Chronotype and Health: The Role of Moderators and Mediators in Shaping Outcomes

Yogita Kalra; Prabhjyot Kour

doi:10.33069/cim.2025.0007

Chronobiol Med > Volume 7(2); 2025 > Article

Kalra and Kour: Chronotype and Health: The Role of Moderators and Mediators in Shaping Outcomes

Review Article

Chronobiology in Medicine 2025;7(2):60-69.

Published online: June 27, 2025

DOI: https://doi.org/10.33069/cim.2025.0007

Chronotype and Health: The Role of Moderators and Mediators in Shaping Outcomes

Yogita Kalra

, Prabhjyot Kour

Department of Psychology, Lovely Professional University, Phagwara, Punjab, India

Corresponding author: Yogita Kalra, MA, Department of Psychology, Lovely Professional University, Phagwara, Punjab, New Delhi-110018, Inida.
Tel: 91-9818717237, E-mail: sisteryogita@yahoo.com

Received February 11, 2025 Revised May 11, 2025 Accepted May 18, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Chronotype, an individual’s natural preference for activity and alertness at certain times of day, has significant implications for mental, physical, and academic health. This study investigates the relationship between chronotype and health, emphasizing the impact of morning, evening, and intermediate chronotypes on mental and physical well-being. This narrative review explores the multifaceted effects of chronotype, focusing on how various outcomes (physical, mental, academic) are shaped by mediating and moderating mechanisms such as sleep disturbances, circadian misalignment, social jetlag, lifestyle and several biological, psychological, and social factors—including genetic predispositions, age, gender, personality traits, environmental light exposure, and cultural norms. The findings indicate that individuals with an evening chronotype are more prone to mental health challenges, including depression, anxiety, and substance use, as well as physical health concerns like musculoskeletal issues chronic pain, gastrointestinal, metabolic and cardiovascular issues These moderators and mediators dynamically interact to influence vulnerability or resilience across different chronotype profiles. A conceptual flow model is presented to illustrate these pathways and highlight key areas for personalized intervention. Misalignment with societal schedules may also adversely impact Academic and cognitive functioning. Intermediate types exhibit more flexible sleep-wake patterns and fewer health-related issues. The study highlights the importance of personalized interventions—such as tailored sleep hygiene, light therapy, and flexible schedules—to address chronotype-specific health concerns. Future longitudinal research is recommended to elucidate these relationships further.

Keywords: Chronotype; Mental health; Metabolic risk; Circadian misalignment; Mediators; Moderators; Social jetlag; Health outcomes

INTRODUCTION

The relationship between an individual’s chronotype, or the natural preference for morning or evening wakefulness, and their overall health is a fascinating area of study that has garnered significant attention in recent years. Chronotype is a reflection of the underlying circadian rhythms that govern many physiological processes, and mounting evidence suggests that misalignment between these rhythms and our daily behaviors can have profound implications for various aspects of health [1].

Chronotype refers to an individual’s natural inclination toward the timing of daily periods of activity and rest, largely dictated by their internal circadian clock. It refers to the idea that individuals differ in the time of day when they perform optimally. It manifests as a preference for morning or evening activities, commonly described along a spectrum from “morningness” to “eveningness” [2-4]. Morning types, often called “larks” or “early birds,” tend to wake up early, feel most alert in the early part of the day, and go to bed early. In contrast, evening types, known as “owls,” or “night people,” prefer to wake up later, feel most energetic in the afternoon or evening, and go to bed late [2]. Chronotype can be defined as an expression or proxy for circadian rhythms of varied mechanisms, for example, in body temperature, cortisol secretion, cognitive functions, eating, and sleeping patterns. It is influenced by a range of internal (e.g., genetics) and external factors (e.g., light exposure), and has implications for health and well-being [5].

