and argued that they were the result of exogenous influences (Kerkhof, 1985).

Within the five-factor model, conscientiousness carries most of the signal. Among 503 participants (280 women and 223 men) who completed the Morningness-Eveningness Questionnaire and the Big Five Observer, conscientiousness separated the three circadian types better than any other domain; morning types scored higher on it than evening types, and evening types were more neurotic than morning types, with all measures self-reported (Tonetti et al., 2009). Proactivity follows a similar pattern. Morning types exceeded evening types on proactivity, whereas neither sleep length nor weekend oversleep showed any relation to it (Randler, 2009).

Chronotype and Cognition

Cognitive performance varies across the day, and chronotype changes how it varies. Surveying research on healthy subjects, Schmidt and colleagues described time-of-day effects on attention, executive functions and memory, and argued that performance depends on the match between chronotype and testing time, the synchronicity or synchrony effect; they also noted how seldom studies took time of day into account (Schmidt et al., 2007). A later review puts the synchrony effect's standing more cautiously: the effect often appears when people sleep at their preferred times, but not always (Taillard et al., 2021).

The synchrony idea has a well-known test in ageing research. After a norming study of optimal performance periods in younger and older adults, May, Hasher and Stoltzfus measured recognition memory in the morning and in the late afternoon; the age difference was present in the late afternoon and absent in the morning (May et al., 1993). The finding concerns recognition memory alone and only those two testing times (May et al., 1993).

More recent laboratory work compared early and late chronotypes among 56 healthy volunteers, classified with the Munich ChronoType Questionnaire, actigraphy and circadian phase markers, on a battery spanning daytime sleepiness, psychomotor vigilance, executive function and grip strength; late chronotypes were impaired when tested in the morning (Facer-Childs et al., 2018). Beyond the laboratory, a meta-analytic investigation examined how chronotype relates to cognitive abilities and to academic achievement (Preckel et al., 2011). A later review found evening types cognitively more vulnerable at suboptimal times, called the cognitive impact of sleep and circadian disruption still to be clarified, and suggested that circadian disruption, but not chronotype, may impair inhibition (Taillard et al., 2021).

Social Jetlag and Health

Social jetlag is the gap between when a person sleeps on work days and on free days, and so a misalignment between social and biological time (Wittmann et al., 2006). In a questionnaire survey of 501 volunteers, the authors judged the associations of chronotype with psychological wellbeing and stimulant consumption to be most probably a consequence of social jetlag rather than of chronotype itself; the data were correlational, the relations were strongest below age 25, and a causal role was judged only probable (Wittmann et al., 2006).

Mood has drawn particular attention. In a rural population of 4051 participants, higher Beck Depression Inventory scores went with later chronotype and with more social jetlag, most strongly in the 31-40 age group; the authors treated social jetlag as a risk factor rather than a demonstrated cause and called for longitudinal studies (Levandovski et al., 2011). A meta-analysis of 36 studies (n = 15734, 58 effect sizes) found eveningness associated with depressive symptoms at a small magnitude (z = -.20, 95% CI: -.18 to -.23), with larger effects for the Composite Scale of Morningness than for the Morningness-Eveningness Questionnaire, no evidence of publication bias, and a causal direction that remains unclear (Au & Reece, 2017).

Physical health findings are similarly modest. Across 433 268 UK Biobank adults aged 38-73, followed for 6.5 years, evening type was associated with a small increase in mortality risk; the association with cardiovascular mortality did not reach significance (p = 0.06), and chronotype rested on a single self-reported question (Knutson & von Schantz, 2018). Reviewing the psychiatric evidence, Taillard and colleagues noted that evening types are overrepresented among people with mood disorders and with ADHD, while judging the link between social jetlag and psychiatric disorders less obvious (Taillard et al., 2021).

Shifting a Late Chronotype

Late timing can be moved. In a randomized controlled trial with night owls, sleep and circadian timing, indexed by actigraphy, dim light melatonin onset and the cortisol awakening response, advanced by about 2 h without an adverse effect on sleep duration, and participants reported lower depression and stress; the trial also assessed reaction time and grip strength (Facer-Childs et al., 2019). The depression and stress outcomes were self-reported (Facer-Childs et al., 2019).

