Introduction
Major depressive disorder (MDD) is a prevalent mental disorder that imposes a heavy burden on patients. According to the criteria in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5), insomnia symptoms are a notable feature of MDD, affecting up to 90% of patients [
1,
2]. In patients with MDD, insomnia is associated with greater severity of depression, increased risk of recurrence, worse response to antidepressant treatment, more severe functional deficits, and worse quality of life [
3‐
5]. Thus, the identification of risk and protective factors for insomnia may have novel implications for the prevention and treatment of patients with MDD.
Personality traits have been hypothesized to predispose patients to insomnia and are potentially perpetuating factors for insomnia [
6]; among these, higher neuroticism is the most consistently associated with insomnia [
7,
8]. Lower extraversion is also associated with insomnia, but the results have been inconsistent [
7,
8]. Although the relationship among personality, insomnia, and depression has been frequently investigated, the results regarding their interactions have been inconsistent. Neuroticism may mediate the relationship between sleep disturbances and depression [
9], while subjective sleep quality or depressive symptoms mediate the association between the other two variables [
10]. In addition, current research on the impact of personality traits on specific insomnia symptoms in patients with depression is limited. Conducting relevant research may be crucial for individualized treatment of MDD patients with insomnia symptoms.
Adverse childhood experiences (ACEs) are another risk factor for depression and insomnia. A meta-analysis suggested that experiencing childhood maltreatment may lead to recurrent, chronic, and treatment-resistant depression [
11]. Childhood trauma is a risk factor for poor sleep health in adulthood, even after controlling for depression history and current stress [
12]. Furthermore, insomnia may be a key mechanism by which individuals with a history of trauma are rendered vulnerable to depressive episodes [
13]. Identifying the specific types of trauma associated with insomnia and depression is critical to the individualized treatment of these patients, but the relevant research findings are inconsistent [
14].
Interpersonal disturbances are associated with both insomnia and depression [
15,
16]. Compared to controls, individuals with insomnia reported a higher level of interpersonal distress [
16] and more cognitive-interpersonal problems (e.g., insecure attachments), which are associated with hyperarousal traits, presleep hyperarousal, and emotion dysregulation [
17]. Interpersonal psychotherapy for insomnia significantly improved postsleep arousal, sleep efficiency, and total sleep time in patients with primary insomnia [
18]. Therefore, more detailed identification of the types of interpersonal distress associated with insomnia can provide insights for targeted interventions to address both interpersonal distress and insomnia.
Among multiple psychosocial factors, social support appears to be a protective factor against insomnia and depression [
19,
20]. Good social support is associated with shorter self-reported sleep latency and reduced actigraphy-assessed postsleep wakefulness [
19]. Family, peer and school support has been suggested to promote healthy sleep behaviors [
21]. In addition, childhood trauma, neuroticism, interpersonal distress, and social support are interrelated, and their interactions affect insomnia and depression. For example, supportive interpersonal relationships may help mitigate the effects of adversity and promote adaptive functioning in youth [
22]. The protective effect of social support on depression has been demonstrated in risky situations associated with early-life stress [
23]. Neuroticism plays a mediating role between childhood adversity and poor sleep quality [
24]. Nonetheless, few studies have evaluated the combined effect of these psychosocial factors or identified which factors are the most influential and directly influence insomnia and depression. Network analysis, which views mental disorders as the result of a dynamic interaction of symptoms, has recently been used to explore the independent associations between all pairs of variables included [
25]. In the visualization framework obtained from network analysis, symptoms or valuables are represented as nodes, and their conditional dependence relationships are represented as edges [
26]. Network analysis can identify central symptoms [
25] as well as bridge symptoms that connect diseases or psychological domains [
27], ultimately helping to identify potential targets for prevention and treatment of mental disease [
25].
The present study aimed to broaden the previous research based on individual risk factors or sum scores of insomnia symptoms by conducting multifactorial network analyses of individual insomnia symptoms in patients with MDD; this was achieved by (1) constructing an insomnia network to identify the most central symptoms of insomnia; (2) constructing four separate networks of individual insomnia symptoms with personality traits, childhood trauma, interpersonal disturbances, or social support to identify and screen for insomnia-associated psychosocial factors to include in the final multifactorial networks; and (3) constructing a multifactorial model of individual insomnia symptoms and psychosocial factors selected from the previous step to identify the bridge nodes and shortest pathways from psychosocial factors to insomnia symptoms.
Discussion
To expand the current understanding of individual risk factors for sum-scores-based insomnia, we used network analysis to investigate the relationships of insomnia symptoms and social support, interpersonal disturbance, personality traits, and childhood trauma in patients with MDD for the first time. First, worrying about sleep was the most stable central symptom of insomnia symptoms. Second, social support, interpersonal disturbance, and personality traits were selected for inclusion in the final multifactorial networks, while childhood trauma was excluded because variables in this domain did not relate to insomnia. Third, neuroticism was the bridge node and was directly related to the total ISI score in the integrated network of the total ISI score and associated psychosocial factors, as well as insomnia symptoms, especially worrying about sleep, in the integrated network of insomnia symptoms and associated psychosocial factors. Other psychosocial factors were indirectly linked to insomnia symptoms through neuroticism, as observed when considering the shortest pathways. Finally, after adjusting for depression severity and pharmacological treatments, worrying about sleep remained the most central insomnia symptom. Although weakened, the significant associations between neuroticism and insomnia symptoms persisted after adjustment, indicating that these associations were stable; thus, the main conclusions of this study did not change after considering covariates.
