The relationship between negative life events and anhedonia among patients with major depressive disorder: chain mediation of insomnia and dysfunctional attitudes

Anhedonia has emerged as a core and transdiagnostic symptom in psychopathology, evident in a variety of psychological disorders such as depression, anxiety, and schizophrenia [1‐3]. Anhedonia is characterized by significantly reduced interest or enjoyment in nearly all activities for almost every day [4]. The prevalence of anhedonia in patients with depression is between 30% and 70% [5], and it has been shown to prospectively predict more severe depressive symptoms in the future [6]. Anhedonia is also associated with reduced quality of life [7] and social functioning [8, 9] in patients with mental illness and poorer response to medication in patients with depression [10]. Therefore, it is essential to understand the influencing factors of anhedonia and the underlying mechanisms, thus developing targeted interventions to manage anhedonia for patients with depression.

Negative life events are defined as unpleasant, uncontrollable, and generally stressful experiences that have a negative impact on individuals’ life [11]. It has been showed that early negative life events [12, 13] and childhood adversity [14] could lead to anhedonia. Previous studies in psychiatric populations provided further evidence that negative life events caused stress exposure could cause anhedonia [15, 16]. An animal experimental study has found that both acute and chronic stress could induce anhedonia behavior in depressed mice [17]. Although the construct validity of animal models for anhedonia and depression is still debated, animal experiments allow researchers to precisely manipulate stress exposure, environmental conditions, and developmental experiences, which cannot be ethically or practically controlled in human studies. However, despite these mechanistic insights from controlled experimental models, this hypothesis has not been systematically examined in large samples of patients with depression. In addition, the pathways through which negative life events contribute to anhedonia in clinical populations remain unclear and warrant further investigation.

Diathesis-stress model is a classic theory of the etiology of depression [18, 19]. The model suggests that stress may activate an individual’s diathesis (e.g., emotional state, emotional characteristics, and cognitive style) or vulnerabilities, which can change an individual’s underlying behavioral and psychological tendencies, thereby leading to mental illness (e.g., depression) [20]. Under the framework of this model, previous researchers have explored multiple individual diathesis factors that can contribute to depression, including cognitive level and bias [21] and temperament and character traits [22].

Findings from previous studies suggest that insomnia and dysfunctional attitude may mediate the relationship between negative life events and anhedonia. It has been showed that negative life events related stress is significantly linked to insomnia in students with depression [23]. Additionally, the severity of insomnia has been reported to negatively affect anhedonia of patients with depression [24]. According to the theory of diathesis stress, an individual’s dysfunctional attitude can also affect mental health [21]. Previous studies have reported that negative life events can lead to dysfunctional attitude [25], which is common in patients with depression [26]. Wang et al. [27] found that early negative life events in patients with depression could affect anhedonia by influencing dysfunctional attitude. Previous studies have shown that insomnia could affect dysfunctional attitude [9, 28]. According to existing literature, it can be inferred that negative life events may be linked to insomnia and dysfunctional attitudes, and insomnia may be associated with dysfunctional attitudes, and negative life events may be linked to insomnia and dysfunctional attitudes, which together may be associated with anhedonia.

Previous research has revealed a correlation between negative life events, insomnia, dysfunctional attitude and anhedonia. However, few studies have comprehensively explored the relationships of negative life events, insomnia, dysfunctional attitude, and anhedonia, especially in the depression population. A chain mediation model refers to a theoretically ordered sequence in which an independent variable is associated with a dependent variable through multiple intervening variables [29]. This model allows researchers to examine not only the direct association between an independent variable and a dependent variable, but also the specific pathways through which multiple mediators may operate sequentially within the proposed framework. It provides a conceptual structure for understanding the ordering of psychological processes and can identify mechanisms that may be overlooked by simpler parallel mediation models. Using a chain mediation model may also help identify potential intervention targets at different stages within the hypothesized pathway, offering a more precise and nuanced understanding of complex psychological relationships [29]. The current study aims to construct structural equations to examine whether negative life events are associated with anhedonia through insomnia and dysfunctional attitudes in patients with MDD. As shown in Fig. 1, the following hypotheses are proposed: (1) negative life events are directly associated with anhedonia; and (2) insomnia and dysfunctional attitude play a chain mediating role between negative life events and anhedonia.

Based on the diathesis-stress model of depression, this study constructed a hypothesis model suggesting that negative life events are associated with anhedonia via insomnia and dysfunctional attitudes. The results showed that negative life events were directly associated with anhedonia, insomnia and dysfunctional attitudes statistically mediated the association between negative life events and anhedonia. This establishes the foundation for delving into the underlying mechanisms through which negative life events are associated with anhedonia and offers insights into interventions aimed at ameliorating anhedonia.

This study showed that patients with MDD in the anhedonia group had more severe negative life events than patients with MDD in the non- anhedonia group, which was consistent with previous research findings [43]. Moreover, this study showed that negative life events were directly associated with anhedonia in patients with MDD, which was consistent with the results of studies in patients with schizophrenia [44]. In stressful situations resulting from negative life events, patients with depression may perceive neutral or ambiguous environmental cues as threatening or negative stimuli, which may be associated with increased anhedonia [45]. This study also revealed that patients with MDD in the anhedonia group experienced more severe insomnia and dysfunctional attitude compared to those in the non-anhedonia group. Moreover, this study demonstrated that insomnia was directly associated with anhedonia in patients with MDD. In line with our finding, longitudinal analyses have shown that stress has been associated with sleep disturbances and insomnia, which could increase the vulnerability of individuals to depression and further affected the occurrence of anhedonia [46]. Previous study of patients with depression showed that dysfunctional attitudes directly affect anhedonia, which was consistent with our research [27]. The possible reason is that dysfunctional attitude can increase individuals’ information processing errors, which may lead to the incidence of anhedonia [26].

