Chronotypes: Morning, Evening, and Intermediate Sleep Timing Preferences
Chronotypes reflect genetically determined circadian phase; evening types show peak cognitive performance 2–4h later than morning types; PER3 length polymorphism affects chronotype and sleep architecture.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| MEQ score range | 16–86 | points | Morningness-Eveningness Questionnaire; <41 = evening type; >59 = morning type |
| Evening vs morning peak performance | 2–4 | hours later | Evening types' peak cognitive performance delayed by 2–4h vs morning types |
| Population distribution | ~25% morning, ~25% evening, ~50% intermediate | population | Roenneberg et al. 2007; social jetlag affects most of the 50% intermediate |
| Chronotype age shift | ~2h | earlier with age | Eveningness peaks in young adults (~20); shifts earlier throughout adulthood |
| PER3 4/4 genotype | Morning type | phenotype | PER3 5/5 genotype = evening type with worse sleep deprivation response |
| Social jetlag in evening types | 1–3 | hours daily | Mismatch between biological and social clock; associated with metabolic risk |
Definition and History
Chronotype refers to an individual’s preferred timing for sleep, wake, and peak performance — the subjective morning/evening tendency that reflects the phase of the underlying circadian clock. The concept was formalized by Horne and Östberg (1976) with their Morningness-Eveningness Questionnaire (MEQ), a 19-item self-assessment tool yielding scores from 16 (extreme evening type) to 86 (extreme morning type).
Modern chronobiology distinguishes chronotype from sleep duration preference — they are related but separable traits. An extreme evening type can still be a long sleeper or short sleeper; they simply prefer to sleep and wake later.
Genetic Basis
Multiple clock gene variants influence chronotype:
- PER3: A variable-number tandem repeat (VNTR) polymorphism with 4- or 5-repeat alleles. PER3 5/5 homozygotes (evening type) show greater sleep deprivation sensitivity — Viola et al. (2007) demonstrated more slow-wave activity in recovery sleep and worse waking performance after deprivation in this genotype
- CLOCK: rs1801260 variant associated with eveningness and delayed sleep phase
- CRY1: rare loss-of-function variants cause delayed sleep phase disorder (DSPD)
- Adenosine deaminase (ADA): alleles affect sleep homeostasis and interact with chronotype
Genome-wide association studies (GWAS) have identified >340 loci associated with chronotype (Jones et al., 2019), confirming its highly polygenic nature with estimated heritability of 40–60%.
Age and Sex Effects
Chronotype shows a characteristic developmental trajectory:
- Childhood: morning-preferring
- Adolescence: shift toward eveningness (peaks ~age 20 in men, ~age 19.5 in women)
- Adulthood: gradual shift toward morningness throughout life
- Older age: strong morning preference, with earlier wake times and earlier sleep
Duffy et al. (2011) demonstrated that women have slightly shorter intrinsic circadian periods than men (~24.09h vs ~24.19h), explaining why women tend to be slightly more morning-type on average.
Social Jetlag
Roenneberg’s concept of “social jetlag” describes the mismatch between biological clock and social schedule. For evening chronotypes required to start work at 8am, the biological clock is still in its early morning phase — equivalent to traveling westward 1–3 time zones every workday. This chronic misalignment accumulates as metabolic, cardiovascular, and cognitive consequences, particularly when sustained over years.
Estimated 40–60% of the population experiences some degree of social jetlag, with evening types disproportionately affected.
Related Pages
Sources
- Horne JA & Östberg O — A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. Int J Chronobiol (1976)
- Roenneberg T et al. — Epidemiology of the human circadian clock. Sleep Med Rev (2007)
- Viola AU et al. — PER3 polymorphism predicts sleep structure and waking performance. Curr Biol (2007)
- Duffy JF et al. — Sex difference in the near-24-hour intrinsic period of the human circadian timing system. Proc Biol Sci (2011)
Frequently Asked Questions
Is being a night owl (evening chronotype) genetic?
Yes, chronotype has substantial genetic basis — twin studies estimate heritability of ~50%. PER3, CLOCK, CRYPTOCHROME, and other clock gene variants influence chronotype. However, environment (light exposure, social schedule) modulates expression. Age is also a major factor: people are most evening-type in adolescence (~age 20) and shift progressively earlier through adulthood.
What is social jetlag?
Social jetlag is the chronic misalignment between the biological circadian clock and socially imposed schedules (work, school). Evening chronotypes who must wake for 8am work experience the equivalent of crossing 1–3 time zones every weekday. Roenneberg et al. found that each hour of social jetlag is associated with a 33% increased odds of being overweight.