Domino effect of evening chronotype: How chronotype topples adolescent mental health through sleep and social functioning

Abstract

This commentary elucidates the novel sequential mediation pathway (evening chronotype - sleep quality - social functioning - mental health) identified by Zhao et al, framing it as a coherent “domino effect” that links biological predisposition to psychosocial outcomes in adolescents. The analysis extends beyond summary to critically examine how this model advances the theoretical understanding of circadian-related psychopathology by specifying previously understudied mechanisms. The findings necessitate a paradigm shift in intervention design - away from correcting chronotype itself and toward targeting the malleable mediators of sleep and social functioning. A “chrono-health” approach is proposed, integrating sleep hygiene with social-skills training within ecologically valid settings such as schools and communities. Finally, the implications of these results are discussed for future longitudinal and experimental research, as well as for policy-making aimed at creating supportive, timing-friendly environments for neurodiverse adolescents.

Key Words: Evening chronotype; Domino effect; Sleep; Social functionging; Mental health; Adolescents

Core Tip: Zhao et al identified a mediating mechanism through which an evening-type circadian preference affects mental health via a sequential pathway involving sleep quality and social functioning. Their findings indicate that intervention strategies should focus on modifiable factors such as sleep hygiene and social competence, rather than enforcing conformity to rigid sleep-wake schedules. Further longitudinal research is warranted to corroborate these causal pathways and to develop evidence-based interventions integrating sleep management with social skills training.

TO THE EDITOR

Adolescence represents a critical period of physical and neurobiological development[1-3]. This stage is characterized by reorganization of the circadian system - a shift that induces a pronounced delay in sleep-wake patterns. This delay is commonly quantified using psychometric instruments such as the Morningness-Eveningness Questionnaire, with individuals scoring ≤ 41 on the standard scale being classified as having an evening chronotype[4,5]. A study found that the prevalence of evening chronotype among adolescents was 70%[6]. This evening chronotype frequently conflicts with socially imposed schedules - such as early school start times - resulting in chronic misalignment that has been associated with increased mental health risks[7,8]. Numerous studies have established associations between evening chronotype and internalizing symptoms including depression and anxiety[9-11]. Cross-sectional evidence indicates that adolescents endorsing an evening chronotype display elevated anxiety symptomatology relative to their morning-type or intermediate-type counterparts[12]; however, the putative mediating roles of sleep quality and social functioning in this chronotype-anxiety nexus remain to be empirically elucidated. This conceptual gap has hindered the development of targeted, theory-informed interventions.

Zhao et al[13] in 2025 offers a significant advance by explicitly modeling these mediating pathways. The study participants (n = 381) were Chinese adolescents (mean age = 14.34 ± 1.21 years; 38.1% girls). Participants had an average educational duration of 8.73 ± 1.15 years. In this study, the Cronbach’s α for the Pittsburgh Sleep Quality Index was 0.83. Using a chained-mediation analysis, they demonstrate that evening chronotype contributes to mental health difficulties through a sequential process. This indirect pathway accounted for 69.3% of the total association with depressive symptoms and 79.6% of the total association with anxiety symptoms, indicating that the vast majority of the observed relationship is explained by this mechanistic cascade. First via compromised sleep quality, and subsequently through diminished social functioning. By moving beyond bivariate associations, they uncover a dynamic mechanism spanning behavioral and social domains, thereby providing a methodological framework for future research in circadian neuroscience and developmental psychopathology.

In this commentary, we evaluate the contributions of Zhao et al[13] along three key dimensions. First, we examine the methodological innovations that enable the capture of cascading effects resulting from circadian misalignment. Second, we discuss how these findings reframe clinical perspectives - shifting the focus from altering chronotype itself toward targeting modifiable factors, specifically sleep quality and social functioning. Finally, we integrate these insights to propose a forward-looking research agenda that emphasizes longitudinal, experimental, and policy-oriented studies. Through this appraisal, we aim to support the field’s progression from descriptive phenomenology toward mechanistic explanation and ultimately, precision interventions tailored to adolescents’ circadian characteristics.

