Are You An Early Bird or A Night Owl?

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Are you an Early Bird, a Night Owl, or Something In-between? Two New Chronotypes Have Been Discovered

Humans like most other animals are diurnal which means they are neurally programmed to be active during the day and then sleep at night. The timing, personal desire, environment and other constraining factors shape wake-sleep behavior. This is mainly due to industrialization and technology which makes artificial light available at any time, visual devices like television, computers, and smartphone, idiosyncratic diet, use of stimulants, and living irregular hours as necessary. Chronotype is a technical term for a person’s individual circadian rhythms which include sleep cycles, body temperature, cortisol responses, cognitive functions, and eating patterns. It is shaped by internal external factors and this pattern affects health and well-being over time. A new model of chronotype asserts it is also influenced by social and environmental factors as well (Chauan et al., 2023).

Some 18^th century scientists thought that the operations of the human body were a homeodynamic balance of many, many opposing forces (Reill, 2005). While this is incorrect it also vaguely rings true in an odd. Instead of forces, our somatopsychic functions are governed by many, many inter-locking, circular cycles, the most famous of which must the circadian sleep-wake rhythm and closely followed by the menstrual cycle.

The circadian system of warm-blooded, mammals is comprised of multiple rhythmic cells in the organs and tissues. Body time is orchestrated at the cellular level and moving up in a hierarchical manner through the 24-hour day. At the top of the hierarchy of rhythmic control is the suprachiasmatic nucleus (SCN) at the end of the optic nerve as it enters the brain. The SCN coordinates the clocks inside of the organs and other tissues via electrical, hormonal, and metabolic pathways. Thus, the circadian cycle springs from the molecular level of the human body. The interactive relationship between the tissue clocks of the central and peripheral nervous systems is not fully understood and remains a major question. The body’s clockwork system can be destabilized and fall out of kilter with one another. This results in health problems such as obesity and neuropsychiatric disorders (Albrecht, 2012).

The regulation cycle of the human circadian system begins with the amount of light hitting the retina of the eye. This then signals the SCN which, in turn, alerts the hypothalamus to have the pineal gland increase or decrease its release of melatonin. “Clock genes” govern cycles via intra-cellular feedback loops. Besides the pineal gland, immune cells also produce melatonin. These are controlled by their own clock genes and the SCN itself and so body sleep-wake time is strongly integrated with immune system functions (Berger, 2004).

The circadian system orchestrates the many operations of human physiology. The circadian system is a complex feedback network that involves interactions between the central and peripheral nervous systems very much like the metabolic system. New research evidence indicates that circadian regulation is directly tied to metabolic homeostasis and that dysregulation of circadian rhythms contributes to disease. By the same token, metabolic signals feed back into the circadian system and help its operations (Green, Takahashi, & Bass, 2008). Given all of this, it is now known that patterns of waking and sleeping as well as successfully performing difficult intellectual and physical tasks at different times of the day are rooted in biology (DeYoung et al., 2007).

Morning vs. Evening (M/E) Types

Everyday people have long believed in the “morning person” and “night person” dichotomy and as we see a great deal of scientific evidence from the field of chronobiology has affirmed it. Preference for sleep and wake times has become the first individual difference in human daily rhythms documented by using both subjective and objective measurements as early as in the end of 19th century by German psychiatrist, Emil Kraepelin (1856–1926). Kraepelin discovered morning and evening alertness orientation and intermediate types based on a person’s physical capacity, cognitive ability and alertness/sleepiness during the day as well as his or her sleeping habits (Becker, Steinberg, & Kluge, 2016). The exact cause of the M/E predisposition remains unknown but there is some evidence that it may partly be a function of the season of birth. Researchers have found more morning types of people born in autumn and winter than in spring and summer. They found the opposite pattern for evening types (Natale & Adan, 1999).

Physiological studies of M/E types show that morning persons have the highest cortisol level upon awakening as well as a greater overall cortisol output in general (Petrowski, Schmalbach, & Stalder, 2020). Thus, morning people have higher energy levels in the morning than others (Tsaousis, 2010).

