They also had less risk of sleep apnoea, a condition where breathing is interrupted, leading to gasping for air in the night.
Brandon Fuentes, the lead author and an undergraduate researcher at the University of Arizona's department of psychiatry, said: "Sleeping with a romantic partner or spouse shows to have great benefits on sleep health, including reduced sleep apnoea risk, sleep insomnia severity and overall improvement in sleep quality."
More couples sleep separately
The number of couples who live together but choose to sleep separately has doubled in the past decade in Britain, where one in six (15 per cent) now prefer to be alone at night, according to the National Bed Federation.
Nearly 90 per cent of those who chose to sleep separately moved into their own bedroom.
A survey for The Sleep Charity last year found Northern Ireland had the highest number of couples sleeping apart, at 21 per cent, while the South East had the fewest, at 9 per cent.
Couples who had been married the longest were the most likely to prefer separate beds: 22 per cent of over-65s slept alone compared with nobody aged 18-24.
Even sex counsellors are now recommending separate beds to improve a relationship.
Bedroom incompatibility
Relationship experts claim many couples suffer bedroom incompatibility, often having vastly different sleep schedules, or being forced to cope with a partner's sleepwalking, bathroom visits or need for a different temperature or level of darkness.
A University of California study found poor sleep can result in conflicts, so experts believe enjoying nights free of disturbances could improve relationships.
The Sleep Charity said it was "quite sensible to sleep apart if your partner causes you disturbed sleep on a regular basis".
Lonely sleepers more tired, depressed and anxious
However, the latest research found that people who slept on their own were more likely to be tired, depressed and anxious.
The only time when it was beneficial to sleep alone was when the alternative was sleeping with a child of a different family member, which was found to hinder rest.
Dr Michael Grandner, the senior study author and the director of the University of Arizona's sleep and health research programme, added: "Very few research studies explore this, but our findings suggest that whether we sleep alone or with a partner or family member may impact our sleep health.
"We were very surprised to find out just how important this could be."
The study was presented at Sleep 2022, the annual meeting of the Associated Professional Sleep Societies, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.