METHODOLOGICAL STRENGTHS AND LIMITATIONS

Zhao et al[13] adopt an analytically rigorous design whose principal asset is the deployment of a serial-mediation framework. By simultaneously estimating multiple indirect pathways, the model elucidates the micro-process through which evening chronotype exerts distal effects on adolescent emotional adjustment via the ordered sequence of deteriorating sleep quality and concomitant erosion of social functioning. Bias-corrected bootstrapping corroborated a significant aggregate indirect effect and further decomposed it into three orthogonal routes: (1) An exclusive path operating through sleep quality; (2) An independent path mediated solely by social functioning; and (3) A chained path in which compromised sleep quality propagates risk by undermining subsequent social competence. This specification transcends traditional single-mediator paradigms and furnishes a nuanced mechanistic account that positions social functioning as both a substantive mediator and an obligatory relay through which sleep perturbations crystallize into affective symptomatology.

Several constraints qualify these inferences. Cross-sectional architecture, although consistent with temporal logic implied by mediation, cannot adjudicate reciprocal causality. The possibility of reverse causality should be acknowledged. Extant longitudinal evidence indicates that depressive symptomatology prospectively predicts both sleep fragmentation[14] and interpersonal withdrawal[15], rendering reverse directionality plausible. Second, mono-method reliance on self-report inventories inflates shared-source variance and renders coefficients susceptible to mood-congruent recall and social-desirability distortions. The reliance on self-report measures introduces the potential for common method bias. However, this concern was partially mitigated by a Harman’s single-factor test, which revealed that the first unrotated factor accounted for 29.2% of the total variance, falling below the critical threshold of 40%. This suggests that common method variance is unlikely to be a severe threat to the interpretation of the findings. Objective metrics (e.g., actigraphy, polysomnography, sociometric nominations) and multi-informant protocols are imperative to bolster construct validity. Furthermore, while the authors controlled for key demographic variables such as age and gender, the omission of socioeconomic status as a covariate represents a potential confounding influence. Given the established links between socioeconomic status, sleep quality, and mental health outcomes, future replications should incorporate this critical variable to rule out its spurious effects. Finally, the geographically circumscribed, single-country sample attenuates external validity; invariant pathway structures must be demonstrated across divergent cultural chronotypes and scholastic schedules before policy translation is warranted.

In aggregate, Zhao et al[13] instantiates a theoretically innovative yet provisional mechanism. While the application of bootstrapped mediation analysis is a strength, a more critical appraisal reveals potential limitations. The model assumes linear relationships between variables, which may not fully capture complex, non-linear dynamics in adolescent development. Furthermore, the reliance on a single, albeit large, sample raises questions about the stability (e.g., bootstrap confidence intervals) and reproducibility of the path coefficients across different populations. Their limitations delineate a programmatic agenda: Prospective, multi-wave designs that establish temporal precedence; multimodal measurement batteries that disentangle method from substantive variance; explicit inclusion of socioeconomic and other key confounding variables in analytical models; and culturally heterogeneous cohorts to test the boundary conditions of the hypothesized chronotype - sleep - social functioning -psychopathology cascade.

