Affective disorders (AD) subsume psychiatric diseases, which share the symptom of mood dysregulations. For example, depression encompasses depressed mood and/or loss of pleasure or interest. Bipolar disorder includes both depressive and manic episodes, the latter subsuming euphoria and/or heightened irritability. Both share the symptom of disturbed sleep, e.g., an increased or decreased need for sleep, insomnia, or difficulties falling or remaining asleep (World Health Organization, 2022). Hence, the association between AD and sleep has been frequently investigated, revealing that disturbed sleep serves as a symptom and risk factor in AD (Fang et al., 2019). Specifically, impaired sleep continuity and decreased sleep efficiency was found in depression (e.g., Nutt et al., 2008). In bipolar disorder, which is characterized by a decreased need for sleep in manic episodes, sleep onset latency, and variability of sleep–wake patterns are impaired (e.g., Ng et al., 2015). Disturbed sleep is associated with maladaptive health behaviors, which heighten the risk of somatic and psychiatric comorbidities (Gold and Sylvia, 2016). Particularly, sleep disturbances in AD are connected to increased symptom severity, illness duration (e.g., Gruber et al., 2011), and higher suicidality (e.g., Palagini et al., 2019). Contrary, affecting sleep rhythms has been found to positively impact the trajectory of AD, which is reflected by sleep deprivation and light therapy treatments, and sleep hygiene (Walsh et al., 2014; Dallaspezia and Benedetti, 2015; Rahimi et al., 2016). Due to the role of sleep in the etiology and preservation of AD, it is necessary to understand the factors driving the relationship between sleep and AD. Previous research found that sleep disturbances and AD are associated with inflammatory processes, genetic alterations, circadian rhythm interruptions, and dys-balances in biochemical pathways (e.g., Fang et al., 2019). Moreover, social factors (i.e., lifestyle; Lopresti et al., 2013) impact sleep quality, for instance, sleep quality was found to be affected by low-intensity exercise, which also leads to better cognitive functioning (Taheri and Irandoust, 2019), overall performance and well-being (Khcharem et al., 2022), and more regulated appetite (Irandoust and Taheri, 2018). These aspects are usually impaired in individuals with AD (Dalkner et al., 2021; Platzer et al., 2021). Further, psychological variables like personality traits affect both AD and sleep quality (Huang et al., 2016).

The Dark Triad traits (DT) subsume the personality traits narcissism, Machiavellianism, and psychopathy. Narcissism is characterized by grandiosity, entitlement, and superiority, while Machiavellianism encompasses cold and manipulative behavior. Psychopathy includes impulsive behavior along with a lack of empathy and remorse. Despite their unique intra-and interpersonal correlates, all traits share the common core of a socially malevolent character (Paulhus and Williams, 2002). A growing body of literature has linked the DT to dysfunctional interactional and health-related behavior, among others, disturbed sleep habits (e.g., Jonason et al., 2015a; Malesza and Kaczmarek, 2019; Dębska et al., 2021). It was observed that the DT are related to circadian rhythm disturbances and an eveningness disposition (i.e., being most active in the evening; Jonason et al., 2013; Rahafar et al., 2022). Specifically, studies examining the relationship between narcissism and sleep either indicate no association (e.g., Sabouri et al., 2016), or a positive association between narcissism and sleep disturbances (e.g., Ellison et al., 2013). Relatedly, individuals high Machiavellianism and psychopathy reported poorer sleep quality, more sleep disturbances, and insomnia symptoms (Sabouri et al., 2016; Akram et al., 2018; Yang et al., 2019).

Next to a higher risk for sleep disturbances, the DT were associated with AD (Jonason et al., 2015b; Shih et al., 2021). This finding was reattracted to deteriorated emotion regulation strategies (Shen, 2022), but recent research indicated other possible relations between the DT and AD symptoms: Narcissism was found to be a protective factor acting against depressive symptoms, due to higher resilience against distress (e.g., Shih et al., 2021). For Machiavellianism, positive associations with depressive symptoms were found (Bianchi and Mirkovic, 2020). Psychopathy was shown to be positively correlated with depression, which was explained by the fact that externalization of negative moods can result in psychopathic behavior (Gómez-Leal et al., 2019). Contrarily, other studies observed that some psychopathic traits can serve as a protective factor in the development of depression, because they are related to lower stress-levels (e.g., Dalkner et al., 2018).

