The Sleep Council reports that when couples share a bed both may be woken about six times during the night by their partners, The Times of London said. The problem is worse if one or both snores or has restless leg syndrome.

About 25 percent of British adults snore, the British Snoring and Sleep Apnea Association said. The problem may cost their partners two hours of sleep every night.

In the United States, researchers at the University of Wisconsin found that the greatest marital problems seem to occur when one partner is a lark, getting up early in the morning ready for the day, and the other an owl who prefers to stay up late and sleep in. A California woman ended up getting a divorce because she got fed up with her husband's habit of staying up late playing computer games.

For other couples, separate bedrooms could be the right choice. The National Association of Home Builders predicted that by 2015 a majority of custom-built homes will have his-and-hers master bedrooms.