According to a new study, happy couples snooze in sync.

Couple sleeping
Credit: Troels Graugaard/Getty Images

One way that happy couples are alike? Synchronized alarm clocks—and bedtimes. A study published this month in the journal Sleep revealed that how couples sleep together is influenced by how satisfied they are with their marriage. The 46 participating couples reported that those who shared a bed were simultaneously awake or asleep in it about 75 percent of the time. When wives felt higher satisfaction in their marriages, that number rose, as they synced their sleep patterns even more closely with their husbands’.

But shared sleep habits apparently not only expose truths about relationships, they can also affect them. Some more findings:

  • Forget what you see in the movies: The majority of the couples surveyed for a study published in April by the University of Hertfordshire in the U.K. slept back-to-back rather than in the same direction (or face-to-face). Regardless of their positions, though, according to the same study, couples who sleep an inch apart tend to be happier than those who sleep 30 inches apart: Ninety-four percent of couples who fall asleep while touching their partner reported a happy relationship; only 68 percent of those who didn’t touch reported the same satisfaction.
  • A poor night’s sleep can mean more than under-eye circles: It can be a precursor to relationship conflict, concluded a study published by the University of California—Berkeley in July 2013 in the journal Social Psychological and Personality Science. Couples are more likely to fight the day after a restless night. Sleep deprivation can also lead to a reduced ability to read a partner’s emotions and an increase in negative feelings, worsening arguments.
  • Losing sleep can also affect a sense of gratitude toward partners, another UC Berkeley study said, this one from January 2013. Couples who spent the night agitated or distracted instead of snoozing serenely are less likely to feel appreciation for their relationship or demonstrate appreciation the next day.
  • Married women may be more susceptible to the damaging relationship effects of insufficient shut-eye than their husbands, said a 2011 study funded by the National Institutes of Health. Wives who don’t have peaceful nights are more likely to initiate negative interactions with their husbands in the morning. Men aren’t as likely to be triggered in the same way.