Worked Example

The MCTQ approach reduces a sleep schedule to its midpoint on each kind of day: the mismatch between workday and free-day sleep timing is what Wittmann and colleagues called social jetlag (Wittmann et al., 2006), while the free-day midpoint is the questionnaire's index of chronotype (Zavada et al., 2005). The full MCTQ chronotype score goes one step further and adjusts free-day mid-sleep for the sleep lost over the workweek, a correction Fischer and colleagues could not apply because the US diaries recorded no prior sleep; the 06:00 in this example is likewise left uncorrected (Fischer et al., 2017). Its chronotype algorithm uses sleep timing from both work days and free days (Roenneberg et al., 2007), and late types run up a sleep debt during the working week that they repay on free days (Roenneberg et al., 2003). The following numbers are illustrative arithmetic only and come from no study.

Suppose a person sleeps from 23:30 to 06:30 on workdays. That is 7 h of sleep, and the midpoint falls 3.5 h after onset, at 03:00. On free days the same person sleeps from 01:30 to 10:30, which is 9 h, with the midpoint 4.5 h after onset, at 06:00. Mid-sleep on free days is therefore 06:00, and the difference between the free-day and workday midpoints, 06:00 minus 03:00, gives a social jetlag of 3 h. The longer free-day sleep (9 h against 7 h) is a separate quantity from the shift in timing. The MidSleepDemo performs the same arithmetic for any schedule entered into it.

Figure 1 draws the two schedules on one clock.

Figure 1

Workday and Free-Day Sleep in the Worked Example

Discussion

The measures of chronotype agree in direction but not in kind. A preference score and the clock time of free-day mid-sleep correlate strongly, yet the correlation is weaker when workday mid-sleep is used instead (Zavada et al., 2005). The difference matters whenever a study reports chronotype from a single self-reported question, as the UK Biobank mortality cohort did (Knutson & von Schantz, 2018).

Most of the health literature is correlational and its effects are small. The depression association showed no evidence of publication bias, but its magnitude is small and its direction undetermined (Au & Reece, 2017), and the mortality signal in the UK Biobank was slight (Knutson & von Schantz, 2018). Genetic findings temper any strongly deterministic reading: hundreds of loci together shift sleep timing by minutes rather than hours (Jones et al., 2019), and the evidence comes almost entirely from samples of European ancestry (Kalmbach et al., 2017). The review literature itself flags methodological limitations in the field (Adan et al., 2012).

Current Directions

Very large genetic samples now allow Mendelian randomization designs, which ask whether chronotype plays a causal part in outcomes such as education, BMI and mental health (Lane et al., 2016; Jones et al., 2019). Intervention research is testing whether advancing the timing of night owls improves mental health and performance (Facer-Childs et al., 2019). A third line examines what social jetlag and late timing do to cognitive abilities and to psychiatric disorders, a question reviewers regard as open (Taillard et al., 2021).

Common Misconceptions

A person's chronotype is fixed for life.

Population data show lateness peaking near 19 years and moving earlier afterwards, although that survey compared age groups cross-sectionally rather than following individuals (Fischer et al., 2017).

Being an evening type causes depression.

Eveningness is associated with depressive symptoms, but the effect is small and the causal direction is unclear (Au & Reece, 2017). Even the population study linking late chronotype and social jetlag to depression scores framed social jetlag as a risk factor, not a cause (Levandovski et al., 2011).

A single gene decides whether someone is a lark or an owl.

Genome-wide work has identified 351 loci associated with morningness (Jones et al., 2019), and 9 genes recurred in 2 of 3 landmark studies, which the reviewers described as a good deal of consistency (Kalmbach et al., 2017). Single-gene findings such as the CRY1 variant come from families with delayed sleep phase disorder, a clinical condition, and they do not show that the ordinary spread of chronotypes in the population rests on one gene.

Late types simply sleep too little.

Sleep timing and sleep duration are generally independent; a link between chronotype and duration appears for work-day sleep, and only when work days and free days are analysed separately (Roenneberg et al., 2007).

Glossary

Chronotype.

A person's characteristic preference for the time of day at which activity and sleep occur, ranging from morning types to evening types.

Circadian typology.

The umbrella term for individual differences in circadian timing, of which morningness-eveningness is the principal dimension.

Composite Scale of Morningness.

A self-report morningness questionnaire; in meta-analysis it produced larger associations with depressive symptoms than the Morningness-Eveningness Questionnaire.

Delayed sleep phase disorder.

A circadian sleep disorder characterised by persistently late, and sometimes fragmented, sleep; earlier literature calls it delayed sleep phase syndrome.