The brain’s suprachiasmatic nucleus, located in the hypothalamus, acts as the circadian master coordinator, responding to environmental light cues, known as “zeitgebers,” and influencing various sleep timing preferences that define chronotype [6,7]. Chronotype is considered to constitute the phase of entrainment (Ψ) of an individual to the external light-dark cycle [2].

Chronotype has been consistently associated with various health outcomes and noncommunicable medical conditions [1,8-13]. A significant factor linking chronotype to health is circadian disruption or misalignment, which occurs when an individual’s internal biological clock is out of sync with external demands, such as irregular work schedules or social timing [11,14]. This mismatch, often termed social jetlag, when related to the difference between biological and social time [15,16], is particularly problematic for evening chronotypes forced into early schedules or for morning types working night shifts [8]. Circadian disruption is considered a central element in the development of shift work-related pathologies [17,18] and has been associated with serious health issues, including an increased risk of metabolic disorders like obesity and type 2 diabetes, cardiovascular disease, certain cancers, irritable bowel syndrome (IBS), and poorer mental health outcomes such as depression and emotional disturbance [11-13,19-22].

While the associations between chronotype, circadian misalignment, and negative health outcomes are well-documented, the relationship is not always direct. Various factors can influence these associations, acting either as mediators that explain the pathway through which chronotype or misalignment affects health, or as moderators that affect the strength or direction of this relationship [11,23,24]. For instance, emotional disturbance and vulnerability to insomnia have been shown to mediate the link between evening chronotype and poor subjective sleep quality [24].

This article aims to explore the intricate ways in which moderators and mediators shape the link between an individual’s chronotype and their health outcomes. By investigating these mediating and moderating pathways, we can gain a more comprehensive understanding of why certain chronotypes are associated with specific health risks and under what conditions these associations are most pronounced (Figure 1).

METHODOLOGY

This article is a narrative review aimed at exploring the relationship between chronotype and health outcomes, with a focus on the mediating and moderating variables that influence this association. A thematic synthesis approach was used to identify and organize relevant literature across domains such as mental health, metabolic and cardiovascular function, sleep, and academic performance.

Relevant peer-reviewed articles were sourced through manual and electronic searches of major academic databases including Scopus, PubMed, PsycInfo, Google Scholar, and ScienceDirect. Search terms included combinations of: chronotype, morning type, evening type, circadian rhythm, mental health, physical health, social jetlag, sleep disturbances, mediator, and moderator. Articles were selected based on relevance to the conceptual focus of chronotype and its health implications, rather than through a systematic or exhaustive protocol.

Studies included were primarily human-based and written in English, covering both observational, cross-sectional, and review studies. The review did not apply a strict inclusion or exclusion criterion, allowing for a broader exploration of findings across disciplines. Findings were then grouped into major thematic categories—mediators, moderators, and health outcomes—to support the construction of an integrative conceptual framework.

Data synthesis and limitations

The data were synthesized using a thematic approach, wherein findings from diverse disciplines were grouped under conceptual categories aligned with the review’s aim—namely, the mediating pathways (e.g., sleep disturbances, lifestyle behaviors) and moderating variables (e.g., age, gender, genetics) that influence the relationship between chronotype and health. This thematic organization enabled a multidimensional interpretation of how chronotype affects mental, physical, and academic outcomes.

However, as a narrative review, this article is subject to certain limitations. The selection of studies was not guided by a predefined protocol or systematic inclusion criteria, which may introduce selection bias. Additionally, the integration of findings across heterogeneous study designs (e.g., cross-sectional, longitudinal, and interventional) limits the ability to draw causal inferences. Despite these limitations, this approach allows for a broad and integrative understanding of chronotype-related health dynamics and supports hypothesis generation for future empirical research.

UNDERSTANDING CHRONOTYPE

Chronotype refers to an individual’s natural preference for the timing of daily activities—especially sleep and alertness—and is typically classified as morning, evening, or intermediate. These preferences reflect the phase of an internal circadian rhythm and are influenced by biological, environmental, and social factors [3,5,25].

