As diurnal beings, we are biologically programmed to be awake during the day period and asleep throughout the night. This is largely controlled by our circadian rhythm generated by the suprachiasmatic nucleus, our internal biological clock. Nevertheless, as we all know all too well, there is large individual variability in when we prefer to go to sleep and wake up. Some of us can easily be in bed and asleep before 10 o’clock while others struggle to fall asleep, sometimes even until the early morning hours, and this regardless of how tired or sleep deprived you may be.
Our chronotype refers to the preferred timing throughout the day-night period for when we sleep, as well as for activities and performance during wakefulness. Specifically, chronotype influences more than just our preferred sleep and wake schedule, but also corresponds to our diurnal performance profiles, including peak periods cognitive and physical performance throughout the day.
Chronotypes are most popularly defined as two categories;
- morning types (larks), who prefer an earlier schedule and perform better in the morning time;
- evening types (owls), who prefer an later schedule and perform more optimally in the later part of the day.
I for one find myself to be more of a morning type, finding it easy to be productive in the early hours of the morning, sometimes even before having enjoyed a sip of coffee.
However, instead of dichotomic categories where you are either one or the other, chronotype should instead be referred to as a spectrum, with morning-type and evening-type at each end. This would further show the different intensities for each of the two extremes. As such, chronotype is most traditionally measured using the Morningness-Eveningness Questionnaire (MEQ) developed by Horne and Östberg in 1976. The questionnaire holds 19 questions and provides a score between 16 and 86, which is then separated into 5 categories: definite morning, moderate morning, intermediate (neither), moderate evening, and definite evening.
An individual’s chronotype is, in part, genetically based/determined/dependent and is strongly linked to our internal circadian rhythm. However, a person’s chronotype will shift throughout one’s life time.
One very common shift is that of teenagers and young adults. During these years, individuals tend to shift more to the evening-type (night owl) side of the spectrum, where there is a biological preference for going to bed and waking up at a later time. This shift may be a result of hormonal changes associated with puberty, and is further endorsed by their social environment promoting the evening-type lifestyle. For parents, this means that their teenager’s habits of not waking up before the late morning or early afternoon is not necessarily a sign of laziness, but rather a biological shift in their chronotype to a later time.
This common shift to an evening chronotype tends to decrease come adulthood, while the morning chronotype is more common in the senior and elderly population, who have a biological preference for an earlier bed- and wake-time.
What is interesting, however, is that contrary to the popular belief that you are either a morning- or an evening-type, the shape of distribution is much like that of a normal, bell-shaped curve where the majority of individuals fall within the center area and only a few are found in the extremes of the spectrum. A such, about 40% fall within the morning-type, 30% within the evening-type, while the last 30% are in the ‘neither’ category.
Extreme morning-types often find themselves awake in the early hours of the morning, and are unable to prolong sleep come evening time regardless of social demands (ex. attending a party). On the other hand, extreme evening-types find great difficulty in getting up in the morning, sometimes being unable to do so or falling back asleep after an initial wake-up, but would often find themselves wide awake throughout the night. This clashes with the general social demands of needing to attend school or work in the morning and day-time period.
While the extreme chronotypes may be more biologically driven, often times hindering or interfering with social demands, for individuals who find themselves more along the spectrum’s mid-line, particularly those in the ‘neither’ section, their preferences may be more dependent on their lifestyles, habits and social demands (work, school, family, etc.).
In these cases, it is important to adopt daily behaviours and habits, including utilizing good sleep hygiene techniques (see The Sleepyhead’s Sleep Hacks) to maintain a good balance between a person’s internal chronotype and external lifestyle and social demands. Optimizing this relationship will not only improve sleep quality and duration, but will also increase performance and overall health and well-being.
- Horne, J.A. & Östberg, O. (1976). A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. International Journal of Chronobiology, 4, 97-110.
- Duffy, J. F., Rimmer, D. W., & Czeisler, C. A. (2001). Association of intrinsic circadian period with morningness–eveningness, usual wake time, and circadian phase. Behavioral Neuroscience, 115(4), 895-9.
- Mongrain, V., Lavoie, S., Selmaoui, B., et al. (2004). Phase relationships between sleep-wake cycle and underlying circadian rhythms in morningness-eveningness. Journal of Biological Rhythms, 19(3), 248-57.
- Facer-Childs, E. R., Boiling, S., & Balanos, G. M. (2018). The effects of time of day and chronotype on cognitive and physical performance in healthy volunteers. Sports medicine-open, 4(1), 1-12.
- Carskadon, M. A., Vieira, C., & Acebo, C. (1993). Association between puberty and delayed phase preference. Sleep, 16(3), 258-262.
- Walker, M. (2017). Why we sleep: Unlocking the power of sleep and dreams. Simon and Schuster.