Having sex is the best way to stop daydreaming!

Mind-wandering turns out to be extremely common - users reported daydreaming almost 50 per cent of the time - mostly during brushing their teeth or doing other grooming, reports New Scientist.

During only one activity - making love - did the frequency of mind-wandering drop below 30 per cent.

Crucially, episodes of mind-wandering tended to precede bouts of low mood, but not vice versa, suggesting that the former caused the latter.

Matthew Killingsworth and colleague Daniel Gilbert of Harvard University conducted the study, and found that daydreams about pleasant things were linked to improvements in mood, but only slight improvements.

Thinking about neutral topics while mind-wandering was linked to a similarly modest drop in happiness, but daydreams about unpleasant topics coincided with a sharp drop.

But the claim that mind-wandering causes unhappiness needs to be further evaluated, they said, because he and others have shown the effect can run in the opposite direction.

"It''s difficult to make causal claims. But it''s undoubtedly the case that negative mood and mind-wandering are inextricably linked," Jonathan Smallwood at the University of California, Santa Barbara.

The connection suggests that cutting down on mind-wandering, either by practising meditation or simply by keeping busy, could help people battle depression.

"The irony is that mind-wandering also underlies invention. We don''t want to tell people not to do it," Smallwood said.

The study is published in Science.u00a0