At the biological level, chronotype is influenced by circadian clock genes such as PER3 and CLOCK, which regulate sleep-wake cycles, hormone secretion, and body temperature rhythms [26-28]. These intrinsic rhythms interact with external cues—light exposure, work schedules, cultural norms—to determine chronotype expression.

Assessment methods include subjective tools like the Morningness–Eveningness Questionnaire (MEQ), Composite Scale of Morningness (CSM), and Munich ChronoType Questionnaire (MCTQ), and objective tools such as actigraphy and dim light melatonin onset (DLMO). While subjective questionnaires capture personal preference and social timing, objective methods assess physiological rhythms and real-world behavior [25,29-31].

Chronotype is also dynamic across the lifespan, shifting toward eveningness during adolescence and back toward morningness in older adulthood, highlighting its developmental and contextual nature [26,32-34].

An integrative model illustrating the biological, environmental, and assessment components of chronotype is presented in Figure 2, which highlights the key influences and tools used to evaluate circadian preference in individuals.

MEDIATORS BETWEEN CHRONOTYPE AND HEALTH OUTCOMES

The relationship between chronotype and various health outcomes is not linear but is shaped by several mediating factors that operate across biological, behavioral, and environmental levels. Mediators are variables that explain the mechanism or pathway through which chronotype influences physical, mental, or academic outcomes. This section integrates findings from chronobiology, behavioral medicine, and sleep science to identify and contextualize key mediators in the chronotype–health relationship.

Evening chronotypes are disproportionately affected by sleep disturbances, circadian misalignment, and social jetlag, which result from the chronic mismatch between internal biological timing and externally imposed schedules [35,36]. These disruptions often lead to irregular sleep-wake patterns, especially among shift workers or students with late-night screen exposure, ultimately influencing cognitive function, emotional regulation, and physiological health [37,38]. Furthermore, maladaptive lifestyle behaviors such as nocturnal eating, sedentarism, and inconsistent routines are more prevalent in evening types, contributing to metabolic and cardiovascular risk [39,40]. Emotional dysregulation, stress reactivity, and impaired coping styles also mediate the link between chronotype and mental health outcomes such as depression, anxiety, and burnout [41,42]. In academic and occupational contexts, early work or school start times create a persistent misalignment for evening chronotypes, leading to sleep loss, poor performance, and reduced motivation [43,44]. These mediators are summarized in Table 1, which categorizes them by how they impact mental, physical, and academic domains.

MODERATORS OF CHRONOTYPE–HEALTH RELATIONSHIPS

While mediators explain how chronotype affects health, moderators determine when, for whom, or to what extent these effects occur. A variety of biopsychosocial factors moderate the link between chronotype and health outcomes, either amplifying or buffering the risks associated with circadian misalignment. Age is a well-documented moderator; for example, adolescents are more vulnerable to academic and emotional challenges when chronotype and school timing conflict, whereas older adults often shift toward morningness and show fewer adverse effects [33,36]. Gender and hormonal cycles—such as those related to menstruation or menopause—modulate how chronotype influences sleep quality and mood [45-48]. Genetic factors, especially polymorphisms in PER3 or CLOCK genes, affect baseline chronotype expression and adaptability [28,39,49]. Environmental and cultural factors, such as daylight exposure and social timing norms, further influence the severity of chronotype-health relationships, especially in evening types [50-52]. Personality traits like neuroticism and conscientiousness affect stress reactivity and behavioral regulation, shaping how individuals respond to circadian misalignment [53-55]. Importantly, workplace and academic flexibility serve as protective moderators by allowing chronotype-congruent scheduling, thereby reducing the effects of social jetlag and sleep debt [44,56,57]. Lastly, emerging findings suggest that gut microbiome rhythms may interact with chronotype to impact metabolic and immune function [58].

These moderators are summarized in Table 2, which provides an integrative overview of how these moderators shape or affect the relation between chronotype–health dynamic.