CLINICAL AND ACADEMIC IMPLICATIONS

Theoretically, Zhao et al[13] move beyond bivariate associations to model a multilevel bio-behavioural-social cascade, demonstrating how evening chronotype translates into psychopathology through sequential declines in sleep homeostasis and social competence. Their work provides robust empirical grounding for the “social jetlag” hypothesis from chronobiology. This hypothesis posits that the chronic misalignment between an individual's endogenous circadian rhythm and socially imposed timetables acts as a psychosocial stressor that impairs well-being[16,17]. While the hypothesis identifies the state of misalignment as the risk factor, the specific biopsychological pathways through which it exacts its toll have remained somewhat speculative. Herein lies the key contribution of Zhao et al’s study[13]. By identifying the sequential pathway of sleep quality deterioration followed by social dysfunction, their model specifies the mechanistic route through which social jetlag translates into affective consequences. This pathway is supported by established biological mechanisms: The evening chronotype is characterized by a delayed melatonin rhythm, directly disrupting sleep initiation and continuity[18,19]. The resulting sleep deprivation then impairs the functional connectivity between the prefrontal cortex (critical for emotional regulation and social cognition) and the amygdala (the core neural substrate of threat processing). This neurobiological disruption provides a plausible substrate for the observed behavioural dysregulation (e.g., increased anxiety, poor impulse control) and subsequent social impairment. Thus, the identified dual-mediation pathway effectively bridges a core biological predisposition (eveningness) with distal clinical outcomes through proximal neurobehavioral mechanisms. By integrating previously fragmented determinants - chronotype, sleep, and interpersonal functioning - into a coherent biopsychosocial model, the study provides a predictive framework that highlights modifiable intervention targets and marks a paradigm shift from descriptive to mechanistic research. These theoretical and mechanistic insights are strongly corroborated by recent empirical evidence. For instance, a recent investigation revealed that adolescents with an evening chronotype exhibited significantly shorter sleep duration, greater social jet lag, and markedly higher levels of daytime sleepiness, insomnia, anxiety, and depressive symptoms[20]. Furthermore, the broader implications of social jetlag are illustrated by a large-scale study of 64029 Brazilian adolescents, which demonstrated that health-risk behaviors - including breakfast skipping, alcohol consumption, and increased screen time - were significantly associated with a higher prevalence of social jet lag[21].

Clinically, these findings advocate a transition from corrective to accommodative interventions. The demonstration of full mediation suggests that neutralizing the adverse effects of evening chronotype - rather than eliminating the preference itself - by targeting sleep and social functioning offers a more viable treatment strategy. This supports a three-tiered “chrono-health” framework comprising: (1) Chrono-fit: Personalized scheduling and light therapy to align endogenous rhythms with environmental demands; (2) Sleep enablement: Sleep timing adjustment guided by phase-response curves and cognitive-behavioural therapy to improve sleep quality and daytime functioning; and (3) Social support restructuring: Forming chronotype-concordant social groups and asynchronous communication channels to reduce isolation due to schedule differences. Empirical support for the latter two components is particularly robust. Previous studies have demonstrated that electronically delivered cognitive behavioural therapy for insomnia - a key modality for sleep enablement - effectively improves sleep quality and alleviates co-occurring anxiety and depression[22]. Furthermore, the crucial role of social support is underscored by emerging evidence demonstrating that robust supportive ties with peers, extended family, and friends predict a reduced likelihood of sleep disturbances, even after controlling for baseline mental health status[23].

More broadly, this study calls for a systemic reconfiguration of adolescent mental health promotion toward evidence-based “chrono-friendly ecosystems”. This approach is supported by a growing body of literature demonstrating the effectiveness of structural modifications. For instance, delayed school start times - a core component of such ecosystems - have been shown to significantly increase sleep duration, improve academic performance, and reduce depressive symptoms among adolescents[24-26]. Specifically, these ecosystems would integrate: (1) Flexible school scheduling policies informed by chronobiological research; (2) Educational initiatives to reduce stigma associated with evening chronotype; (3) accessible after-school mental health services tailored to adolescents’ circadian rhythms; and (4) Coordinated home-school agreements that recognize individual sleep needs. This ecological framework not only promotes equitable development for evening-type adolescents but also represents a paradigm shift from deficit-oriented individual interventions toward inclusive, structurally supportive environments that respect neurobiological diversity.

RECOMMENDATIONS FOR FUTURE RESEARCH AND POLICY

Based on the chained mediation mechanism identified in the study and its methodological limitations, this commentary proposes the following specific recommendations for future research and policy-making.

