PER 3 is a little known gene that you might not have heard of but it has an outsized effect on your natural proclivities when you go to bed (An et al, 2014). In other words, are you a morning type going to bed early and rising early (morning larks in whom the PER3 allele is longer) or an evening type going to bed late with late wake times (evening owls in whom the PER3 allele is shorter) or somewhere in between (intermediateness). This is known as your chronotype or your internal circadian clock (also colloquially known as the biological clock).
Surely, genetics is but one such factor that determines your eventual sleep-wake timings, but it does program you to be one type or the other. Evolutionary survival instincts also played a role in development of the chronotypes since night time was a vulnerable time for our ancestors, they had to keep watch throughout the night for predators or other kinds of dangers. The sentinel hypothesis proposes that group-living animals share the task of vigilance during sleep, with some individuals sleeping while others are awake (Samson et al, 2017).
Additionally, environmental factors, habits, lifestyles ,gender and age do swing the sleep pendulum. Chronotype becomes later in both sexes throughout adolescence, reaching a peak in ‘lateness’ at ~18 years for women and ~19 years for men. Men delay faster (going later to bed) between the ages of 15 and 20 and advance more slowly between 20 and 40, resulting in a later chronotype on average than women during this period. This pattern is reversed beyond 40 years of age, when men show earlier chronotypes than women (Fischer et al, 2017).
Dr. Michael J. Breus, a clinical psychologist and world renowned sleep expert disagrees with the chronotype triad and has come up with 4 class distinctions between chronotypes based on the chronotype quiz which addresses personality types, activity preferences and behavioral traits. He categorizes them as Lions, Bears, Wolves and Dolphins (Psychology Today, 2021).
Source: Calm.com
Interested in knowing what the scientifically validated scales tell you about chronotype? You can take a self assessment on the Morningness-Eveningness Questionnaire (MEQ) here or download a pdf offline here. It is important to know your chronotype not least due to the oversized effect the types have on your physical and mental health. Previous studies have found lower sleep quality ( Vitale et al, 2015), higher BMI (Culnan et al, 2013) and lower glycemic control in type 2 diabetes (Reutrakul et al, 2013) in evening types.
We all know what jet lag is. But have you heard of the Social Jet Lag (SJL) phenomenon? SJL is defined as the difference of hours between the midpoint of sleep on weekdays and weekends or in other words how late are you to bed on weekends with a hangover effect on mondays. Once again eveningness chronotypes have been implicated in higher SJL (Arora et al, 2015). in a series of studies SJL was associated with obesity, diabetes, depression and reduced academic performance, adverse endocrine, behavioral and cardiovascular health (Ronneberg et al, 2012; Haraszti et al, 2014; Koopman et al, 2017; Rutters et al, 2014; Wong et al, 2014; Zerbini et al, 2017).
Chronotypes and academic performance has received a lot of attention and later test timings have been proposed for Scholastic Achievement Test (Callan, 1995) to address the chronotype effect in students who are predisposed to eveningness. Additionally, time of day dependency has been found for cognitive abilities for different subjects (Wile et al, 2011) i.e. different subjects require different levels of thinking, reasoning etc and this varies by chronotypes and hence optimum teaching and testing schedules needs to be researched and even delayed school opening timings (Zerbini et al, 2017).
Not surprisingly, creativity also waxes and wanes during the day based on your chronotype. What matters is the alignment of the time of day and the chronotype in what Kuehnel, Bladow and Kiefer (2022) term as the synchrony effect. In eveningness chronotypes, the synchrony effect also gave rise to a positive mood and that led to creativity.
We know that physical exercises lift our mood but a (2019) study found that the effect depends on the chronotype for CrossFit training, which is a high intensity exercise with a variable rhythm. Morningness correlated with the mood before the exercise in the morning but not in the evening, which means that exercising in the morning has a positive effect on mood than in the evenings and this effect is true for even evening types, who came in with a much worse mood and left with an elevated positive mood. While the study was performed for CrossFit exercises, I suspect that effect would be similar for more moderate rhythmic exercises as well.
So, while there is an outsized effect of chronotypes on physical, mental, academic, creativity to name a few areas, it’s crucial that we
- Know which chronotype we are (see the MEQ link above)
- Understand that evening types has been correlated with more adverse effects than the morning types or intermediate types
- Discuss it with your sleep specialist and understand the steps (if any) that needs to be taken for your individual situation
- Change habits (turning morning or intermediate type) from evening type
So, what is your sleep animal?