PRACTICAL IMPLICATIONS

Understanding chronotype and its influence on health has valuable real-world applications across clinical, educational, and occupational settings. Tailoring interventions and policies to support individual circadian preferences can improve well-being, productivity, and long-term health outcomes.

Personalized sleep hygiene and behavioral interventions

Sleep hygiene recommendations often assume a one-size-fits-all approach, but chronotype-informed strategies are likely to be more effective. For instance, evening chronotypes may benefit from gradual sleep phase advancement techniques, controlled evening light exposure, and early-morning bright light therapy to improve circadian alignment [59]. Behavioral counseling should consider individuals’ natural rhythms when setting goals for sleep, activity, and substance use. Moreover, interventions targeting lifestyle behaviors—such as timed meals, exercise routines, and reduced nighttime screen use—are especially relevant for evening types, who are more prone to unhealthy habits [39,60]. These personalized strategies not only improve sleep quality and mental health but may also mitigate risks for metabolic and cardiovascular disease. Integrating chronotype screening into behavioral therapy, cognitive behavioral therapy for insomnia, and psychiatric treatment can enhance outcomes for individuals with chronotype-related vulnerabilities [61].

Chronotype-informed clinical and school/workplace scheduling

Rigid work and school schedules disproportionately affect evening chronotypes, leading to chronic sleep deprivation, poor academic/work performance, and mood disturbances [43]. Chronotype-informed scheduling—such as flexible work hours, delayed school start times, and shift matching based on circadian preference—has been shown to improve sleep duration, reduce social jetlag, and boost productivity [57].

In healthcare, personalized chronotherapy—timing treatment in accordance with circadian phase—has demonstrated success in optimizing medication efficacy and minimizing side effects in conditions like hypertension, asthma, and cancer [62]. Hospitals, schools, and businesses can incorporate circadian-informed policies to promote employee and student health, reduce burnout, and improve cognitive functioning.

Implementing chronotype-informed shift scheduling can significantly reduce circadian misalignment, especially for evening chronotypes who are more susceptible to adverse health outcomes when assigned early shifts. Moderating factors such as workplace flexibility, chronotype adaptability, and environmental conditions play a crucial role in determining the effectiveness of such scheduling strategies.

Importance of public awareness and chronotype screening

Despite its wide-ranging implications, chronotype is rarely addressed in standard health assessments. Raising public awareness about chronotype and its relevance can empower individuals to make informed choices about their sleep, lifestyle, and productivity. Incorporating chronotype screening tools like the MEQ or MCTQ in general health check-ups, school wellness programs, and workplace assessments can help identify at-risk individuals and inform tailored interventions [5,25].

Educational campaigns should emphasize the biological basis of chronotype to reduce stigma (e.g., “lazy” late risers) and promote acceptance of circadian diversity in policy-making. By normalizing individual variation in sleep timing and advocating for structural flexibility, society can better support mental and physical health across the chronotype spectrum.

FUTURE DIRECTIONS

Despite growing recognition of chronotype as a determinant of health, significant gaps remain in the empirical literature. Addressing these limitations will require methodologically rigorous, longitudinal, and intervention-based studies that can better establish causality and refine personalized interventions.

Emphasis on longitudinal and intervention studies

Most current research on chronotype is cross-sectional, limiting causal interpretations. Future studies should adopt longitudinal designs to assess how chronotype-related health risks evolve over time and across life stages. For example, tracking individuals from adolescence into adulthood could reveal how chronotype shifts affect long-term mental and physical health trajectories. Moreover, controlled intervention studies—including chronotherapy, flexible scheduling trials, and behavioral programs tailored to chronotype—are needed to evaluate which strategies effectively reduce misalignment and improve outcomes [63].

Need for chronotype-inclusive health research

There is a growing need for chronotype to be included as a standard variable in health, behavioral, and clinical research. Despite evidence linking eveningness to greater vulnerability to depression, metabolic dysfunction, and social jetlag, chronotype is rarely assessed in large-scale epidemiological studies or clinical trials [41]. Standardized screening tools such as the MEQ or MCTQ should be incorporated into psychological assessments, workplace wellness programs, and public health surveys to allow for risk stratification and personalized interventions.

