In the study, published Tuesday on BMJ.com, John Axelsson of the Karolinska Institute looked at the effect that sleep, or its lack, had on the way other people perceived the attractiveness of the sleeper.

Axelsson's interest in the subject was partly inspired by a question from his young daughter about whether it was the long nap that made Sleeping Beauty so lovely. And, partly, it was that he saw a gap in the scholarship. "The field of sleep research is full of studies showing the physiological and cognitive consequences of disturbed sleep," he says, "while there is clear lack of how poor sleep affects our everyday social life."

It's estimated that about 40 million people suffer from chronic sleep disorders in the U.S. and a further 20 million have frequent problems sleeping. Even for good sleepers, with holiday and New Year's celebrations oncoming, this is among the most slumber-deprived of seasons.

For the study, 23 participants, all between the prime partying ages of 18 to 31, were recruited. They were asked to sit for photographs in the afternoon, between 2 p.m. and 3 p.m. This time "coincides with the afternoon dip, or siesta time, a time where most people are sleepier," says Axelsson. And unlike office workers, the study volunteers were not allowed to consume a mid-afternoon caffeinated beverage to keep them going.

Each photograph was identical — lit the same way, the same distance from the camera, with no makeup and natural hairstyles. The subjects were told to have a relaxed, neutral expression. They weren't allowed to drink alcohol for the 48 hours prior to the experiment. The only difference among the volunteers was that some had had a full night's sleep the night before, while others had been awake for 31 hours straight, after just five hours of sleep the previous night.

The photos were then shown to a group of 65 different people, who, knowing nothing about how tired the people in the photos were, rated their attractiveness. The observers rated the sleep-deprived as less healthy looking, less fetching and, obviously, more tired-looking.

Of course, anyone who's ever pulled an all-nighter knows that it's no formula for good looks — the next day, you're saddled with puffy, bloodshot eyes, dark circles and a wan complexion — but now there's a study to prove it. So if the old adage about getting your beauty sleep is true, what does that mean for watched pots never boiling, or crying over spilled milk? Probably nothing, but Axelsson is curious. "There are so many old 'sayings' or beliefs incorporated in our culture, but we do not know if they are true," he says. "It is our scientists' responsibility to evaluate the truth in them."