Considering the investigated links between the DT, sleep, and AD, it seems plausible that these constructs are interrelated. Augmenting knowledge on these relationships may benefit more personalized treatment of sleep disorders, which is fundamental in treating AD. Moreover, it is necessary to conduct research on personality traits, sleep, and AD, since findings within this context could help to identify personality-related aspects, which affect sleep quality. This, in turn, provides another possibility for monitoring and preventing sleep deterioration, which would otherwise worsen or elicit mood-related symptoms. The current study thus aims to extend knowledge on the interrelation between AD (as opposed to healthy controls, HC), the DT, and sleep quality, which is encompasses sleep initiation, sleep maintenance, and sleep quantity (Kline, 2013). Previous findings indicate that Machiavellianism and psychopathy have a negative effect on sleep quality, while there are mixed results for narcissism. However, due to the common core of the Dark Triad (e.g., Book et al., 2015; Bader et al., 2022), we assumed that narcissism would also deteriorate sleep quality in our study. Overall, we hypothesized that the individual manifestations of (a) narcissism, (b) Machiavellianism, and (c) psychopathy significantly negatively moderate the relationship between group (i.e., AD and HC) and sleep quality.

Descriptive statistics of are depicted in Table 1.

We performed Bonferroni-Holm corrected Pearson-and Spearman correlation analyses between the variables gender, age, and presence of AD, DT, and PSQI score (see Table 2). For narcissism, we observed that males and HC tended to demonstrate higher values. Regarding Machiavellianism, men scored significantly higher than women. Higher psychopathy values were found in individuals younger in age and males. Further, elder individuals and those with AD reported worse sleep quality.

To investigate whether the relationship between group (AD vs. HC) and PSQI score is moderated by the DT, we conducted three moderation analyses with the outcome variable PSQI score, the predictor variable group (AD vs. HC), the moderating variables narcissism, Machiavellianism, and psychopathy, and the covariates age and gender. For narcissism, no significant interaction effect between group and PSQI score was found (b = −0.20, 95% CI [−1.02; 0.57], t = −0.50, p = 0.620). Regarding Machiavellianism and psychopathy, a significant negative interaction effect in the relationship between group and PSQI score was found, regardless of age and gender (Machiavellianism: b = −0.76, 95% CI [−1.45; −0.08], t = −2.12, p < 0.05; psychopathy: b = −1.15, 95% CI [−2.01; −0.26], t = −2.59, p < 0.05). This indicates that with increasing levels of Machiavellianism and psychopathy, the difference in sleep quality between individuals with AD and HC decreases. Moderation statistics are depicted in Table 3.

To examine the significant interaction effects of group × Machiavellianism on sleep quality (PSQI), we conducted a simple slope analysis. Group had a significant positive effect on the PSQI score at low [θ_{AD → PSQI}|(Machiavellianism = −0.72) = 5.63, CI [4.87; 6.38], t = 14.65, p < 0.001], average [θ_{AD → PSQI}|(Machiavellianism = −0.05) = 5.12, CI [4.46; 5.67], t = 18.02, p < 0.001], and high manifestations of Machiavellianism [θ_{AD → PSQI}|(Machiavellianism = 0.84) = 4.44, CI [3.63; 5.25], t = 10.77, p < 0.001]. At each examined level of Machiavellianism, sleep quality was worse in individuals with AD. Figure 1 reveals that Machiavellianism seems to play a more pronounced role in sleep quality deterioration in HC than in AD.

Regarding the interaction effect of group × psychopathy on sleep quality (PSQI score), the simple slope analysis demonstrated a significant positive effect of group on the PSQI score at low [θ_{AD → PSQI}|(psychopathy = −0.62) = 5.75, CI [4.96; 6.54], t = 14.34, p < 0.001], average [θ_{AD → PSQI}|(psychopathy = −0.17) = 5.24, CI [4.66; 5.83], t = 17.62, p < 0.001], and high manifestations of psychopathy [θ_{AD → PSQI}|(psychopathy = 0.60) = 4.35, CI [3.59; 5.11], t = 11.28, p < 0.001]. Sleep quality was worse in the AD group than in the HC group at each examined level of psychopathy. Figure 2 visualizes that psychopathy seems to play a more pronounced role in sleep quality deterioration in HC than in AD.

This study investigated the moderating effect of narcissism, Machiavellianism, and psychopathy in the relationship between AD (as opposed to HC) and sleep quality. Results reveal that Machiavellianism and psychopathy, but not narcissism, are differently associated to sleep quality in individuals with AD and HC. In HC, there is a more profound deterioration in sleep quality, depending on the individual manifestation of Machiavellianism and psychopathy, compared to AD.

