The best way to keep a marriage happy is to sleep in the nude, a study suggests.

London - Snoring, sweating, stealing the sheets… it’s little wonder that an estimated one in four couples insist on sleeping in separate rooms.

Now, however, there’s an emerging body of research to suggest there could be health benefits to sharing a bed with a long-term partner.

It’s even been suggested as a major reason why people in close relationships tend to be in better health and live longer.

Researchers from the University of Pittsburgh in the US believe sleeping next to someone helps lower the stress hormone cortisol, perhaps because it encourages feelings of safety and security.

Prolonged periods of elevated cortisol have been linked with an increase in cytokines – proteins involved in inflammation that can trigger heart disease, depression and autoimmune disorders. Sleeping together has a protective effect by lowering the levels of these proteins.

“Sleep is a critically important health behaviour that we know is associated with heart disease and psychiatric well-being,” says lead researcher Wendy Troxel, assistant professor of psychiatry and psychology at the university.

“There is extensive literature showing that married people – happily married people, in particular – live longer, happier, and healthier lives than their unmarried or unhappy counterparts.

“We also know sleep is critically important for health and wellbeing, and it happens to be a behaviour couples engage in together, so it stands to reason it may be an important link with their health.”

Sharing a bed is also thought to boost levels of the “love hormone” oxytocin, known to induce bonding feelings.

This is traditionally thought to be released during sex, but Dr David Hamilton, a scientist who has examined the role of oxytocin in health in his book, Why Kindness is Good For You, says it’s also associated with cuddling in bed and “pillow talk”.

“Sleeping together will increase oxytocin levels, provided you are happy in the relationship,” he says.

“Making love is one of the most reliable ways to produce oxytocin, as is going to sleep embracing someone or just being physically happy in their company or with the conversation you are having in bed.

“And oxytocin has a super-spiral effect; the more physical contact you have, the more oxytocin you’ll produce, which causes you to want more contact, and so on… Oxytocin can have an addictive effect.”

Recent studies have shown oxytocin’s vital role in health.

Scientists at Malmo University Hospital in Sweden found it can affect digestion.

Those with lower levels had poorer gastric motility – the process by which food is moved from the stomach to the intestines, therefore slowing down digestion. Levels of the hormone have been found to be lower in patients with irritable bowel syndrome, says Hamilton.

“Oxytocin has also been shown to reduce inflammation. While inflammation is a necessary part of the healing process, too much of it, which can accompany bacterial infections or chronic stress, is damaging to the body.

“It’s well known, for example, that inflammation plays a role in many types of cancer.

“Meanwhile, a number of recent studies have shown how oxytocin can affect the heart.”

For example, a study from the University of North Carolina asked 59 women who were married or had partners to keep a diary of the number of hugs they received over a set time.

The scientists then analysed levels of oxytocin in the blood. The women who’d received the most hugs had the highest levels of oxytocin – and the lowest blood pressure and heart rates.

“Indeed, oxytocin is like a natural angina medication,” says Hamilton. “Angina medication is basically nitric oxide, which expand blood vessels. Oxytocin helps the body produce nitric oxide itself.”

It may come as a surprise to the long-suffering partners of snorers, teeth-grinders and kickers, but sharing a bed may also improve your sleep. In another of Troxel’s studies, published in 2009, women in long-term stable relationships fell asleep more quickly and woke up less frequently during the night than single women or women who lost or gained a partner during the six to eight years of the study.

“Feelings of safety and security with a partner may lead to more restful sleep,” she says.

These findings are interesting given that men move around more in bed than women, according to Professor Jim Horne, director of the sleep research centre at Loughborough University.

“In fact, research we did showed the biggest cause of sleep disturbance is a bed partner,” he says.

“Despite this, if the man was absent from the bed, the woman moved around more than normal, so her sleep was still disturbed. Though her male partner was a nuisance when he was there, her sleep was still affected when he wasn’t.”

Women do reap more benefits from bed sharing than men, says Dr Jason Ellis, a chartered psychologist and director of Northumbria Centre for Sleep Research.

“These benefits tend to be psychological rather than physiological, but nevertheless, the women we studied reported more enjoyable and refreshing sleep when sharing a bed compared to the men,” he says.

“As sleeping alone has been shown to elevate levels of the stress hormone cortisol, it might be an evolutionary thing related to feeling less secure or supported – though the long-term health implications of that have yet to be studied.”

Troxel adds bed partners can also play a crucial role in diagnosing the other’s health problems and sleep disorders such as obstructive sleep apnoea – where the muscles and soft tissues in the throat relax and collapse sufficiently to block the airway. One of the main symptoms is heavy snoring. Left untreated, it increases the risk of diabetes, heart disease and stroke.

A number of couples believe sharing a bed has saved their lives, says Paul Rosenblatt, professor of family social science at the University of Minnesota and author of Two in a Bed: The social system of couple bed sharing.

“I spoke with a man who slept every night cuddling his wife and so immediately noticed when she had a seizure,” he says.

“Similar stories came from couples where one partner had gone into diabetic shock.”

He found that many of the couples interviewed said they would get a better night’s sleep apart. “But they didn’t want to sleep separately because of the intimacy of sharing a bed, the security and the sense of belonging together.”

It’s clear the benefits of sharing a bed only appear if the relationship is happy – and you can tolerate sharing a bed with your partner.

“What we do know about couples and sleep is that happily married women have fewer sleep problems than their unhappily married counterparts,” says Troxel. “Couples who are mismatched in terms of their preferences for sleep timing, have poorer relationship functioning (that is, more conflict, less intimacy, less support) will not reap so many benefits.” – Daily Mail

Four tips on how to banish pillow fights

* “Men tend to prefer harder mattresses because they don’t have the contours – the lumps and bumps – women have,” says Sammy Margo, a chartered physiotherapist and author of The Good Sleep Guide. The problem can be solved by buying a mattress in two parts – one half firm, one soft. The bigger each mattress, the less noticeable the other’s movements will be.

* If sharing a bed with your partner seems an unbearable thought, there is a solution. “Sleep apart in the week, when good-quality sleep is important, and together on weekends, getting the best of both worlds,” says sleep therapist Dr Nerina Ramlakhan.

* “Room temperature is a common problem for bed sharers,” says Ramlakhan. The best sleep happens when your brain is cooler than your body. One solution is use separate single duvets.

* If your partner is a snorer, encourage them to seek treatment. “And go to bed first,” says Margo. “If you are in deeper stages of sleep when your partner joins you, his or her snoring is less likely to interrupt your sleep.” – Daily Mail