The importance of chronotype to mental health

The article by Tsapakis et al. explores the role of circadian preference as predictor of emotional well-being. In their work Tsapakis and colleagues recruited a heterogeneous group of patients with mood disorders, psychotic disorders and other diagnoses and assessed the role of circadian preference in determining the level of emotional well-being. Notably, the “emotional-wellbeing” factor consisted of several psychopathological domains such as depression, anxiety and suicidality as well as quality of life (Tsapakis et al., 2024). While the design of the study does not allow for analysis of complex interactions between chronotype and particular symptoms or diagnoses, it helps deliver a clear message: that circadian preference is a significant aspect of mental health.

The work by Tsapakis and colleagues (Tsapakis et al., 2024) sparks interest as chronobiological factors and their associations with mental health don't seem to get the spotlight they deserve. Historically, the research into circadian typology has started in the 20th century (Adan et al., 2012; Di Milia et al., 2013). Chronotype defined as a unidimensional feature, constitutes an individuals preference for activity and sleep during particular times of the 24-h period (Francis and Porcu, 2023). The literature describes three chronotypes: morning (prefers to go to bed early, get up early; best physical and mental performance early in the day), evening (prefers to go to bed late, get up late; best physical and mental performance towards the end of the day) or neither (which some authors describe as intermediate) (Adan et al., 2012; Di Milia et al., 2013). Centrally the circadian rhythm is dictated by the suprachiasmatic nucleus, a central biological pacemaker, but diurnal oscillations in gene expression are present in multiple peripheral tissues (Francis and Porcu, 2023). While the majority of our society presents intermediate chronotypes, it has long been disputed that those with extreme evening preference are prone to adverse health outcomes (Hebl et al., 2022).

The data indicating the role of circadian rhythm disruption and higher eveningness as risk factors for affective disorders is robust, it was also noted, that evening preference is linked to resistance to antidepressant pharmacotherapy (Anmella et al., 2023; Krupa et al., 2023). More recent data shows that evening chronotype is also linked to schizophrenia, anxiety and substance abuse (Linke and Jankowski, 2021). Moreover, late-evening chronotypes are at higher risk of strictly “somatic” diseases such as metabolic syndrome, diabetes mellitus and obesity (Hebl et al., 2022).

One way to understand the role of eveningness as a predisposition for mental health issues is via the concept of social jet lag (SJL). While the understanding of diurnal misalignment seems largely related to shift-work research, it can be applied to non-working population with pronounced eveningness. SJL refers to the misalignment between the biological clock of people with i.e. evening preference and the social zeitgeber, which is commonly in keeping with morning preference (i.e. early morning start of school or workplace activities). Hence, in order to comply with the societal expectations, people with evening chronotype have to function outside their biologically dictated time zone that is: go to bed early, get up early in the morning, perform physically and intellectually in the early hours etc., but they clock-back to match their own preference when possible and commonly sleep-in on weekends and work-free days, only to later go back to the routine dictated by school/work hours when they have to. These constant oscillations between preferred “night owl” and mandatory “early bird” schedule translates to chronic misalignment with their natural preference, disruption of circadian rhythms and induces chronic stress. Indeed, data corroborates the association between the SJL and risk of anxiety symptoms, poor eating habits, higher body mass index, somatic morbidity and worse economic performance (Hebl et al., 2022).

In their study, Tsapakis and colleagues evaluated chronotypes with the Morningness–Eveningness Questionnaire (MEQ), which was among the first tools constructed to measure diurnal preference and remains among the most popular ones. It's worth noting that the majority of available chronobiological scales assess for subjective, trait-like, self-reported circadian preference (Putilov et al., 2021). Diurnal preferences are known to evolve throughout the lifespan and are dependent on current external environment, which varies depending or school/work schedule, light exposure, social cues, medical conditions and treatments among others. Therefore, in order to discern the interrelations between chronotype and health, functioning and quality of life outcomes, a combination of subjective preferences and objective assessments of circadian sleep and activity patterns are needed. Perhaps the ongoing works utilizing digital phenotyping techniques will help disentangle the links between circadian patterns and mental health and deliver bench to bedside solutions of chronobiologically-informed real-world clinical practice (Anmella et al., 2023).

As of now, it seems necessary to stress the importance to further research the role of chronobiological variables to mental health and promote lifestyle interventions focused on circadian alignment as both preventive and treatment strategies. Simple and cost effective treatments such as regulated sleep schedules, maintenance of sleep hygiene, controlled timing of food and caffeine or drug intake as well as light-therapy are too often overlooked or undermined, but can offer powerful interventions to promote the well-being of people with mental health issues.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Anna Julia Krupa reports a relationship with Angelini Pharma Poland that includes: consulting or advisory, funding grants, speaking and lecture fees, and travel reimbursement. Anna Julia Krupa reports a relationship with Lundbeck Poland that includes: travel reimbursement. Anna Julia Krupa reports a relationship with Swixx Biopharma Sp. z o.o. that includes: travel reimbursement. Anna Julia Krupa reports a relationship with Gedeon Richter Poland that includes: travel reimbursement. Anna Julia Krupa reports a relationship with Sandoz Polska Sp z oo that includes: travel reimbursement. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Handling Editor: Prof. A. Meyer-Lindenberg