Our hypothesis of narcissism posing as a significant negative moderator in the relationship between group and sleep quality was not supported by our results, since narcissism did not have a significant influence on this relationship in our study. However, this corroborates previous research on the DT and sleep behavior, which indicates no association between narcissism and sleep–wake habits (Rahafar et al., 2022), chronotype (Jonason et al., 2013), sleep disturbances (Sabouri et al., 2016), and insomnia (Akram et al., 2018; Yang et al., 2019). One explanation for this finding is that the negative relationship between the DT and sleep disturbances exists due to negatively affected cognitive-emotional processes (e.g., rumination; Sabouri et al., 2016), which is also present in AD (e.g., Kovács et al., 2020). However, individuals high in narcissism are less inclined to negative rumination due to their subjective grandiosity (Yang et al., 2019). Of all the DT, narcissism has even been determined as a buffer for negative health outcomes (Jonason et al., 2015a), but might be more relevant in other health-related behaviors. Another explanation could be the lacking differentiation between narcissism subfacets in our study. For example, Jonason et al. (2013) found a positive association between an eveningness disposition and exploitative narcissism. Similarly, vulnerable narcissism was associated with poor sleep quality (Annen et al., 2017). Differentiating between narcissism subfacets could elucidate the relationship of narcissism and sleep quality.

Further, we hypothesized that both Machiavellianism and psychopathy significantly negatively moderate the relationship between group and sleep quality, which was corroborated by our results. Indeed, Machiavellianism and psychopathy were found to pose as negative moderating variables in this relationship, indicating that these traits have a negative influence on sleep quality in both AD and HC. This is consistent with previous literature, which demonstrates the deteriorating effect of the so-called “Malicious Two” traits on insomnia symptoms (Akram et al., 2018; Yang et al., 2019), sleep disturbances (Sabouri et al., 2016), sleep and wake-up time instability (Rahafar et al., 2022), and chronotypes (Jonason et al., 2013; Costa Porfírio and Corrêa Varella, 2022). Deteriorated sleep among those high in psychopathy and Machiavellianism may be a result of insufficient emotion regulation, resulting in negatively toned cognitive activity, which affects sleep quality (Sabouri et al., 2016; Akram et al., 2018). Further, Machiavellianism and psychopathy were previously connected to cortisol levels (Dane et al., 2018), and psychopathy was associated with altered cortisol awakening responses, which could affect sleep quality (Johnson et al., 2014). These findings suggest an underlying biological pathway and highlight the interaction between personality traits, physiological aspects, and behavior. At higher levels of Machiavellianism and psychopathy, there was a more profound association between these traits and deteriorated sleep quality in HC compared to AD. Moreover, the sleep quality score only slightly changed across the personality trait manifestations in AD. This indicates that the contribution of these traits to sleep quality may be insignificant in the AD group, given the generally poorer sleep quality in AD compared to HC. Possibly, there are other variables playing a more important role in the sleep quality of individuals with AD than these traits, but do not affect HC. For instance, HC are not influenced by illness-related variables (e.g., symptomatology, Gruber et al., 2011; Becker Cretu et al., 2016), or psychopharmacological medication (Barton et al., 2022), which might affect sleep quality in AD. Moreover, worse sleep quality was previously associated with deteriorated neurocognitive functioning (Russo et al., 2015), less social relationships (Kent et al., 2015), poor health behaviors (Lee et al., 2020), and more stressful life-events (Saunders et al., 2013). All of these factors are more present in individuals with AD compared to HC, thus possibly determining sleep quality in AD rather than personality traits. Future studies should look into the exact determinants of deteriorated sleep quality in both AD and HC.

Since the previously mentioned studies were conducted in samples of HC, the current study is the first to provide data on the negative influence of Machiavellianism and psychopathy on sleep quality in individuals with AD and HC. Considering these traits could result in a more personalized treatment of sleep disorders, which could lead to an amelioration of AD. Nevertheless, Machiavellianism and psychopathy also seem to profoundly influence sleep quality of mentally healthy individuals. Thus, the individual manifestation of these traits could serve the early detection and prevention of sleep deterioration in both groups.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: Open Science Frame repository (OSF.io; https://doi.org/10.17605/OSF.IO/2Y4A9).

The studies involving humans were approved by Ethics Committee of the Medical University Graz. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

ES: conceptualization, methodology, software, validation, formal analysis, investigation, data curation, writing-original draft, writing—review and editing, visualization, and project administration. ND: conceptualization, methodology, validation, investigation, resources, writing—review and editing, supervision, and project administration. DL: conceptualization, writing—review and editing, and supervision. ER: conceptualization, resources, writing—review and editing, supervision, and project administration. AB: conceptualization, methodology, validation, formal analysis, investigation, resources, writing—review and editing, supervision, and project administration. All authors contributed to the article and approved the submitted version.

The work was supported by the Open Access publication cost funding program of the Province of Styria, Austria (ABT12-174904/2023).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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