Sharing your bed can reduce your brain power - but only if you are a man, say scientists.

When men spend the night in the same bed with someone else their sleep patterns are disturbed, even if they do not make love, new research shows.

And this leads to poorer performance in mental agility tests the next day.

However women do not suffer the same problem. They too have disturbed sleep if they share a bed, but tend to get better quality rest when they do finally drop off . This means their brain power remains undiminished.

The finding suggests that if a man has an important day ahead he would be best to head off to the spare room to sleep rather than sharing the marital bed.

A team led by Professor Gerhard Kloesch at the University of Vienna recruited eight unmarried, childless couples in their twenties for their study.

He asked them to spend 10 nights sleeping apart and ten together while he monitored their rest patterns at night through wrist monitors and sleep diaries.

The next day he gave them mental ability or 'cognitive' tests.

Even without having sex, everyone had more disturbed sleep when sharing a bed than alone but the effects of this on the brain only affected the men, according to the finding.

According to the research report, lack of sleep led to increased stress hormone levels in men and reduced their ability to perform simple cognitive tests the next day.

However women seemed to show no such ill-effects even if their sleep was just as disturbed. The researchers found women were more refreshed than men even when they slept the same number of hours and so concluded they must sleep more deeply.

The study also found sharing a bed can impact on dreams. Typically women remembered more of their dreams after sleeping alone while men recalled the most after sex.