First, methodologically, longitudinal follow-up designs with multiple time points are essential to elucidate temporal dynamics and causal ordering among variables. A minimum of three waves of data collection is specifically recommended, as this constitutes the fundamental requirement for testing the temporal precedence and dynamic relationships inherent in a chained-mediation model. This design allows researchers to examine, for instance, whether change in evening chronotype at Time 1 predicts subsequent change in sleep quality at time 2, which in turn leads to altered social functioning by time 3. The proposed six-month interval between assessments is theoretically and pragmatically justified. This duration is sufficiently long to capture meaningful developmental changes in sleep patterns, social adaptation, and emotional functioning during adolescence, while being short enough to reduce potential confounding from extraneous life events and cohort effects. This interval aligns with established practices in developmental and chronobiological research, balancing methodological rigor with practical feasibility in school-based longitudinal studies.

Second, with respect to measurement, diversified assessment tools should be employed to overcome the limitations of self-reported data. Objective measures - such as actigraphy for monitoring sleep duration and efficiency - and well-validated daytime functioning scales should be incorporated. Multi-informant data (e.g., teacher-reported social competence and parent-observed sleep behaviors) are also essential. A multi-method, multi-source approach can significantly improve the reliability, validity, and ecological relevance of findings, thereby offering a more robust basis for evaluating interventions.

Third, regarding research content, although existing studies suggest the importance of protective factors, further systematic examination of their role in the link between evening chronotype, sleep, and social functioning is needed, particularly in cross-cultural and multi-wave settings. Future research should investigate how individual characteristics (e.g., emotion regulation strategies, resilience) and environmental resources (e.g., family support, school climate) may buffer the negative effects of evening chronotype, which could reveal factors that disrupt the chain linking circadian preference to sleep impairment and social dysfunction. The use of moderated mediation analysis is particularly recommended to simultaneously test mediating mechanisms and protective moderators. Beyond mechanistic inquiry, future research must pivot toward designing and evaluating evidence-based interventions. Specifically, randomized controlled trials are urgently needed to test the efficacy of proposed strategies such as the “chrono-health” framework outlined above. These trials should not only assess outcomes at the individual level (e.g., improved sleep, reduced depressive symptoms) but also measure implementation success at the systemic level.

Forth, future research should incorporate objective physiological biomarkers to move beyond subjective reports and directly quantify circadian misalignment. Specifically, measuring the Dim Light Melatonin Onset would provide a gold-standard assessment of endogenous circadian phase, allowing for a precise calculation of the discrepancy between biological and social time (i.e., true social jetlag). Concurrently, assessing the Cortisol Awakening Response could illuminate the involvement of the hypothalamic-pituitary-adrenal axis, revealing the neuroendocrine stress mechanisms potentially linking circadian disruption to affective symptoms. The integration of such biomarkers will significantly strengthen the biological plausibility of the observed associations.

Looking ahead, integrating genetic predispositions into the model will provide a more comprehensive, individual-difference perspective. Future studies should consider incorporating polygenic scores for circadian rhythms and sleep regulation - aggregating risk variants in genes such as MTNR1B (involved in melatonin signaling) and CLOCK (a core circadian clock gene) - to examine gene × environment interactions. This approach could reveal why some evening chronotype adolescents are more vulnerable to the negative effects of social jetlag than others, ultimately paving the way for personalized prevention strategies targeting those at highest genetic and environmental risk.

The findings of Zhao et al[13] must be interpreted within the specific socio-cultural context of contemporary Chinese adolescence, a perspective that both enriches and potentially delimits the generalizability of the proposed model. The model’s potency may be particularly amplified in settings characterized by intense academic pressure and collectivistic social values. For instance, the stringent, early-morning school schedules pervasive in China likely exacerbate the social jetlag experienced by evening-type adolescents. Furthermore, in a culture that highly values academic achievement and social harmony, impaired social functioning resulting from sleep loss may carry greater detrimental consequences for self-esteem and psychological well-being than it might in more individualistic societies. Therefore, the mediating role of social functioning identified in this study might be especially salient in the Chinese context. Conversely, this cultural specificity necessitates caution when generalizing the findings. The strength of these pathways warrants empirical testing in cultures with different educational systems (e.g., later start times in some Western countries) and social expectations to determine the universal vs culture-bound aspects of the eveningness-psychopathology link.