Evening type.

A person at the late end of the chronotype continuum, colloquially an owl.

Genome-wide association study.

A study that tests genetic variants across the whole genome for association with a trait, here self-reported or measured chronotype.

Intrinsic circadian period.

The length of the internal clock's cycle when it runs free of external time cues; it is associated with morningness-eveningness and wake time.

Mendelian randomisation.

An analysis that uses genetic variants as proxies for an exposure, such as chronotype, to probe whether it causally affects an outcome.

Mid-sleep on free days.

The clock time halfway between sleep onset and waking on days without work obligations; the basis of the chronotype measure derived from the Munich ChronoType Questionnaire.

Morning type.

A person at the early end of the chronotype continuum, colloquially a lark.

Morningness-Eveningness Questionnaire.

The self-assessment preference scale introduced by Horne and Östberg, abbreviated MEQ.

Munich ChronoType Questionnaire.

A questionnaire, abbreviated MCTQ, that records sleep times separately for work days and free days; the chronotype it yields is based on mid-sleep on free days.

Social jetlag.

The difference between sleep timing on work days and on free days, expressing a misalignment of social and biological time.

Synchrony effect.

The dependence of cognitive performance on the match between a person's chronotype and the time of testing; also called the synchronicity effect.

Key Researchers

Lynn Hasher

Psychologist at the University of Toronto and the Rotman Research Institute, Baycrest; with colleagues, tested how testing older and younger adults at their optimal time of day affects age differences in recognition memory. Wikipedia - Wikidata - Google Scholar - Faculty Page

James A. Horne

(1946–2023). Psychophysiologist at Loughborough University's Sleep Research Centre; with Olov Östberg, devised a self-assessment questionnaire of morningness–eveningness. Wikipedia - Wikidata - Faculty Page

Martha Merrow

(b. 1957). Chronobiologist at the Institute of Medical Psychology, Ludwig-Maximilians-Universität Munich; co-author of work on how human chronotypes are distributed, on social jetlag, and on chronotype as a possible marker for the end of adolescence. Wikipedia - Wikidata - Faculty Page

Christoph Randler

Biologist at the University of Tübingen; related morningness–eveningness to proactivity and co-authored a review of circadian typology. ORCID - Faculty Page

Till Roenneberg

(b. 1953). Chronobiologist at the Institute of Medical Psychology, Ludwig-Maximilians-Universität Munich; introduced a questionnaire that records sleep on work days and free days separately, and studied chronotype across age and sex and the mismatch between social and biological time termed social jetlag. ORCID - Wikipedia - Wikidata

Frequently Asked Questions

What is a chronotype?

A chronotype is an individual's typical preference for being active and asleep earlier or later in the day. Researchers study it under the heading of circadian typology, which bears on biology, psychology and health (Adan et al., 2012).

How is chronotype measured?

Researchers use either a preference questionnaire such as the Morningness-Eveningness Questionnaire or the Munich ChronoType Questionnaire, which yields mid-sleep on free days. The two correlate strongly, at r = - 0.73 for free days, and less so for workdays (Zavada et al., 2005).

Does chronotype change with age?

Yes. In a large US diary survey, lateness peaked at about 19 years and became earlier with age after that, though the data were cross-sectional (Fischer et al., 2017).

Is chronotype genetic?

Partly. A genome-wide study of 697,828 participants identified 351 loci associated with morningness, yet the 5% of individuals with the most morningness variants had sleep timing only about 25 minutes earlier than the 5% with the fewest (Jones et al., 2019).

What is social jetlag?

Social jetlag is the gap between sleep timing on work days and on free days, reflecting a misalignment of social and biological time. In a survey of 501 volunteers, links of chronotype with wellbeing and stimulant use were judged most probably a consequence of social jetlag rather than of chronotype itself (Wittmann et al., 2006).

Are evening types more prone to depression?

Eveningness is associated with more depressive symptoms, but a meta-analysis of 36 studies found the effect small and could not establish which way causation runs (Au & Reece, 2017).

Does time of day affect memory and attention?

Attention, executive functions and memory all vary with time of day, and Schmidt and colleagues argued that performance depends on how well testing time matches a person's chronotype (Schmidt et al., 2007).

Can a late chronotype be shifted earlier?

A randomized controlled trial advanced the sleep and circadian timing of night owls by about 2 h, and participants reported less depression and stress, without harm to sleep duration (Facer-Childs et al., 2019).

References