In addition, diverse populations must be represented to understand how cultural, environmental, and occupational factors interact with chronotype across contexts.

Integration with wearable technology and real-time data

With advances in wearable technology (e.g., actigraphy, sleep trackers, circadian rhythm monitors), there is a unique opportunity to gather real-time, ecologically valid data on sleep-wake behavior, light exposure, and activity patterns. These tools can help estimate chronotype more accurately and continuously monitor circadian alignment. Integration of wearable-derived data into clinical decision-making and workplace policies could allow for dynamic, individualized circadian health plans [64-66]. The convergence of chronobiology with digital health platforms, machine learning, and personalized health algorithms may transform how we assess and address circadian-related health risks.

Chronobiology-informed workplace strategies to enhance well-being and performance

To enhance employee well-being and performance through chronobiology-informed strategies, several workplace interventions can be implemented. First, aligning shift schedules with individual chronotypes can significantly reduce fatigue, improve performance, and enhance job satisfaction [11,67,68]. Exposure to natural light and the optimization of artificial lighting can help regulate circadian rhythms, thereby improving alertness, sleep quality, and overall mood [69,70]. The introduction of short, controlled naps in high-risk jobs, along with designated rest areas, can boost mental clarity and reduce errors [71]. Flexible work arrangements—such as remote options, staggered hours, or compressed workweeks—support better work-life balance and prevent burnout [64,72]. Additionally, comprehensive wellness initiatives that include education on sleep hygiene, ergonomic practices, nutrition, and mindfulness can promote overall health and resilience [73,74]. Fatigue mitigation techniques, including regular breaks, balanced task allocation, and fatigue-monitoring tools, can prevent exhaustion and improve workplace safety [63]. Nutritional support, particularly for night-shift workers, through scheduled meals and healthy food availability, supports metabolic health and sustained energy [73]. Scheduling critical tasks during peak cognitive hours can further enhance productivity and decision-making [65]. Technology can also play a role, with AI-assisted scheduling tools, biometric monitoring, and sleep tracking apps helping to align work demands with biological rhythms [39]. Finally, psychological support through counseling, stress-relief facilities, and mental wellness programs can mitigate stress and address circadian-related challenges [66]. These approaches align with the framework proposed in earlier work by Kalra and Kour [63], which emphasizes the integration of chronobiological principles into organizational health strategies.

CONCLUSION

Chronotype plays a pivotal role in shaping individual health trajectories by influencing patterns of sleep, behavior, emotional regulation, and physiological functioning. As demonstrated throughout this review, the relationship between chronotype and health is mediated by modifiable factors such as sleep hygiene, circadian alignment, lifestyle behaviors, and environmental exposure, while also being moderated by non-modifiable elements like age, genetics, hormonal cycles, and personality traits.

Evening chronotypes appear particularly vulnerable to adverse outcomes due to chronic misalignment between their biological clock and the timing demands of society—especially rigid school, work, and social schedules. These findings underscore the importance of recognizing chronotype not merely as a preference, but as a biologically rooted trait with profound implications for mental, physical, and academic well-being.

To promote better health across the chronotype spectrum, there is an urgent need to align biological time with lifestyle design, institutional policies, and environmental conditions. Chronotype-aware public health messaging, clinical care, and workplace or educational reforms hold promise for reducing circadian misalignment and fostering resilience. As science advances, integrating chronotype into personalized health strategies will be a critical step toward achieving more equitable, effective, and sustainable health outcomes.

NOTES

Conflicts of Interest

The authors have no potential conflicts of interest to disclose.

Availability of Data and Material

Data sharing not applicable to this article as no datasets were generated or analyzed during the study.