References:
Kühnel, J., Bledow, R., & Kiefer, M. (2022). There is a time to be creative: The alignment between chronotype and time of day. Academy of management Journal, 65(1), 218-247.
Zerbini, G., & Merrow, M. (2017). Time to learn: How chronotype impacts education. PsyCh journal, 6(4), 263-276.
Wile, A. J., & Shouppe, G. A. (2011). Does time-of-day of instruction impact class achievement? Perspectives in Learning, 12, 21–25.
Callan, R. J. (1995). Early morning challenge: The potential effects of chronobiology on taking the scholastic aptitude test. Clearing House, 68, 174–176. https://doi.org/10.1080/000986 55.1995.9957224
Wong, P. M., Hasler, B. P., Kamarck, T. W., Muldoon, M. F. & Manuck, S. B. Social Jetlag, Chronotype, and Cardiometabolic Risk. J Clin Endocrinol Metab 100, 4612–4620, https://doi.org/10.1210/jc.2015-2923 (2015).
Rutters, F. et al. Is social jetlag associated with an adverse endocrine, behavioral, and cardiovascular risk profile? J Biol Rhythms 29, 377–383, https://doi.org/10.1177/0748730414550199 (2014).
Koopman, A. D. M. et al. The Association between Social Jetlag, the Metabolic Syndrome, and Type 2 Diabetes Mellitus in the General Population: The New Hoorn Study. J Biol Rhythms, 748730417713572, https://doi.org/10.1177/0748730417713572 (2017).
Haraszti, R. A., Ella, K., Gyongyosi, N., Roenneberg, T. & Kaldi, K. Social jetlag negatively correlates with academic performance in undergraduates. Chronobiol Int 31, 603–612, https://doi.org/10.3109/07420528.2013.879164 (2014).
Roenneberg, T., Allebrandt, K. V., Merrow, M. & Vetter, C. Social jetlag and obesity. Curr Biol 22, 939–943, https://doi.org/10.1016/j.cub.2012.03.038 (2012).
Arora, T. & Taheri, S. Associations among late chronotype, body mass index and dietary behaviors in young adolescents. Int J Obes (Lond) 39, 39–44, https://doi.org/10.1038/ijo.2014.157 (2015).
Reutrakul, S. et al. Chronotype is independently associated with glycemic control in type 2 diabetes. Diabetes Care 36, 2523–2529, https://doi.org/10.2337/dc12-2697 (2013).
Samson DR, Crittenden AN, Mabulla IA, Mabulla AZP, Nunn CL. Chronotype variation drives night-time sentinel-like behaviour in hunter-gatherers. Proc Biol Sci. 2017 Jul 12;284(1858):20170967. doi: 10.1098/rspb.2017.0967. PMID: 28701566; PMCID: PMC5524507.
Vitale, J. A. et al. Chronotype influences activity circadian rhythm and sleep: differences in sleep quality between weekdays and weekend. Chronobiol Int 32, 405–415, https://doi.org/10.3109/07420528.2014.986273 (2015).
An H, Zhu Z, Zhou C, Geng P, Xu H, Wang H, Chen R, Qu X, Qian H, Gao Y, Zhao X, Qian Y. Chronotype and a PERIOD3 variable number tandem repeat polymorphism in Han Chinese pilots. Int J Clin Exp Med. 2014 Oct 15;7(10):3770-6. PMID: 25419431; PMCID: PMC4238505.
Fischer D, Lombardi DA, Marucci-Wellman H, Roenneberg T. Chronotypes in the US – Influence of age and sex. PLoS One. 2017 Jun 21;12(6):e0178782. doi: 10.1371/journal.pone.0178782. PMID: 28636610; PMCID: PMC5479630.
https://www.psychologytoday.com/us/blog/sleep-newzzz/202104/the-four-chronotypes-which-one-are-you
Culnan, E., Kloss, J. D. & Grandner, M. A prospective study of weight gain associated with chronotype among college freshmen. Chronobiol Int 30, 682–690, https://doi.org/10.3109/07420528.2013.782311 (2013).