They are supposed to warm the heart. But we don't just watch romantic comedies when we're feeling blue - we also pick them when we're cold, claim researchers.

In an experiment, they found viewers subconsciously chose to watch love stories when they felt chilly. And they analysed industry figures which showed that rentals of "rom-com" DVDs go up when the mercury drops.

Scientists at Hong Kong's University of Science and the University of Colorado in the US divided volunteers into two groups. They gave one set hot drinks to increase their body temperature, and cold ones to the other group to reduce it. In all cases, those who were colder chose a romantic film.

"Romance movies are more desirable when people are physically cold, because coldness activates a need for psychological warmth," they wrote in the Journal of Consumer Research.