The major finding of this study was that worrying about sleep has a high centrality value among insomnia symptoms, consistent with previous studies [
39]. Worrying about sleep fundamentally reflects dysfunctional beliefs about sleep from the cognitive perspective rather than the severity of sleep disturbances. The crucial role of cognitive factors in the development and maintenance of insomnia has been supported by cognitive models of insomnia, which implies that long-term concern and reflection on sleep-related problems may contribute to converting acute insomnia into chronic insomnia [
40]. Currently, cognitive behavioral therapy for insomnia (CBT-I) has been shown to improve insomnia, but its mechanism remains unclear [
41]. In the present study, worrying about sleep was most strongly associated with dissatisfaction with sleep and multiple daytime complaints of insomnia, such as interference with daily functioning and how noticeably sleep problems impair quality of life; thus, worrying about sleep may be an important target for CBT-I, which includes treating a patient’s expectations and beliefs about sleep and daytime complaints [
42,
43].
Another interesting finding is the bridging effect of neuroticism. We found that insomnia severity was most strongly and directly associated with neuroticism but not with extraversion, consistent with a network analysis of insomnia and five-factor personality traits in the general population [
44]. This can be explained by a previous study that found a tendency toward neuroticism in self-reported insomniacs and a tendency toward introversion in objectively measured insomniacs [
45]. Our findings support the idea that neuroticism is a stable predictor of insomnia. A study investigating the effects of anxiety sensitivity, dysfunctional beliefs about sleep, and neuroticism on sleep disturbance found that neuroticism was the most statistically important predictor, potentially because neuroticism is implicated in internalizing negative emotions and enhancing emotional and physiological arousal, which directly affect sleep [
46]. Furthermore, neuroticism may activate metacognitive beliefs of insufficiency, further exacerbating sleep problems [
47]. Assessing neuroticism may not only facilitate the early identification of insomnia-prone individuals but also facilitate individualized intervention measures because insomniacs with neurotic characteristics could benefit from behavioral treatment [
48]. In addition, neuroticism may be a potential target for future treatment, as interventions that alter a person’s overall tendency to experience negative emotions (or conversely, to succeed in increasing positive emotions) may lead to an improvement in insomnia symptoms. Perhaps CBT-I treatments could be expanded to include elements that target neuroticism. Although neuroticism is considered a stable personality trait in adulthood, changes in neuroticism levels during antidepressant treatment have been found to correlate with improved outcomes [
49]. On the other hand, our findings that neuroticism was directly connected with worrying about sleep differ from those of a previous study demonstrating that neuroticism relates to interference with daily functioning and difficulty initiating sleep [
44]. This could be due to differences in populations and the assessment methods used to evaluate neuroticism. Previous studies were conducted in the general population and administered a five-factor personality test, while this study was conducted in MDD patients and used the EPQ. Therefore, it is necessary to use network analysis to study the mechanism of insomnia in different populations.
This study found that certain nodes from interpersonal problems and social support were associated with insomnia, such as the relationships of the manner of dealing with people–interference with daily functioning and objective support–difficulty initiating sleep, in the network of insomnia symptoms and individual psychosocial factors as well as in the network of the total ISI score and integrated psychosocial factors. However, their connections were weak and disappeared after adjusting for covariates, and nodes from interpersonal problems and social support were indirectly related to insomnia symptoms through neuroticism in the final network of individual insomnia symptoms and integrated psychosocial factors. One explanation is that interpersonal disturbances and poor social support induce psychological stress; as individuals with neuroticism are sensitive to stress, the increased perceived stress and corresponding response may further lead to insomnia [
50]. Another interesting finding of this study is that although neuroticism, psychoticism, and extraversion were not directly linked, all three personality traits were associated with interpersonal distress. For example, neuroticism is positively associated with difficulty in dealing with people and making friends; psychoticism is positively correlated with disturbances in dealing with people and conversation; and extraversion is negatively correlated with disturbances in conversation and making friends. These results are supported by previous research, which suggests that extraverts have better social skills, experience less social anxiety and are chosen as friends more often than introverts, while individuals with high neuroticism tend to lack social skills and experience social anxiety [
51]. In addition, extraversion is positively correlated with subjective social support and support utilization, mainly because extraverts tend to form more embedded and durable connections in friendship networks than introverts [
52]. Thus, the impacts of interpersonal distress and poor social support on insomnia may be mitigated by ameliorating personality abnormalities and their consequent adverse psychological consequences.
The present study is the first to explore the association between childhood trauma and insomnia using network analysis but found that there was no association, which is inconsistent with the finding of most previous studies that childhood traumas are associated with sleep health in adulthood [
12]. The discrepancy may be due to the different methods of analysis. Our study is supported by a previous study that found that childhood stress was not associated with subjective sleep quality but was associated with objective sleep quality [
53]. Future research should focus on adverse childhood experiences and insomnia measured using objective methods, such as wrist actigraphy.
Strength
This study is the first to use network analysis to explore the relationship between insomnia and multiple psychosocial factors in patients with depression. It expands on previous studies that used individual factors or sum scores to determine the independent effects of psychosocial factors. This study has several clinical implications. First, worrying about sleep may be an important target for insomnia treatment due to its central position. Second, neuroticism may facilitate the early identification of insomnia symptoms and the selection of the most appropriate treatment, such as behavioral therapy; CBT-I interventions can target neuroticism. Finally, in patients with interpersonal problems or poor social support, neuroticism can be measured to guide treatment, as it acts as a bridging valuable.
Limitations
This study still has several limitations to note. First, over half of the sample consisted of females with an undergraduate or higher education level, making it difficult to generalize the results to males and those with a high school or lower educational level. Second, we used self-assessment questionnaires to assess insomnia, which may be biased compared to the results of objective assessment methods. Future studies can further use objective assessments, such as electroencephalography, to supplement the current findings. Finally, the study population was relatively young; therefore, a larger sample size and more participants in other age groups are needed to validate the results.
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