A study from Sweden offers the first scientific evidence that there is indeed such a thing as beauty sleep. And that if you don't get enough of it, you'll wake up looking like something that the cat dragged in.

On average, the sleep deprived people were judged as 19% more tired, 6% less healthy and 4% less attractive.

When observers were shown photographs of well rested people and compared them to photos of the same people taken when they were sleep deprived, the sleep deprived people were consistently seen as less attractive, less healthy and more tired.

While the differences seen by the observers were fairly small, they were apparent from just a six-second glance at a still photograph. The researchers suspect that in real life situations, where there are additional cues available and more time to see them, they'd appear much larger — sleep deprived people would seem even more tired, less healthy and less attractive.

In the study, 23 people between the ages of 18 and 31 were photographed between 2 and 3 PM on two different occasions. On the well-rested occasion, they had slept at least eight hours the night before. On the sleep deprived occasion, they had slept no more than five hours and were afterwards awake for 31 hours straight. Participants slept at home and both kept sleep diaries and sent text messages to the researchers before going to sleep and after waking up. The sleep deprived subjects spent their final 16 hours of wakefulness in the sleep lab, to insure that they did not nap.

For the photo shoot, participants wore no makeup, had their hair loose (combed backwards if long), underwent similar cleaning or shaving procedures for both photos, and were instructed to sit up straight and look directly into the camera, with a neutral, relaxed facial expression.

The photos were shown to 65 untrained observers, most of whom were students at the Karolinska Institute. From a six-second glance, the observers rated the photos for attractiveness, health and tiredness on a 100-point scale.

On average, the sleep deprived people were judged as 19% more tired, 6% less healthy and 4% less attractive.

These results have obvious implications for everything from medical diagnoses to personal life. And they seem to be saying that operating on short sleep is no way to impress anyone.

An article detailing the study appears in the Christmas 2010 issue of the British Medical Journal (BMJ) and is freely available.