Couples may get health benefits simply from sleeping in the same bed, a burgeoning field of study is showing. In fact, some scientists believe that sleeping with a partner may be a major reason why people with close relationships tend to be in better health and live longer.

The new research runs counter to studies that show women don't sleep as well with a partner and both men and women move around more when sleeping together. Other bed battles that interrupt couples' sleep include sheet-stealing and differing bedtimes and room-temperature preferences.

Sleep experts suggest there are ways to address these couple-sleep problems -- without resorting to separate bedrooms.

'Sleep is a critically important health behavior that we know is associated with heart disease and psychiatric well-being,' says Wendy M. Troxel, an assistant professor of psychiatry and psychology at the University of Pittsburgh. 'It happens to be this health behavior that we do in couples,' she says. In one of Dr. Troxel's studies, published in 2009, women in long-term stable relationships fell asleep more quickly and woke up less during the night than single women or women who lost or gained a partner during the six to eight years of the study.

While the science is in the early stages, one hypothesis suggests that by promoting feelings of safety and security, shared sleep in healthy relationships may lower levels of cortisol, a stress hormone. Sharing a bed may also reduce cytokines, involved in inflammation, and boost oxytocin, the so-called love hormone that is known to ease anxiety and is produced in the same part of the brain responsible for the sleep-wake cycle. So even though sharing a bed may make people move more, 'the psychological benefits we get having closeness at night trump the objective costs of sleeping with a partner,' Dr. Troxel says.

Peter B. Ellis needs six hours of sleep and likes to go to bed at midnight. His wife, Nanci, needs eight. Her ideal bedtime is 10 p.m. For years, Ms. Ellis, a 42-year-old television and movie writer now staying home with the couple's 2-year-old son, tried to adopt her husband's schedule. 'I became sleep deprived and really grumpy,' she says. 'We were fighting more and we were distant from each other,' says Mr. Ellis, a 49-year-old film editor.

Mr. Ellis says he couldn't understand how anyone could need more sleep than he did. 'I thought, 'She's just lazy,' ' he says. Mr. Ellis says he began to understand the legitimacy of their different sleep needs after he was diagnosed with sleep apnea in 2008, had surgery to treat it and stopped getting tired in the afternoon. Then, in 2009, the couple's son was born and they took a hard look at their sleep arrangements.

Now, some nights, the Los Angeles-based couple goes to bed at midnight. Other nights, they go to bed at 10 p.m. On nights when they have different bedtimes, Ms. Ellis may take an Ambien sleeping pill, which keeps her from waking up when Mr. Ellis comes to bed later. In the morning, Mr. Ellis usually gets up with their three children and Ms. Ellis sleeps in.

Mismatched body clocks -- a night owl with a so-called lark, for example -- can be tough on a relationship, says Jeffry H. Larson, a professor of marriage and family therapy at Brigham Young University in Provo, Utah. He led a 1991 study of 150 couples. Ones with mismatched body clocks argued more (2.13 times per week compared with 1.6 times for matched couples) and spent less time together in shared activities (about 3 hours versus about 6 hours per week). They had slightly less sex, too.

Dr. Larson counsels couples with sleep differences to 'accept that your partner is different.' Body clocks are fairly fixed: Most people can't rejigger their natural bedtime and wake time by more than one hour, he says.

Sleep specialists suggest couples with mismatched schedules initially retire together for that 'special time in bed and negotiate that [the night person] gets to leave and come back later and then gets to sleep in,' says Colleen E. Carney, associate professor at Ryerson University in Toronto.

There is a growing market for products that claim to help couples sleep better together. Tempur-Pedic International Inc. says the promise that its mattresses 'don't transfer motion' from one tossing and turning person to another is a key reason customers buy them, says Rick Anderson, president of Tempur-Pedic, North America. Its iconic advertising image is a glass of red wine perched on the edge of a bed. (On YouTube, homemade videos show customers jumping on their beds trying to topple wine and water glasses.) Tempur-Pedic's world-wide sales have grown to $1.4 billion in 2011 from $831 million in 2009. Select Comfort Corp.'s Sleep Number launched 'Create Your Perfect Comforter' in 2009. Couples can customize the amount of filling in each half of the comforter. The company has sold mattresses in which people can adjust each side's firmness since 1987.

In a study in the journal Sleep and Biological Rhythms in 2007, women woke up more during the night when they shared a bed compared with when they were alone. (Nocturnal awakenings were measured by actigraphs, wrist devices that record movement.) Men slept as well when sharing a bed as when alone.

When researchers simply asked participants about their sleep the night before, men said they slept better with their partners. Women said they slept better only on nights they had sex. But their actigraphs showed otherwise. In fact, their sleep was even more fragmented on nights they had sex.

'Women enjoy male presence psychologically even though it costs them minutes or even hours of sleep,' says John Dittami, a behavioral endocrinologist and biological rhythms specialist at the University of Vienna and the lead author of the study. The issue is that women are more sensitive to their environments, he says. The study involved 10 young dating couples who shared a bed at least 10 nights and slept apart 10 nights for the study.

Dr. Dittami and Gerhard Klosch, a sleep researcher at the Medical University of Vienna, co-authors of the book 'Sleeping Better Together,' recommend that couples sleep with separate blankets, especially if one person is a restless sleeper.

In a 2010 study of 29 couples, women who had fewer negative interactions with their partners during the day slept better that night. For men, it was reversed: Better sleep led to fewer negative interactions with their partners the next day.

Interestingly, on the days women said they had more positive interactions with their partners and fewer negative ones, the men slept better at night, too. 'Women tend to drive the emotional content of the relationships,' says Dr. Troxel, who co-wrote the study. 'Husbands may take up a stronger signal' from wives.

Clearing up a relationship issue can sometimes ease insomnia, says Christina S. McCrae, associate professor at the University of Florida and president of the Society of Behavioral Sleep Medicine. She has had several patients whose sleep improved after underlyingrelationship problems were addressed with their spouses during sleep-therapy sessions.