It started as a simple conversation about a child’s birthday party. But it quickly escalated into a full-blown marital rift. She accused him of neglecting the family. He said she was yelling.

“Whatever,” she said. “Go. Go.”

“Go where?” he replied.

“I don’t know,” she told him. “I don’t want to talk to you anymore.”

The bickering parents were among 43 couples taking part in an Ohio State University study exploring how marital interactions influence a person’s health. Every couple in the study — just like couples in the real world — had experienced some form of routine marital conflict. Hot-button topics included managing money, spending time together as a family or an in-law intruding on the relationship.

But while marital spats were universal among the couples, how they handled them was not. Some couples argued constructively and even with kindness, while others — like the couple fighting about the birthday party — were hostile and negative.

What made the difference? The hostile couples were most likely to be those who weren’t getting much sleep.

“When people have slept less, it’s a little like looking at the world through dark glasses,” said Janice Kiecolt-Glaser, a longtime relationship scientist and director of the Ohio State Institute for Behavioral Medicine Research. “Their moods are poorer. We’re grumpier. Lack of sleep hurts the relationship.”

The men and women in the study had been married from three to 27 years. They reported varying amounts of sleep — anywhere from three and a half to nine hours a night. Each couple made two visits to the lab, where the partners were prodded to talk about the issues that caused the most conflict in their relationship. Then the researchers analyzed videos of their exchanges using well-established scoring techniques to assess positive and negative interactions and hostile and constructive responses. After all the data were parsed, a clear pattern emerged.

Couples were more likely to be hostile — like the couple fighting about the child’s birthday party — when both partners were functioning on less than seven hours of sleep.

Notably, the couples with more than seven hours of sleep still argued with each other, but the tone of their conflict was different. Consider this couple discussing concerns about spending and budget challenges.

“Do you want to try taking over the budget?”

“I can’t. I don’t want to.”

“I understand.”

“You’re just being too accepting. You can tell me I’m crazy.”

“You’re not crazy.”

Although the couple had indicated they regularly argued about money issues, getting adequate sleep seemed to give them the patience to approach conflict in a constructive way.

“It’s not the fact that the couples were disagreeing,” Dr. Kiecolt-Glaser said. “It’s the lack of sleep and the way in which they disagreed.”

She continued: “The better functioning couples could do it with humor and kindness but clearly still disagree. The poorer functioning couples could get pretty nasty.”

The notion that better sleep makes a better marriage isn’t entirely new. A large body of research suggests that sleep-deprived people are more unpleasant and even hostile in their social interactions than those who get adequate sleep. People tend to use more negative words when they are sleep deprived than on days when they have had a full night’s sleep. A 2010 study found that men were more likely to fight with their wives after a night of disturbed sleep. In a 2014 study, couples who reported poor sleep during a two-week period reported more daily marital conflict than those who got better sleep.

But the Ohio State study went a step further to measure how marital discord combined with sleep deprivation can become toxic to a person’s health. Each partner in the study also gave blood samples, before and after the fight with their spouse. The samples were to measure markers of inflammation, which has been linked with heart disease, cancer and other health problems.

The study found that when married partners got less sleep, not only were they more likely to have hostile conflicts, but they also had higher levels of inflammatory proteins in their blood after those conflicts. In short, marital discord is more toxic to your body when you haven’t gotten enough sleep.

“Lack of sleep not only hurts the relationship,” said Dr. Kiecolt-Glaser, the senior author on the study, which was published in May in the journal Psychoneuroendocrinology. “It makes relationship conflict harder on the body.”

There was some good news from the study. When one partner got more rest, it was possible to mitigate the impact of sleep deprivation on the other partner. Couples with one rested partner were less likely to engage in hostile exchanges than when both partners were sleep deprived.

“Sleep and conflict worked together to increase inflammation, but both partners’ sleep mattered,” said Stephanie Wilson, the study’s lead author and a postdoctoral fellow at Ohio State. “When one person was rested, it protected the couple from being more nasty to each other.”

Sleep problems in a relationship aren’t uncommon. The National Sleep Foundation found that nearly 25 percent of couples sleep in separate beds. Other research shows that having a bed partner affects how much and how well a person sleeps. And when one relationship partner doesn’t sleep well, his or her partner is more likely to report poor health and well-being.

While the recent study examined only heterosexual married couples, the findings likely are relevant to all couples, including cohabiting couples and gay and lesbian partners. “These are universal relationship processes,” said Dr. Wilson. “Just knowing these effects can happen can help people keep in mind the importance of getting a good night’s sleep and treading carefully with conflict.”

The lesson, say the study authors, is that before concluding a relationship is in trouble, couples who regularly experience conflict should take stock not only of the relationship and how they are managing conflict, but also of their sleep habits.

“Losing sleep here and there and coming across interpersonal tensions in daily life is really common for people,” Dr. Wilson said. “These are small vulnerabilities that may add up. It teaches you the importance of getting rested every night and handling disagreements in a mindful way.”