Author Contributions

Conceptualization: Yogita Kalra. Data curation: Yogita Kalra. Formal analysis: Yogita Kalra. Investigation: Yogita Kalra. Methodology: Yogita Kalra. Project administration: Yogita Kalra. Resources: Yogita Kalra. Supervision: Prabhjyot Kour. Validation: Yogita Kalra. Visualization: Yogita Kalra. Writing—original draft: Yogita Kalra. Writing—review & editing: Yogita Kalra.

Funding Statement

None

Acknowledgments

The author extends sincere gratitude to the researchers and contributors in the field of chronobiology whose valuable findings have informed this perspective. Appreciation is also due to the editorial team of Chronobiology in Medicine for their continued efforts in disseminating critical knowledge on circadian health. Lastly, the author acknowledges the institutional support provided by Lovely Professional University, Phagwara, Punjab, India, which enabled the completion of this work.

Figure 1.

Conceptual framework illustrating the relationship between chronotype and health outcomes through mediators and moderators. This figure depicts the influence of chronotype on mental, physical, and academic health outcomes. Mediating factors (e.g., sleep problems, social jetlag, lifestyle behaviors) explain how chronotype affects these outcomes, while moderating variables (e.g., age, gender, genetics, environmental and personality factors) influence the strength or direction of these relationships. Created using draw.io (diagrams.net).

Figure 2.

Biopsychosocial and assessment components of chronotype. This figure illustrates the multidimensional nature of chronotype, integrating biological, social, and environmental influences, along with subjective and objective tools used for chronotype assessment. It highlights the interplay of circadian clocks, genetic predispositions (e.g., PER3), social jetlag, and lifestyle factors in shaping morning, intermediate, and evening preferences. MEQ, Morningness–Eveningness Questionnaire; CSM, Composite Scale of Morningness; MCTQ, Munich ChronoType Questionnaire; DLMO, dim light melatonin onset.

Table 1.

Key mediating variables linking chronotype to mental, physical, and academic health outcomes

Mediator	Description/How it mediates	Associated health outcomes	Citations
Sleep problems	Insomnia, fragmented sleep, poor sleep quality, delayed sleep phase—more common in evening types due to misalignment with societal demands	Depression, anxiety, fatigue, impaired alertness, metabolic dysfunction, and reduced cognitive performance	[61,75-80]
Sleep duration and timing	Shortened or irregular sleep due to early obligations and late chronotype preferences; Difficulties initiating and maintaining sleep, poor sleep quality, delayed sleep phase, and reduced sleep duration; These issues are frequently associated with evening chronotypes and the demands of shift work that conflict with natural sleep patterns.	Reduced academic performance, mood instability, metabolic disease, and cardiovascular risk	[80,81]
Circadian misalignment	Mismatch between biological clock and social schedule; chronic misalignment termed “social jetlag”	Mood disorders, metabolic syndrome, obesity, cardiovascular disease, and cancer risk	[1,9,82,83]
Social jetlag	Weekend vs. weekday timing discrepancy; evening types often struggle with early schedules. The discrepancy between an individual’s internal biological clock (chronotype) and the timing of their social and work schedules. Adapting to this mismatch requires daily effort and can disrupt natural physiological rhythms.	Poor well-being, depression, diabetes, metabolic syndrome; Worse well-being, increased depression, general health complaints, detrimental effects of shift work, reduced performance, alertness, and mood; Long-term misalignment is linked to increased risk of chronic diseases such as obesity, diabetes, cardiovascular problems, and is associated with potential carcinogenesis (e.g., shift work and breast cancer).	[35,84,85]
Irregular sleep-wake patterns	Inconsistent timing due to work demands, screen time, or social habits, especially in evening types	Sleep deprivation, impaired immunity, and psychological distress	[37,86,87]
Shift work	Disruption of circadian rhythms by night or rotating shifts, misaligned with most chronotypes	Obesity, cardiovascular diseases, insomnia, anxiety, and poor metabolic control	[20,70,88,89]
Screen time before bed	Artificial light exposure delays melatonin onset and impairs sleep initiation.	Delayed sleep phase, reduced melatonin, and insomnia	[90-92]
Work/school start times	Fixed early schedules conflict with evening chronotypes, reducing total sleep time.	Sleep deprivation, fatigue, and poor academic performance	[43,44,93]
Mood instability	Emotional lability in evening types due to circadian misalignment and insufficient rest	Depression, anxiety, and suicidality	[41,85,94]
Stress and coping styles	Evening types are more likely to use maladaptive coping (e.g., avoidance), while morning types show better resilience.	Chronic stress, depression, and burnout	[41,42,95]
Lifestyle behaviors	Evening types show delayed eating, poor diet quality, and lower physical activity.	Obesity, diabetes, metabolic syndrome, cardiovascular disease; increased body mass, body mass index, obesity, cardiovascular and gastrointestinal problems, metabolic diseases (like type 2 diabetes), and increased cardiovascular risk factors (e.g., LDL/HDL cholesterol ratio, plasma triacylglycerol)	[39,40,96,97]

