Poor sleep can bring out the ‘dark side’ of personality at work, study finds

New research highlights a link between how well employees sleep and the expression of darker personality traits in the workplace. The study, published in the Journal of Organizational Behavior, found that on days when workers reported poorer sleep, they were more likely to show higher levels of narcissism, Machiavellianism, and psychopathy. These effects were partly explained by their ability—or inability—to tolerate distress, pointing to sleep as an overlooked factor influencing toxic behavior at work.

The so-called “dark triad” of personality—narcissism, psychopathy, and Machiavellianism—has long been associated with counterproductive behaviors and harmful dynamics in the workplace. However, most research has treated these traits as stable and enduring characteristics. The current study instead focused on short-term fluctuations—what the researchers call “dark triad states”—and explored how everyday factors like sleep quality and quantity might influence these temporary expressions of darker tendencies.

“This interest originated from the realization that we all possess dark personality traits to some extent, with individuals in powerful organizational roles often scoring particularly high on these dark traits,” said study author Evy Kuijpers, a postdoctoral researcher at Vrije Universiteit Brussel.

“While identifying these characteristics is important, it’s just as crucial to understand that they’re not fixed and can fluctuate in everyday work life. Recognizing that certain factors can trigger these dark expressions led us to explore why and when they occur, with the hope that this understanding could eventually help prevent them from developing into more persistent patterns of behavior.”

The researchers conducted a 10-day experience sampling study with 103 working adults from Belgium and Argentina. Participants were asked to complete two surveys each day—one in the morning and one in the late afternoon. In the morning survey, participants rated the quality and duration of their sleep the night before. In the afternoon, they reported how they felt throughout the day, including their levels of narcissism, Machiavellianism, psychopathy, and distress tolerance.

To measure dark triad states, the researchers used an adapted version of the “Dirty Dozen” scale, which includes brief descriptions of dark personality traits framed as daily self-perceptions (e.g., “Today, I used deceit or lied to get my way”). They also included a single-item measure of distress tolerance, which reflects the extent to which individuals felt capable of handling emotional discomfort that day.

Overall, the researchers collected 786 complete daily records from the participants. Their analysis revealed that both sleep quality and quantity were negatively related to daily expressions of the dark triad. In other words, when individuals reported sleeping poorly or getting fewer hours of rest than usual, they were more likely to express manipulative, self-centered, or emotionally detached behaviors at work.

Each of the dark triad components—narcissism, Machiavellianism, and psychopathy—was significantly affected by sleep. For instance, poorer sleep predicted higher levels of psychopathy (such as a lack of remorse) and Machiavellianism (like using others for personal gain), as well as narcissism (desiring admiration). These associations remained significant even after controlling for individual differences, indicating that it wasn’t just that some people are more prone to these traits than others, but that individuals tended to show more of these traits on days when they had worse sleep.

“We were somewhat surprised by how consistently sleep perception—especially sleep quality—predicted changes in dark triad states across individuals,” Kuijpers told PsyPost. “It’s also notable that even small day-to-day variations in sleep can meaningfully influence behavior.”

The researchers also tested whether the relationship between sleep and dark triad states was mediated by distress tolerance—the ability to withstand emotional discomfort. As predicted, the researchers found that poor sleep undermined participants’ distress tolerance, which in turn made them more likely to exhibit dark triad behaviors. For example, after a night of poor sleep, individuals reported feeling less able to cope with stress and frustration, which then increased the likelihood that they would act in manipulative or antisocial ways during the day.

This mediation effect was statistically significant for both sleep quality and sleep duration. However, sleep quality had a somewhat stronger effect, suggesting that how restful someone’s sleep feels may be more important for self-regulation than the exact number of hours they slept.

To explore whether these relationships might go in both directions, the researchers also tested whether expressing dark traits during the day affected sleep the following night. There was some evidence of reverse effects, particularly for Machiavellianism, which was unexpectedly associated with better sleep. However, these effects were small, and the amount of variation in sleep explained by dark triad states was minimal—less than 2%—suggesting that sleep is more likely to influence dark personality states than the other way around.

“This study looked at how sleep affects people’s tendency to show darker behaviors at work, like being manipulative or self-centered,” Kuijpers said. “We found that when people sleep poorly — both in quality and quantity — they’re more likely to act this way, partly because they struggle more with handling stress. These findings highlight the importance of good sleep for helping employees manage their emotions and avoid harmful behavior at work.”

The authors argue that these findings have important practical implications. Because dark triad behaviors can damage workplace relationships, reduce job performance, and contribute to a toxic environment, understanding their triggers can help employers develop strategies to reduce their occurrence. Given that sleep is both modifiable and strongly tied to workplace functioning, organizations might consider promoting healthy sleep habits among employees as a way to foster a more positive work culture.

For example, limiting long working hours, encouraging breaks, offering flexible schedules, and providing education about sleep hygiene could all contribute to better sleep quality. Some companies may even consider designated rest spaces or nap policies to help employees recharge during the day—especially if doing so helps reduce harmful behaviors and improves team dynamics.

The study also contributes to a growing body of research calling for a more dynamic view of personality. Rather than assuming that dark personality traits are fixed and unchangeable, the findings suggest that situational factors like sleep can play a significant role in shaping how these traits are expressed on a day-to-day basis. Over time, repeated patterns of poor sleep and low distress tolerance could potentially lead to more stable personality changes, highlighting the importance of early intervention.

But the authors acknowledge some limitations. While they measured sleep and dark triad states at different times of day, the mediator—distress tolerance—was assessed at the same time as the outcome variable, which limits the ability to draw firm conclusions about causality. All measures were self-reported, which may introduce bias. The study also relied on a relatively simple daily measure of dark traits, and future research may benefit from more detailed or behavior-based assessments.

“While our study shows a link between sleep and dark behaviors at work, it relies on people’s own reports (i.e., subjective assessment of sleep) which may not always be reflective of their actual sleep quality/quantity,” Kuijpers noted. “Using more precise sleep tracking devices may help confirm and expand these findings.”

“Our long-term goal is to deepen our understanding of the factors that trigger dark personality states at work, given that these traits can cause significant harm to both individuals and organizations. Specifically, we aim to identify additional situational and physiological triggers of dark triad states in order to develop targeted strategies that can mitigate their negative effects. Ultimately, we strive to foster healthier work environments where employees are better equipped to manage and control their darker impulses.”

The study, “Rise of the Dark Side: How Sleep Perception Triggers Dark Triad States at Work,” was authored by Evy Kuijpers, Jasmine Vergauwe, Sam Vanderperre, Olivier Mairesse, and Joeri Hofmans.