For the study, presented today at Sleep 2011, the 25th anniversary meeting of the Associated Professional Sleep Societies in Minneapolis, 35 healthy, married couples wore actigraphs -- bracelets that measured the time it took each partner to fall asleep after going to bed and the total time each slept over 10 days. The couples also kept a diary in which they recorded positive and negative interactions with their spouse.
The study found that wives' sleep difficulties affected their own and their spouses' marital interactions the following day.
"Wives who took longer to fall asleep the night before reported poorer interactions with their husbands the next day," said Wendy Troxel, assistant professor of psychiatry and psychology at the University of Pittsburgh and lead author of the study. And their husbands reported poorer interactions with their wives.
Several studies have linked sleep deprivation to irritability. And "when you're irritated, the person you're most likely to take it out on is your spouse," Troxel said.
"For sure when someone is sleep deprived they become more emotionally brittle," said Susan Heitler, a Denver marriage counselor and co-founder of poweroftwomarriage.com. "A situation that might have been humorous or just slightly frustrating looks downright annoying. It's like putting on dark glasses, to not have enough sleep."
But, said Troxel, "it's equally possible that how you interact with your spouse during the day could affect sleep at night."
Emotions could cause women to toss and turn in bed as they worry about work, marriage and motherhood, said Heitler. "That kind of lying in bed with an overloaded mind may be characteristic of women in society right now, particularly women with children and a full-time job."
The study, which is still in progress, so far suggests that sleep disturbance affects marital interactions and not vice versa. Surprisingly, when husbands got less sleep, it had the opposite effect. It boosted their marital bliss -- an effect that might reflect what went on after the lights went out.
"The actigraphs only measure the time it takes for someone to fall asleep after they went to bed," said Troxel, adding that the couples were instructed to start the timer when they turned out the lights. "When a husband is sleeping less, it may be because he's engaged in other pleasurable interactions."
Troxel couldn't say with certainty whether sex played a role in men's positive outlook on marriage after a shorter night's sleep because the study is still under way. But she hopes the couples' diaries will shed light on the topic, which has not been well-studied.
"There's very little known about sexual activity and sleep," Troxel said. "It's a hard topic to investigate and very hard to get funding for."
Troxel plans to recruit 12 more couples before completing her final analysis, which she hopes will start to uncover how sleep influences relationships and health.
"There's a great deal of research focused on the impact of social relationships on health, and a great deal focused on marital quality and cardiovascular health," she said. "It appears that being married is good, but it has to be a high-quality marriage."
And sleep, the study suggests, could be an important determinant of marriage quality.
"Sleep is a critical health behavior that happens to be one that couples engage in together," Troxel said. "Understanding the dynamic link between relationships and sleep might help us to understand how relationships get under the skin to influence health and wellbeing."