Relationship problems can keep us awake at night. But new research from UC Berkeley suggests that sleepless nights also can worsen lovers’ fights.

UC Berkeley psychologists Amie Gordon and Serena Chen have found that people are much more likely to lash out at their romantic partners over relationship conflicts after a bad night’s sleep.

“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 the journal, 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,” she added.

While previous studies indicate that poor sleep has a negative impact on romantic relationships, these new findings shed more light on how bad sleep compromises couples’ ability to avoid and manage conflict, researchers said.

“For the first time, to our knowledge, we can see the process of how the nature, degree, and resolution of conflict are negatively impacted by poor sleep,” said Chen, a professor of psychology at UC Berkeley.

Researchers collected data on the sleep habits of more than 100 couples who had been together, on average, for nearly two years. They gauged 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 two-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,” Chen said.

In a second experiment, 71 couples came into the laboratory, rated how they had slept the previous night, and then, while being videotaped, discussed with their partners a source of conflict in their relationship. Each partner then rated his or her own and his or her partner’s emotional interactions during the conflict conversation, and assessed whether they resolved the disagreement.

The participants who had slept poorly and their partners reported feeling more negatively toward one another during the conflict discussion, according to observations and their reports. Their conflict-resolution skills and ability to accurately gauge their partners’ emotions also suffered after a bad night’s sleep.