LDL, low-density lipoprotein; HDL, high-density lipoprotein

Table 2.

Moderating variables influencing the relationship between chronotype and health outcomes

Moderator	Description/Moderating role	Affected outcomes	Citations
Age	Chronotype changes with age—youth favor eveningness, older adults shift to morningness—moderating sleep patterns, emotional regulation, and performance. Age, together with circadian desynchronization, is associated with elevated body mass index. Age itself may generally influence sleep duration and quality. Previous studies using different instruments did suggest that age had a differential effect on shift-specific sleep.	Sleep quality, metabolic and mood disorders, and academic performance	[32,33,36]
Gender	Men tend toward eveningness more than women. Hormonal differences also moderate sleep needs, mood, and chronotype expression.	Depression, sleep quality, and cardiovascular and hormonal balance	[46,47,98]
Hormonal cycles	Menstrual cycles, menopause, and pregnancy influence circadian phase and vulnerability to sleep and mood disturbances, particularly in evening chronotypes.	Insomnia, depression, and fatigue	[54,61,99-101]
Genetic factors	Variants in circadian genes (PER3, CLOCK, BMAL1) influence baseline chronotype and susceptibility to misalignment and health risks. Specific gene polymorphisms in circadian and melatonin pathways can interact with environmental exposures like night shift work to influence health outcomes such as breast cancer risk. Since chronotype is linked to genetic variables, this represents a form of genetic moderation on the impact of circadian disruption (related to chronotype and shift work) on health.	- Sleep disorders, circadian adaptability, and psychiatric risk	[39,49,102]
Genetic factors		- Cancer risk	[39,49,102]
Environmental factors	Light exposure, geographical latitude, climate, and noise affect circadian rhythms and influence how strongly chronotype impacts health.	Circadian misalignment, seasonal affective symptoms, and sleep quality	[16,74,91,103,104]
Personality traits	Neuroticism, conscientiousness, and extraversion shape behavior, stress reactivity, and health outcomes across chronotype types.	Coping strategies, mental health, and substance use	[42,53]
Chronotype adaptability	The degree to which individuals modify behaviors (e.g., sleep timing, coping) in response to circadian challenges influences their resilience.	Shift work tolerance, emotional regulation	[41,105,106]
Work and academic flexibility	Flexible scheduling may buffer the negative effects of social jetlag for evening types, reducing misalignment and improving outcomes.	Sleep duration, academic/work performance, and psychological stress	[44,56,57,95]
Cultural and societal norms	Societies that prioritize early rising or rigid scheduling amplify stress for evening types. Cultural attitudes about rest and productivity shape behavioral adaptation.	Social stress, academic achievement, and well-being	[50,107,108]
Microbiome rhythms	Emerging research links circadian patterns in gut microbiota to metabolic outcomes, which may be moderated by chronotype.	Gut health, obesity, and inflammation	[58]

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