New research out of the University of California, Berkeley suggests that lack of sleep can contribute to relationship conflicts. Psychologists Amie Gordon and Serena Chen have discovered that people who have had a sleepless night are much more likely to lash out at their romantic partners over relationship tensions.

Previous studies have shown that poor sleep has a negative impact on romantic relationships, but the findings from this study shed light on how severely lack of sleep compromises couples’ ability to avoid and manage conflict.

“Couples who fight more are less happy and less healthy,” said Gordon, a doctoral student in psychology and lead author of the study published online in Social Psychological and Personality Science. “Our research helps illuminate one factor that leads couples to engage in unnecessary and harmful conflict by showing that couples experience more frequent and severe conflicts after sleepless nights.”

Researchers collected data on the sleep habits of more than 100 couples who had been together, on average, for nearly two years. They assessed participants for depression, anxiety, and other stressors in order to focus solely on the link between the couples’ sleep quality and relationship conflicts.

In one experiment, 78 young adults in romantic relationships provided daily reports over a 2-week period about their sleep quality and relationship stresses. Overall, participants reported more discord with their partners on the days following a bad night’s sleep.

“Even among relatively good sleepers, a poor night of sleep was associated with more conflict with their romantic partner the next day,” said Chen.

In a second experiment, 71 couples rated how they had slept the previous night, and were then filmed discussing a source of conflict in their relationship. Each partner then rated their personal emotional interactions during the conflict conversation, as well as their partner’s emotional interactions. They then assessed whether they resolved the disagreement.

The participants who had slept poorly reported feeling more negatively toward one another during the conflict discussion, according to observations and their reports.

Findings concluded that participants’ conflict-resolution skills and ability to accurately gauge their partners’ emotions suffered after a bad night’s sleep.