This study showed that insomnia and dysfunctional attitude played a chain mediating role between negative life events and anhedonia. The possible reason is that insomnia in the context of negative life events may be associated with impairments of individual attention, memory, executive ability, emotional control, fluency, psychomotor speed and other cognitive areas [9], which further affects individual information processing errors, which may be related to increased anhedonia [26]. There were few studies that explored the pathway by insomnia and dysfunctional attitude underlying negative life events and anhedonia. However, some psychological intervention studies have been shown to improve an individual’s stress, insomnia, dysfunctional attitude and anhedonia [5, 47]. For example, cognitive behavioral therapy for insomnia has been shown to relieve insomnia, dysfunctional attitude, and positive emotion [48].

The possible reason might be that the HPA axis plays a key role in stress, sleep, dysfunctional attitude and emotional regulation [49]. The activity of the HPA axis is usually associated with stress response, and the release of cortisol can affect the biological clock and sleep pattern [50]. High levels of cortisol are also associated with decreased cognitive function [50]. This in turn affects structural and functional changes in brain regions such as the hippocampus and prefrontal cortex, which are closely associated with cognitive function. Poor sleep quality is closely linked to decreased cognitive function, including learning, memory, and concentration, resulting from insufficient deep sleep [51]. Thus, the HPA axis affects sleep by regulating cortisol levels, and further affects cognitive function through mechanisms related to sleep quality, and finally affects an individual’s ability to regulate emotion. Another possible explanation is that negative life events may impact the reward system [52], possibly due to stress-induced activation of the stress response system, altering dopamine and serotonin levels [52]. Reward system damage may disrupt sleep regulation, leading to insomnia [53, 54]. Insomnia worsen emotional and cognitive decline affecting responsiveness to rewarding stimuli, which in turn affects anhedonia [26]. Hence, these two potential mechanisms may help explain the observed association between negative life events and anhedonia at neurological and physiological levels.

To the best of our knowledge, this is the first study to comprehensively review the pathways linking negative life events, insomnia, dysfunctional attitudes, and anhedonia among patients with MDD. Our findings suggest that negative life events were associated with anhedonia both directly and indirectly via insomnia and dysfunctional attitudes. Healthcare professionals should therefore assess insomnia and dysfunctional attitudes in patients with MDD and provide targeted interventions when necessary (e.g., Lee et al. [55], Eigl et al. [56], Leerssen et al. [48]). For patients with MDD, health education programs should focus on the identification of anhedonia. Patients should be taught to recognize when they experience a diminished interest or pleasure in daily activities. In addition, interventions should emphasize the cultivation of positive experiences to counteract anhedonia. This study also highlighted the importance of monitoring and addressing negative life events in patients with MDD [57]. Healthcare professionals should provide patients with practical strategies to cope with stress and adverse experiences. Furthermore, it is essential to educate patients about insomnia and implement structured programs to improve sleep quality [58]. Improving sleep may reduce the cognitive and emotional consequences associated with MDD. Cognitive factors should also be addressed in clinical care [59]. Dysfunctional attitudes and cognitive biases can contribute to the development and maintenance of anhedonia, and patients should be supported in identifying and modifying these cognitive patterns. By combining these approaches, healthcare professionals can provide more comprehensive care and better support patients in managing anhedonia. Finally, future research should adopt more rigorous designs to further explore the causal relationship of insomnia and dysfunctional attitudes in the impact of negative life events and anhedonia among patients with depression. Tailored interventions targeting negative life events, insomnia, and dysfunctional attitudes may help develop more effective treatment strategies for patients with MDD and improve overall mental health outcomes.

The current study has some limitations. Firstly, cross-sectional data were used in this study, limiting causal inference between variables. Future studies can design longitudinal follow-ups to further explore the research hypotheses in this study. Secondly, this study employed the method of self-assessment questionnaires, which may lead to reporting bias when patients fill in the questionnaire. Future research can evaluate variables using objective indicators, e.g., measuring stress levels using cortisol levels. Third, the structural equation model specified in this study was a saturated model, which precluded empirical evaluation of global model fit indices. Consequently, the adequacy of the proposed model structure could not be statistically compared with alternative theoretically plausible models. Although the path coefficients were statistically significant, the saturated nature of the model limits the strength of structural inference and warrants cautious interpretation of the sequential mediation pathways. Future research should test competing models to provide stronger evidence for the proposed structure. Fourth, stress resulting from negative life events can be specifically categorized into acute and chronic stress; however, this study only measured chronic stress using the LES questionnaire, and not measured acute stress of the participants. Future studies are suggested to facilitate a more comprehensive investigation of how these two types of stress affect anhedonia. Fifth, detailed data on participants’ current or recent use of psychotropic medications were not collected in this study. The use of such medications may have a confounding effect, as many psychotropic agents can influence both anhedonia levels and insomnia severity. This limitation should be considered when interpreting the results. Future research should collect detailed information on medication types, doses, and duration to better control for potential confounding effects. Finally, the generalizability of the findings may be limited by the demographic characteristics of the sample. The majority of participants were female and relatively young, which may not fully represent the broader population of patients with major depressive disorder. Replication in more gender-balanced and age-diverse samples is necessary to enhance external validity.

This study found that negative life events were associated with anhedonia among patients with MDD and insomnia and dysfunctional attitudes statistically accounted for the association between negative life events and anhedonia in a sequential mediation model. For patients with MDD with negative life events, addressing sleep problems and dysfunctional attitudes may be considered as potential intervention strategies for patients experiencing anhedonia.