Several personality traits are slightly to moderately related to M/E. Morning and evening types have related personality traits, cognitive styles, and are affected by social factors which help entrain their circadian rhythms (Matthews, 1998). In general, the morning type is slightly more introverted, high on conscientiousness, agreeableness, self-esteem, and internal locus of control. They are more likely to have stable personalities (DeYoung et al., 2007; Jackson & Gerard, 1996; Tsaousis, 2010).

Evening types are slightly more extroverted (Jackson & Gerard, 1996). They tend to have more radical political stances and are mor apt to have poor self-image. The female evening personality is associated with extraversion and independence. Evening people are more likely to have a mild psychopathology (Matthews, 1988). Eveningness is also associated with youth and depression. In fact, some researchers believe that the transition from the staying up late teenager to a young adult on a conventional sleep cycle is the major transition point between adolescence and adulthood (Roenneberg et al., 2004)

Two New Types: Nappers and Opposing Afternoon Types

Now new evidence has come forth showing that this duality is now a quadrinity. There are some types of people who are neither morning nor intermediate nor evening types. They are just very in-between. Napper types are sleepier in the afternoon than in the morning or evening. The opposing afternoon types are sleepy in both the morning and in the evening (Putilov et al., 2019).

Closing Thoughts

I definitely know I’m a morning person for two reasons. First, I usually awake fully alert and in a good mood. Second, I worked night shift at a residential adolescent psychiatric center for almost four years and basically felt as if I were in a perpetual state of jet lag. Now that’s learning the hard way. And now, as I enter old age, I find myself much sleepier in the afternoons and so must take a little catnap as needed. I guess I am now part morning-person and afternoon-napper. In any event, research into chronobiology is very illustrative of how the body’s cycles influence mood, personality, and behavior.

Paul Shane, Ph.D., LMT

References

Albrecht, U. (2012). Timing to perfection: The biology of central and peripheral circadian clocks. Neuron 74, p. 246-260.

Berger, J. (2004). Regulation of circadian rhythms. Journal of Applied Biomedicine 2, p. 131-140.

Chauhan, S., Norbury, R., Faßbender, K., Ettinger, U., & Kumari, V. (2023). Beyond sleep: A multidimensional model of chronotype. Neuroscience & Biobehavioral Reviews 148, 105114, https://doi.org/10.1016/j.neubiorev.2023.105114.

DeYoung, C., Hasher, L., Djikic, M., Criger, B., & Peterson, J. (2007). Morning people are stable people: Circadian rhythm and the higher-order factors of the Big Five. Personality and individual Differences 43, p. 267-276.

Green, C., Takahashi, J., & Bass, J. (2008). The meter of metabolism. Cell 134, p. 728-742.

Jackson, L. & Gerard, D. (1996). Diurnal types, the “Big Five” personality factors, and other personal characteristics. Journal of Social Behavior and Personality 11(2), p. 273-

Matthews, G. (1988). Morningness-eveningness as a dimension of personality: Trait, state, and psychophysiological correlates. European Journal of Personality 2, p. 277-293.

Natale, V. & Adan, A. (1999). Season of birth modulates morningness-eveningness preference in humans. Neuroscience Letters 274(2), p. 139-141.

Petrowski, K., Schmalbach, B., & Stalder, T. (2020). Morning and evening type: The cortisol awakening response in a sleep laboratory. Psychoneuroendocrinology 112, 104519, https://doi.org/10.1016/j.psyneuen.2019.104519.

Putilov, A., Marcoen, N., Neu, D., Pattyn, N., & Mairesse, O. (2019). There is more to chronotypes than evening and morning types: Results from a large-scale community survey provide evidence for high prevalence of two further types. Personality and Individual Differences 148, p. 77-84.

Reill, P. (2005). Vitalizing Nature in the Enlightenment. Berkeley, CA: University of California Press.

Roenneberg, T., Kuehnle, T., Pramstaller, P., Ricken, J., Havel, M., Guth, A., & Merrow, M. (2004). A marker for the end of adolescence. Current Biology 14, R1038-R. 1039.

Tsaousis, I. (2010). Circadian preferences and personality types: A meta-analysis. European Journal of Personality 24, p. 356-373.

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