From a policy perspective, education authorities should integrate sleep health education and social-emotional learning into standard curricula, with content and activities tailored to different developmental stages. Topics should include biological rhythm science, sleep hygiene, emotion regulation, and interpersonal skills to help students better understand and align with their own chronobiological characteristics. In addition, while proposing flexible school start times is theoretically sound, its implementation requires careful consideration of feasibility. Key barriers include logistical challenges for transportation systems, resistance from stakeholders accustomed to traditional schedules, and equity concerns regarding resource distribution. To enhance the translational impact of these findings, we propose a tiered intervention framework comprising three complementary approaches. At the ideal level, systemic reform involving delayed school start times would effectively align educational schedules with adolescent circadian biology. For more immediate implementation, a pragmatic intermediate step would introduce one flexible start day per week (e.g., Wednesday), providing regular circadian relief with minimal operational disruption. At the micro-level, readily deployable individual solutions such as 30-minute morning bright-light therapy sessions could offer rapid amelioration of circadian misalignment. This multi-tiered strategy provides a scalable pathway from feasible short-term adaptations to transformative long-term policy change, significantly strengthening the practical utility of the evidence-based recommendations.

Furthermore, a collaborative support system involving schools, families, and communities should be established. Education and health departments could partner to implement tiered screening and intervention protocols in schools, including regular sleep and mental health assessments. At-risk students - such as those exhibiting sleep problems or social difficulties - should receive individualized support. Parent education initiatives (e.g., through parent-school workshops) should also be offered to increase awareness of circadian rhythms and sleep health, enabling families to better support adolescents’ needs. For settings with limited resources (e.g., school counseling services), we recommend a targeted approach focused on the highest-risk subgroup. Individuals who meet both of the following criteria should be prioritized for intervention: (1) An evening chronotype (operationalized as an Morningness-Eveningness Questionnaire score ≤ 41); and (2) Poor sleep quality (operationalized as a Pittsburgh Sleep Quality Index global score > 5). This combination identifies adolescents who are not only biologically predisposed to circadian misalignment but are also already experiencing its negative functional consequence - impaired sleep. Focusing resources on this defined high-risk group ensures the most efficient and potentially impactful allocation of limited intervention capacities. Crucially, the effectiveness of any intervention will depend on the buy-in and competence of key stakeholders. Therefore, a parallel line of research should focus on developing and validating training modules for teachers and parents. These modules should educate adults on the neurobiological basis of evening chronotype, reduce stigma, and equip them with practical skills to support adolescents' sleep hygiene and social-emotional needs without conflating chronotype with laziness or poor discipline. Investigating the most effective methods for delivering this psychoeducation - whether through workshops, digital platforms, or embedded professional development - will be essential for successful real-world implementation.

Finally, large-scale multi-center collaborative studies should be encouraged. Research institutions and schools across diverse regions should conduct coordinated studies using unified protocols to examine cultural and regional variations in the chronotype-mental health relationship. Such efforts will not only enhance the generalizability of findings but also inform context-sensitive educational and health policies. It is recommended that funding bodies and education agencies establish special grants to support such collaborative projects.

CONCLUSION

Zhao et al[13] elucidated a dynamic mechanism through which circadian rhythms influence mental health via behavioral and social pathways by validating the chained mediating roles of sleep quality and social functioning between evening chronotype and mental health. This discovery not only advances a paradigm shift from correlational research to mechanistic exploration but also inspires a new intervention framework centered on “temporal health”. This approach moves away from correcting individual rhythms toward building a timing-friendly environment and achieves this by implementing multidimensional strategies - such as personalized sleep-wake adjustment, improved sleep quality, and optimized social support systems - to provide more inclusive and targeted mental health support for adolescents with diverse chronotypes. Future studies should refine this theoretical model through longitudinal designs and cross-cultural validation, while promoting the practical application of “timing-friendly” ecosystems via joint school- and community-based intervention trials, ultimately establishing an adolescent mental health promotion system that respects neurodiversity.